Used to measure rates of processes in the oceanRates of removal of reactive chemical species

bull Air-sea exchangebull Particle scavenging

Rate of sediment accumulation Growth rates of authigenic deposits and marine organisms (eg Mn nodules coral skeletons shells) Rates of sediment mixing by benthic organismsMixing rates in water amp water mass tracing Aging of organic matter

Radionuclides (geochronometers and tracers)

Primordial - Present since Earthrsquos formation (long lived nuclides)

Cosmogenic - Formed by cosmic rays in the atmosphere

Anthropogenic - Man made (nuclear reactors bombs etc)

Types of natural radionuclides in the environment

Less than 21 kg of 3H on the entire Earth ndash and this can be measured in a few liters of water

- results in change in the neutronproton ratio

- decay results from thermodynamic instability of the nucleus and is an attempt to reach the most stable nuclear configuration

Nuclear decay

Different modes of nuclear decay

Alpha decay () of larger nuclides - loss of a helium nucleus (4

2He) to lower neutronproton ratio Mass and element changes

23892U --gt 234

90Th + 42He + Q (radiation eg gamma rays)

Beta decay (-) - converts a neutron to a proton with emission of a high energy electron (e-) - for atoms with extra neutrons

146C --gt 14

7N + e- note increase in protons changes element but not mass

Electron capture - proton in nucleus grabs an electron from lowest orbital and combines to form a neutron To fill empty orbital another e- falls to lower energy level emitting X-rays

4019K --gt 40

18Ar note decrease in protons changes element but not mass

Ion or mineral

Inert gas

238U

Irsquom bored I donrsquot want to be

uranium any more

t12 = 45 billion years

Parent nuclide

234234ThThAlpha decay 42He +

t12 = 241 days

Daughter nuclide

Life is short - and then you decay

All primordial series end with stable (non-radioactive) form of lead (Pb)

α decay

β decay

Characteristics of Uranium and Thorium Series - Primordial Nuclides

Element Name T12 range Chemistry in Oceans

U Uranium 25x105 - 45 x 109 y Soluble in seawater

especially in oxic waters Insoluble in reduced form Conservative with salinity

Pa Protactinium 12 min - 32 x 104 y Particle reactive - surface adsorbed

Th Thorium 26h-14 x 1010 y Particle reactive - surface adsorbed Chemistry similar to iron

Ac Actinum 6h - 22 y Particle reactive Short lived

Ra Radium 36 d - 1600 y Soluble chemistry like Ca

Rn Radon 4 sec - 38 days Noble gas - unreactive soluble

Po Polonium 10-7 sec - 138 days Nutrient element behavior

Pb Lead 30 min - 22 y Reactive heavy metal tracer-particle reactive

Detection of radioactivity

ionization detector- energy windows (each nuclide decay emits a characteristic energy spectrum (eg photons of gamma radiation) and can be distinguished from another)

Fission tracks

Scintillation counting (uses chemicals to absorb radiation energy leading to chain reactions that produce light Light pulses are detected with high sensitivity Again different nuclides can be distinguished based on energy of emission

Radiation is the amount of energy emitted

Radioactivity is a measure of nuclear disintegrations per unit time often given as disintegrations per minute (dpm)

Each time a nucleus decays it is an ldquoeventrdquo or disintegration

Common units of radioactivityCurie = 222 x 1012 disintegrations per minute (dpm) A curie is defined by the amount of radioactivity in 1 gram of Radium

In practice we commonly work in millicuries (222 x 109 dpm) or microcuries (222 x 106 dpm) or just plain dpm

Becquerel - The SI unit for radioactivity

1Bq = 1 disintegrationsec (dps)

So one Curie is = 37 x 1010 Becquerels (dps)

Specific activity ndash the amount of radioactivity per mole of substance eg mCimmol or dpmpmol

238U is the most abundant radionuclide in seawater

~3 g liter-1 mainly as uranyl tricarbonate [UO2(CO3)3]-4 which has uranium in the oxidized form U(+VI) [Uranium] is conservative with salinity

238U dpmliter = 007081 x salinity

In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Uranium (+VI) can be reduced by microbes under anoxic conditions adding 2 e- and producing U(+IV) This form is insoluble and precipitates Iron reducing bacteria can carry out this reduction (much interest in this)

At salinity = 35 238U activity = 248 dpmLiter of seawater

For nuclides in solution the chemical concentration (Nliter) is directly proportional to radioactivity per liter (Nliter) since

The absolute concentrations of many nuclides in seawater is very low and not easily measured by chemical means But their radioactivity can be measured

Emerson amp Hedges 2008 Chap 5Emerson amp Hedges 2008 Chap 5

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Primordial - Present since Earthrsquos formation (long lived nuclides)

Cosmogenic - Formed by cosmic rays in the atmosphere

Anthropogenic - Man made (nuclear reactors bombs etc)

Types of natural radionuclides in the environment

Less than 21 kg of 3H on the entire Earth ndash and this can be measured in a few liters of water

- results in change in the neutronproton ratio

- decay results from thermodynamic instability of the nucleus and is an attempt to reach the most stable nuclear configuration

Nuclear decay

Different modes of nuclear decay

Alpha decay () of larger nuclides - loss of a helium nucleus (4

2He) to lower neutronproton ratio Mass and element changes

23892U --gt 234

90Th + 42He + Q (radiation eg gamma rays)

Beta decay (-) - converts a neutron to a proton with emission of a high energy electron (e-) - for atoms with extra neutrons

146C --gt 14

7N + e- note increase in protons changes element but not mass

Electron capture - proton in nucleus grabs an electron from lowest orbital and combines to form a neutron To fill empty orbital another e- falls to lower energy level emitting X-rays

4019K --gt 40

18Ar note decrease in protons changes element but not mass

Ion or mineral

Inert gas

238U

Irsquom bored I donrsquot want to be

uranium any more

t12 = 45 billion years

Parent nuclide

234234ThThAlpha decay 42He +

t12 = 241 days

Daughter nuclide

Life is short - and then you decay

All primordial series end with stable (non-radioactive) form of lead (Pb)

α decay

β decay

Characteristics of Uranium and Thorium Series - Primordial Nuclides

Element Name T12 range Chemistry in Oceans

U Uranium 25x105 - 45 x 109 y Soluble in seawater

especially in oxic waters Insoluble in reduced form Conservative with salinity

Pa Protactinium 12 min - 32 x 104 y Particle reactive - surface adsorbed

Th Thorium 26h-14 x 1010 y Particle reactive - surface adsorbed Chemistry similar to iron

Ac Actinum 6h - 22 y Particle reactive Short lived

Ra Radium 36 d - 1600 y Soluble chemistry like Ca

Rn Radon 4 sec - 38 days Noble gas - unreactive soluble

Po Polonium 10-7 sec - 138 days Nutrient element behavior

Pb Lead 30 min - 22 y Reactive heavy metal tracer-particle reactive

Detection of radioactivity

ionization detector- energy windows (each nuclide decay emits a characteristic energy spectrum (eg photons of gamma radiation) and can be distinguished from another)

Fission tracks

Scintillation counting (uses chemicals to absorb radiation energy leading to chain reactions that produce light Light pulses are detected with high sensitivity Again different nuclides can be distinguished based on energy of emission

Radiation is the amount of energy emitted

Radioactivity is a measure of nuclear disintegrations per unit time often given as disintegrations per minute (dpm)

Each time a nucleus decays it is an ldquoeventrdquo or disintegration

Common units of radioactivityCurie = 222 x 1012 disintegrations per minute (dpm) A curie is defined by the amount of radioactivity in 1 gram of Radium

In practice we commonly work in millicuries (222 x 109 dpm) or microcuries (222 x 106 dpm) or just plain dpm

Becquerel - The SI unit for radioactivity

1Bq = 1 disintegrationsec (dps)

So one Curie is = 37 x 1010 Becquerels (dps)

Specific activity ndash the amount of radioactivity per mole of substance eg mCimmol or dpmpmol

238U is the most abundant radionuclide in seawater

~3 g liter-1 mainly as uranyl tricarbonate [UO2(CO3)3]-4 which has uranium in the oxidized form U(+VI) [Uranium] is conservative with salinity

238U dpmliter = 007081 x salinity

In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Uranium (+VI) can be reduced by microbes under anoxic conditions adding 2 e- and producing U(+IV) This form is insoluble and precipitates Iron reducing bacteria can carry out this reduction (much interest in this)

At salinity = 35 238U activity = 248 dpmLiter of seawater

For nuclides in solution the chemical concentration (Nliter) is directly proportional to radioactivity per liter (Nliter) since

The absolute concentrations of many nuclides in seawater is very low and not easily measured by chemical means But their radioactivity can be measured

Emerson amp Hedges 2008 Chap 5Emerson amp Hedges 2008 Chap 5

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Less than 21 kg of 3H on the entire Earth ndash and this can be measured in a few liters of water

- results in change in the neutronproton ratio

- decay results from thermodynamic instability of the nucleus and is an attempt to reach the most stable nuclear configuration

Nuclear decay

Different modes of nuclear decay

Alpha decay () of larger nuclides - loss of a helium nucleus (4

2He) to lower neutronproton ratio Mass and element changes

23892U --gt 234

90Th + 42He + Q (radiation eg gamma rays)

Beta decay (-) - converts a neutron to a proton with emission of a high energy electron (e-) - for atoms with extra neutrons

146C --gt 14

7N + e- note increase in protons changes element but not mass

Electron capture - proton in nucleus grabs an electron from lowest orbital and combines to form a neutron To fill empty orbital another e- falls to lower energy level emitting X-rays

4019K --gt 40

18Ar note decrease in protons changes element but not mass

Ion or mineral

Inert gas

238U

Irsquom bored I donrsquot want to be

uranium any more

t12 = 45 billion years

Parent nuclide

234234ThThAlpha decay 42He +

t12 = 241 days

Daughter nuclide

Life is short - and then you decay

All primordial series end with stable (non-radioactive) form of lead (Pb)

α decay

β decay

Characteristics of Uranium and Thorium Series - Primordial Nuclides

Element Name T12 range Chemistry in Oceans

U Uranium 25x105 - 45 x 109 y Soluble in seawater

especially in oxic waters Insoluble in reduced form Conservative with salinity

Pa Protactinium 12 min - 32 x 104 y Particle reactive - surface adsorbed

Th Thorium 26h-14 x 1010 y Particle reactive - surface adsorbed Chemistry similar to iron

Ac Actinum 6h - 22 y Particle reactive Short lived

Ra Radium 36 d - 1600 y Soluble chemistry like Ca

Rn Radon 4 sec - 38 days Noble gas - unreactive soluble

Po Polonium 10-7 sec - 138 days Nutrient element behavior

Pb Lead 30 min - 22 y Reactive heavy metal tracer-particle reactive

Detection of radioactivity

ionization detector- energy windows (each nuclide decay emits a characteristic energy spectrum (eg photons of gamma radiation) and can be distinguished from another)

Fission tracks

Scintillation counting (uses chemicals to absorb radiation energy leading to chain reactions that produce light Light pulses are detected with high sensitivity Again different nuclides can be distinguished based on energy of emission

Radiation is the amount of energy emitted

Radioactivity is a measure of nuclear disintegrations per unit time often given as disintegrations per minute (dpm)

Each time a nucleus decays it is an ldquoeventrdquo or disintegration

Common units of radioactivityCurie = 222 x 1012 disintegrations per minute (dpm) A curie is defined by the amount of radioactivity in 1 gram of Radium

In practice we commonly work in millicuries (222 x 109 dpm) or microcuries (222 x 106 dpm) or just plain dpm

Becquerel - The SI unit for radioactivity

1Bq = 1 disintegrationsec (dps)

So one Curie is = 37 x 1010 Becquerels (dps)

Specific activity ndash the amount of radioactivity per mole of substance eg mCimmol or dpmpmol

238U is the most abundant radionuclide in seawater

~3 g liter-1 mainly as uranyl tricarbonate [UO2(CO3)3]-4 which has uranium in the oxidized form U(+VI) [Uranium] is conservative with salinity

238U dpmliter = 007081 x salinity

In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Uranium (+VI) can be reduced by microbes under anoxic conditions adding 2 e- and producing U(+IV) This form is insoluble and precipitates Iron reducing bacteria can carry out this reduction (much interest in this)

At salinity = 35 238U activity = 248 dpmLiter of seawater

For nuclides in solution the chemical concentration (Nliter) is directly proportional to radioactivity per liter (Nliter) since

The absolute concentrations of many nuclides in seawater is very low and not easily measured by chemical means But their radioactivity can be measured

Emerson amp Hedges 2008 Chap 5Emerson amp Hedges 2008 Chap 5

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

- results in change in the neutronproton ratio

- decay results from thermodynamic instability of the nucleus and is an attempt to reach the most stable nuclear configuration

Nuclear decay

Different modes of nuclear decay

Alpha decay () of larger nuclides - loss of a helium nucleus (4

2He) to lower neutronproton ratio Mass and element changes

23892U --gt 234

90Th + 42He + Q (radiation eg gamma rays)

Beta decay (-) - converts a neutron to a proton with emission of a high energy electron (e-) - for atoms with extra neutrons

146C --gt 14

7N + e- note increase in protons changes element but not mass

Electron capture - proton in nucleus grabs an electron from lowest orbital and combines to form a neutron To fill empty orbital another e- falls to lower energy level emitting X-rays

4019K --gt 40

18Ar note decrease in protons changes element but not mass

Ion or mineral

Inert gas

238U

Irsquom bored I donrsquot want to be

uranium any more

t12 = 45 billion years

Parent nuclide

234234ThThAlpha decay 42He +

t12 = 241 days

Daughter nuclide

Life is short - and then you decay

All primordial series end with stable (non-radioactive) form of lead (Pb)

α decay

β decay

Characteristics of Uranium and Thorium Series - Primordial Nuclides

Element Name T12 range Chemistry in Oceans

U Uranium 25x105 - 45 x 109 y Soluble in seawater

especially in oxic waters Insoluble in reduced form Conservative with salinity

Pa Protactinium 12 min - 32 x 104 y Particle reactive - surface adsorbed

Th Thorium 26h-14 x 1010 y Particle reactive - surface adsorbed Chemistry similar to iron

Ac Actinum 6h - 22 y Particle reactive Short lived

Ra Radium 36 d - 1600 y Soluble chemistry like Ca

Rn Radon 4 sec - 38 days Noble gas - unreactive soluble

Po Polonium 10-7 sec - 138 days Nutrient element behavior

Pb Lead 30 min - 22 y Reactive heavy metal tracer-particle reactive

Detection of radioactivity

ionization detector- energy windows (each nuclide decay emits a characteristic energy spectrum (eg photons of gamma radiation) and can be distinguished from another)

Fission tracks

Scintillation counting (uses chemicals to absorb radiation energy leading to chain reactions that produce light Light pulses are detected with high sensitivity Again different nuclides can be distinguished based on energy of emission

Radiation is the amount of energy emitted

Radioactivity is a measure of nuclear disintegrations per unit time often given as disintegrations per minute (dpm)

Each time a nucleus decays it is an ldquoeventrdquo or disintegration

Common units of radioactivityCurie = 222 x 1012 disintegrations per minute (dpm) A curie is defined by the amount of radioactivity in 1 gram of Radium

In practice we commonly work in millicuries (222 x 109 dpm) or microcuries (222 x 106 dpm) or just plain dpm

Becquerel - The SI unit for radioactivity

1Bq = 1 disintegrationsec (dps)

So one Curie is = 37 x 1010 Becquerels (dps)

Specific activity ndash the amount of radioactivity per mole of substance eg mCimmol or dpmpmol

238U is the most abundant radionuclide in seawater

~3 g liter-1 mainly as uranyl tricarbonate [UO2(CO3)3]-4 which has uranium in the oxidized form U(+VI) [Uranium] is conservative with salinity

238U dpmliter = 007081 x salinity

In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Uranium (+VI) can be reduced by microbes under anoxic conditions adding 2 e- and producing U(+IV) This form is insoluble and precipitates Iron reducing bacteria can carry out this reduction (much interest in this)

At salinity = 35 238U activity = 248 dpmLiter of seawater

For nuclides in solution the chemical concentration (Nliter) is directly proportional to radioactivity per liter (Nliter) since

The absolute concentrations of many nuclides in seawater is very low and not easily measured by chemical means But their radioactivity can be measured

Emerson amp Hedges 2008 Chap 5Emerson amp Hedges 2008 Chap 5

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Different modes of nuclear decay

Alpha decay () of larger nuclides - loss of a helium nucleus (4

2He) to lower neutronproton ratio Mass and element changes

23892U --gt 234

90Th + 42He + Q (radiation eg gamma rays)

Beta decay (-) - converts a neutron to a proton with emission of a high energy electron (e-) - for atoms with extra neutrons

146C --gt 14

7N + e- note increase in protons changes element but not mass

Electron capture - proton in nucleus grabs an electron from lowest orbital and combines to form a neutron To fill empty orbital another e- falls to lower energy level emitting X-rays

4019K --gt 40

18Ar note decrease in protons changes element but not mass

Ion or mineral

Inert gas

238U

Irsquom bored I donrsquot want to be

uranium any more

t12 = 45 billion years

Parent nuclide

234234ThThAlpha decay 42He +

t12 = 241 days

Daughter nuclide

Life is short - and then you decay

All primordial series end with stable (non-radioactive) form of lead (Pb)

α decay

β decay

Characteristics of Uranium and Thorium Series - Primordial Nuclides

Element Name T12 range Chemistry in Oceans

U Uranium 25x105 - 45 x 109 y Soluble in seawater

especially in oxic waters Insoluble in reduced form Conservative with salinity

Pa Protactinium 12 min - 32 x 104 y Particle reactive - surface adsorbed

Th Thorium 26h-14 x 1010 y Particle reactive - surface adsorbed Chemistry similar to iron

Ac Actinum 6h - 22 y Particle reactive Short lived

Ra Radium 36 d - 1600 y Soluble chemistry like Ca

Rn Radon 4 sec - 38 days Noble gas - unreactive soluble

Po Polonium 10-7 sec - 138 days Nutrient element behavior

Pb Lead 30 min - 22 y Reactive heavy metal tracer-particle reactive

Detection of radioactivity

ionization detector- energy windows (each nuclide decay emits a characteristic energy spectrum (eg photons of gamma radiation) and can be distinguished from another)

Fission tracks

Scintillation counting (uses chemicals to absorb radiation energy leading to chain reactions that produce light Light pulses are detected with high sensitivity Again different nuclides can be distinguished based on energy of emission

Radiation is the amount of energy emitted

Radioactivity is a measure of nuclear disintegrations per unit time often given as disintegrations per minute (dpm)

Each time a nucleus decays it is an ldquoeventrdquo or disintegration

Common units of radioactivityCurie = 222 x 1012 disintegrations per minute (dpm) A curie is defined by the amount of radioactivity in 1 gram of Radium

In practice we commonly work in millicuries (222 x 109 dpm) or microcuries (222 x 106 dpm) or just plain dpm

Becquerel - The SI unit for radioactivity

1Bq = 1 disintegrationsec (dps)

So one Curie is = 37 x 1010 Becquerels (dps)

Specific activity ndash the amount of radioactivity per mole of substance eg mCimmol or dpmpmol

238U is the most abundant radionuclide in seawater

~3 g liter-1 mainly as uranyl tricarbonate [UO2(CO3)3]-4 which has uranium in the oxidized form U(+VI) [Uranium] is conservative with salinity

238U dpmliter = 007081 x salinity

In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Uranium (+VI) can be reduced by microbes under anoxic conditions adding 2 e- and producing U(+IV) This form is insoluble and precipitates Iron reducing bacteria can carry out this reduction (much interest in this)

At salinity = 35 238U activity = 248 dpmLiter of seawater

For nuclides in solution the chemical concentration (Nliter) is directly proportional to radioactivity per liter (Nliter) since

The absolute concentrations of many nuclides in seawater is very low and not easily measured by chemical means But their radioactivity can be measured

Emerson amp Hedges 2008 Chap 5Emerson amp Hedges 2008 Chap 5

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

238U

Irsquom bored I donrsquot want to be

uranium any more

t12 = 45 billion years

Parent nuclide

234234ThThAlpha decay 42He +

t12 = 241 days

Daughter nuclide

Life is short - and then you decay

All primordial series end with stable (non-radioactive) form of lead (Pb)

α decay

β decay

Characteristics of Uranium and Thorium Series - Primordial Nuclides

Element Name T12 range Chemistry in Oceans

U Uranium 25x105 - 45 x 109 y Soluble in seawater

especially in oxic waters Insoluble in reduced form Conservative with salinity

Pa Protactinium 12 min - 32 x 104 y Particle reactive - surface adsorbed

Th Thorium 26h-14 x 1010 y Particle reactive - surface adsorbed Chemistry similar to iron

Ac Actinum 6h - 22 y Particle reactive Short lived

Ra Radium 36 d - 1600 y Soluble chemistry like Ca

Rn Radon 4 sec - 38 days Noble gas - unreactive soluble

Po Polonium 10-7 sec - 138 days Nutrient element behavior

Pb Lead 30 min - 22 y Reactive heavy metal tracer-particle reactive

Detection of radioactivity

ionization detector- energy windows (each nuclide decay emits a characteristic energy spectrum (eg photons of gamma radiation) and can be distinguished from another)

Fission tracks

Scintillation counting (uses chemicals to absorb radiation energy leading to chain reactions that produce light Light pulses are detected with high sensitivity Again different nuclides can be distinguished based on energy of emission

Radiation is the amount of energy emitted

Radioactivity is a measure of nuclear disintegrations per unit time often given as disintegrations per minute (dpm)

Each time a nucleus decays it is an ldquoeventrdquo or disintegration

Common units of radioactivityCurie = 222 x 1012 disintegrations per minute (dpm) A curie is defined by the amount of radioactivity in 1 gram of Radium

In practice we commonly work in millicuries (222 x 109 dpm) or microcuries (222 x 106 dpm) or just plain dpm

Becquerel - The SI unit for radioactivity

1Bq = 1 disintegrationsec (dps)

So one Curie is = 37 x 1010 Becquerels (dps)

Specific activity ndash the amount of radioactivity per mole of substance eg mCimmol or dpmpmol

238U is the most abundant radionuclide in seawater

~3 g liter-1 mainly as uranyl tricarbonate [UO2(CO3)3]-4 which has uranium in the oxidized form U(+VI) [Uranium] is conservative with salinity

238U dpmliter = 007081 x salinity

In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Uranium (+VI) can be reduced by microbes under anoxic conditions adding 2 e- and producing U(+IV) This form is insoluble and precipitates Iron reducing bacteria can carry out this reduction (much interest in this)

At salinity = 35 238U activity = 248 dpmLiter of seawater

For nuclides in solution the chemical concentration (Nliter) is directly proportional to radioactivity per liter (Nliter) since

The absolute concentrations of many nuclides in seawater is very low and not easily measured by chemical means But their radioactivity can be measured

Emerson amp Hedges 2008 Chap 5Emerson amp Hedges 2008 Chap 5

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

All primordial series end with stable (non-radioactive) form of lead (Pb)

α decay

β decay

Characteristics of Uranium and Thorium Series - Primordial Nuclides

Element Name T12 range Chemistry in Oceans

U Uranium 25x105 - 45 x 109 y Soluble in seawater

especially in oxic waters Insoluble in reduced form Conservative with salinity

Pa Protactinium 12 min - 32 x 104 y Particle reactive - surface adsorbed

Th Thorium 26h-14 x 1010 y Particle reactive - surface adsorbed Chemistry similar to iron

Ac Actinum 6h - 22 y Particle reactive Short lived

Ra Radium 36 d - 1600 y Soluble chemistry like Ca

Rn Radon 4 sec - 38 days Noble gas - unreactive soluble

Po Polonium 10-7 sec - 138 days Nutrient element behavior

Pb Lead 30 min - 22 y Reactive heavy metal tracer-particle reactive

Detection of radioactivity

ionization detector- energy windows (each nuclide decay emits a characteristic energy spectrum (eg photons of gamma radiation) and can be distinguished from another)

Fission tracks

Scintillation counting (uses chemicals to absorb radiation energy leading to chain reactions that produce light Light pulses are detected with high sensitivity Again different nuclides can be distinguished based on energy of emission

Radiation is the amount of energy emitted

Radioactivity is a measure of nuclear disintegrations per unit time often given as disintegrations per minute (dpm)

Each time a nucleus decays it is an ldquoeventrdquo or disintegration

Common units of radioactivityCurie = 222 x 1012 disintegrations per minute (dpm) A curie is defined by the amount of radioactivity in 1 gram of Radium

In practice we commonly work in millicuries (222 x 109 dpm) or microcuries (222 x 106 dpm) or just plain dpm

Becquerel - The SI unit for radioactivity

1Bq = 1 disintegrationsec (dps)

So one Curie is = 37 x 1010 Becquerels (dps)

Specific activity ndash the amount of radioactivity per mole of substance eg mCimmol or dpmpmol

238U is the most abundant radionuclide in seawater

~3 g liter-1 mainly as uranyl tricarbonate [UO2(CO3)3]-4 which has uranium in the oxidized form U(+VI) [Uranium] is conservative with salinity

238U dpmliter = 007081 x salinity

In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Uranium (+VI) can be reduced by microbes under anoxic conditions adding 2 e- and producing U(+IV) This form is insoluble and precipitates Iron reducing bacteria can carry out this reduction (much interest in this)

At salinity = 35 238U activity = 248 dpmLiter of seawater

For nuclides in solution the chemical concentration (Nliter) is directly proportional to radioactivity per liter (Nliter) since

The absolute concentrations of many nuclides in seawater is very low and not easily measured by chemical means But their radioactivity can be measured

Emerson amp Hedges 2008 Chap 5Emerson amp Hedges 2008 Chap 5

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Characteristics of Uranium and Thorium Series - Primordial Nuclides

Element Name T12 range Chemistry in Oceans

U Uranium 25x105 - 45 x 109 y Soluble in seawater

especially in oxic waters Insoluble in reduced form Conservative with salinity

Pa Protactinium 12 min - 32 x 104 y Particle reactive - surface adsorbed

Th Thorium 26h-14 x 1010 y Particle reactive - surface adsorbed Chemistry similar to iron

Ac Actinum 6h - 22 y Particle reactive Short lived

Ra Radium 36 d - 1600 y Soluble chemistry like Ca

Rn Radon 4 sec - 38 days Noble gas - unreactive soluble

Po Polonium 10-7 sec - 138 days Nutrient element behavior

Pb Lead 30 min - 22 y Reactive heavy metal tracer-particle reactive

Detection of radioactivity

ionization detector- energy windows (each nuclide decay emits a characteristic energy spectrum (eg photons of gamma radiation) and can be distinguished from another)

Fission tracks

Scintillation counting (uses chemicals to absorb radiation energy leading to chain reactions that produce light Light pulses are detected with high sensitivity Again different nuclides can be distinguished based on energy of emission

Radiation is the amount of energy emitted

Radioactivity is a measure of nuclear disintegrations per unit time often given as disintegrations per minute (dpm)

Each time a nucleus decays it is an ldquoeventrdquo or disintegration

Common units of radioactivityCurie = 222 x 1012 disintegrations per minute (dpm) A curie is defined by the amount of radioactivity in 1 gram of Radium

In practice we commonly work in millicuries (222 x 109 dpm) or microcuries (222 x 106 dpm) or just plain dpm

Becquerel - The SI unit for radioactivity

1Bq = 1 disintegrationsec (dps)

So one Curie is = 37 x 1010 Becquerels (dps)

Specific activity ndash the amount of radioactivity per mole of substance eg mCimmol or dpmpmol

238U is the most abundant radionuclide in seawater

~3 g liter-1 mainly as uranyl tricarbonate [UO2(CO3)3]-4 which has uranium in the oxidized form U(+VI) [Uranium] is conservative with salinity

238U dpmliter = 007081 x salinity

In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Uranium (+VI) can be reduced by microbes under anoxic conditions adding 2 e- and producing U(+IV) This form is insoluble and precipitates Iron reducing bacteria can carry out this reduction (much interest in this)

At salinity = 35 238U activity = 248 dpmLiter of seawater

For nuclides in solution the chemical concentration (Nliter) is directly proportional to radioactivity per liter (Nliter) since

The absolute concentrations of many nuclides in seawater is very low and not easily measured by chemical means But their radioactivity can be measured

Emerson amp Hedges 2008 Chap 5Emerson amp Hedges 2008 Chap 5

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Detection of radioactivity

ionization detector- energy windows (each nuclide decay emits a characteristic energy spectrum (eg photons of gamma radiation) and can be distinguished from another)

Fission tracks

Scintillation counting (uses chemicals to absorb radiation energy leading to chain reactions that produce light Light pulses are detected with high sensitivity Again different nuclides can be distinguished based on energy of emission

Radiation is the amount of energy emitted

Radioactivity is a measure of nuclear disintegrations per unit time often given as disintegrations per minute (dpm)

Each time a nucleus decays it is an ldquoeventrdquo or disintegration

Common units of radioactivityCurie = 222 x 1012 disintegrations per minute (dpm) A curie is defined by the amount of radioactivity in 1 gram of Radium

In practice we commonly work in millicuries (222 x 109 dpm) or microcuries (222 x 106 dpm) or just plain dpm

Becquerel - The SI unit for radioactivity

1Bq = 1 disintegrationsec (dps)

So one Curie is = 37 x 1010 Becquerels (dps)

Specific activity ndash the amount of radioactivity per mole of substance eg mCimmol or dpmpmol

238U is the most abundant radionuclide in seawater

~3 g liter-1 mainly as uranyl tricarbonate [UO2(CO3)3]-4 which has uranium in the oxidized form U(+VI) [Uranium] is conservative with salinity

238U dpmliter = 007081 x salinity

In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Uranium (+VI) can be reduced by microbes under anoxic conditions adding 2 e- and producing U(+IV) This form is insoluble and precipitates Iron reducing bacteria can carry out this reduction (much interest in this)

At salinity = 35 238U activity = 248 dpmLiter of seawater

For nuclides in solution the chemical concentration (Nliter) is directly proportional to radioactivity per liter (Nliter) since

The absolute concentrations of many nuclides in seawater is very low and not easily measured by chemical means But their radioactivity can be measured

Emerson amp Hedges 2008 Chap 5Emerson amp Hedges 2008 Chap 5

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Common units of radioactivityCurie = 222 x 1012 disintegrations per minute (dpm) A curie is defined by the amount of radioactivity in 1 gram of Radium

In practice we commonly work in millicuries (222 x 109 dpm) or microcuries (222 x 106 dpm) or just plain dpm

Becquerel - The SI unit for radioactivity

1Bq = 1 disintegrationsec (dps)

So one Curie is = 37 x 1010 Becquerels (dps)

Specific activity ndash the amount of radioactivity per mole of substance eg mCimmol or dpmpmol

238U is the most abundant radionuclide in seawater

~3 g liter-1 mainly as uranyl tricarbonate [UO2(CO3)3]-4 which has uranium in the oxidized form U(+VI) [Uranium] is conservative with salinity

238U dpmliter = 007081 x salinity

In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Uranium (+VI) can be reduced by microbes under anoxic conditions adding 2 e- and producing U(+IV) This form is insoluble and precipitates Iron reducing bacteria can carry out this reduction (much interest in this)

At salinity = 35 238U activity = 248 dpmLiter of seawater

For nuclides in solution the chemical concentration (Nliter) is directly proportional to radioactivity per liter (Nliter) since

The absolute concentrations of many nuclides in seawater is very low and not easily measured by chemical means But their radioactivity can be measured

Emerson amp Hedges 2008 Chap 5Emerson amp Hedges 2008 Chap 5

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

238U is the most abundant radionuclide in seawater

~3 g liter-1 mainly as uranyl tricarbonate [UO2(CO3)3]-4 which has uranium in the oxidized form U(+VI) [Uranium] is conservative with salinity

238U dpmliter = 007081 x salinity

In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Uranium (+VI) can be reduced by microbes under anoxic conditions adding 2 e- and producing U(+IV) This form is insoluble and precipitates Iron reducing bacteria can carry out this reduction (much interest in this)

At salinity = 35 238U activity = 248 dpmLiter of seawater

For nuclides in solution the chemical concentration (Nliter) is directly proportional to radioactivity per liter (Nliter) since

The absolute concentrations of many nuclides in seawater is very low and not easily measured by chemical means But their radioactivity can be measured

Emerson amp Hedges 2008 Chap 5Emerson amp Hedges 2008 Chap 5

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

For nuclides in solution the chemical concentration (Nliter) is directly proportional to radioactivity per liter (Nliter) since

The absolute concentrations of many nuclides in seawater is very low and not easily measured by chemical means But their radioactivity can be measured

Emerson amp Hedges 2008 Chap 5Emerson amp Hedges 2008 Chap 5

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Emerson amp Hedges 2008 Chap 5Emerson amp Hedges 2008 Chap 5

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Secular equilibrium (daughter-parent relationships)

For a parent nuclide (P) with a long half life relative to its daughter nuclide (D) the activity of the Parent is given by

dPdt = P[P] and this is the production rate of the Daughter (since daughter is short lived its existence depends on its production from parent)

The rate of change of the Daughter nuclide is determined by its production and loss

dDdt = P[P] - D[D]

rate of change = Production - Loss (by radioactive decay)

At steady state

dDdt = 0 = P[P] - D[D]

P[P] = D[D] or Ap = AD or AD AP = 1

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Thus for nuclides with short-lived daughters and long lived parents one predicts that the daughterparent activity ratio ( AD AP) = 1 This situation is termed secular equilibrium For a system starting out with parent nuclide but no daughter AD will grow into the system In other words it takes time to reach secular equilibrium

Act

ivit

y Parent activity

Total activity(parent+daughter)

Time

It takes about 6-8 daughter half-lives to reach secular equilibrium

Parent activity is constant with time since very few atoms decay (because of long half life)

In-growth of daughter activity

Daughter activity becomes constant with time because Production = Loss

The activity of the daughter is supported by the parent

0

1

2

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Emerson amp Hedges Chap 5Emerson amp Hedges Chap 5

Changing the decay constant for daughter will change ND but not λND (if λ goes up ND goes

down and vice versa)

The rate of flow into the daughter tank λNP is equal to the flow out λND

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Deviations from secular equilibrium

If all nuclides were in secular equilibrium we couldnrsquot learn anything from them

The deviations from equilibrium are the basis for using the nuclides as tracers and chronometers

234Th activity in the water column is often less than its parent 238U because of scavenging which removes the daughter

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Any process that adds or removes daughter nuclide will cause deviations from secular equilibrium

The deviations from secular equilibrium can be used to estimate the scavenging rate constant (particle removal rate constant) in the ocean water column (see steady state box model calculations as used in Coale and Bruland 1987 LampO 32 189)

The ldquokrdquo here would be the scavenging rate constant (the fraction of particles exported from the surface ocean to depth per unit time Something very useful to know

d[D]dt = P[P] - D[D] + k[D]

Production of daughter Loss of daughter

Loss by rad decay

Other first order loss (eg scavenging)

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

y axis

x axis

Which nuclide to use

Must use a nuclide with a half-life close to the rate of the process of interest

Nuclides with short half lifes can only be used to study fast processes

Long-lived nuclides cannot be used to study fast processes (too few decays over short time) and only are useful for slow processes

This matching of decay rate to process rate applies to radio-dating (aging) as well

234Th (t12 = 24 d) is useful for water column particle scavenging rates

coastal oceanic

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Expected

Shaded area is deficit of 234Th due to scavening

Coale amp Bruland LampO 1987 ndash Application of Coale amp Bruland LampO 1987 ndash Application of 234234Th scavengingTh scavenging

Mixed layerpycnocline

Euphotic

bull Maximum scavenging near pigment maximum

bull Less scavenging in upper mixed layer (due to efficient recycling of particles amp biomass)

234234Th is particle reactive so most is rapidly adsorbed to Th is particle reactive so most is rapidly adsorbed to particles If particles sink quickly then have deficit of particles If particles sink quickly then have deficit of 234234Th Th

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Moran et al 2003 Limnol Oceanogr 48 1018

234Th-derived

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Radio-dating of materials with nuclides

Useful for determining the age of a particular piece of matter (organism fossil rock etc)

By obtaining an age for a piece of an accreting deposit (eg sediment coral skeleton clam shell Mn-nodule) at some depth into the deposit the accretion rates of deposit can be determined (assuming steady deposition)

If you can put an age on the sediment in this layer you therefore know how long it took to build up the sediment above it From the depth of the layer and its age (t) you can determine the sediment accretion rate (zt)

Depth z

Sediment core

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

How to determine ages in deposits

Use unsupported nuclide activities

If deposits are laid down with unsupported daughter activity and no additional inputs (other than supported activity) occur within the deposit then the unsupported (excess) activity will decay with time (=depth) into the deposit Sediment is a good example

20

0

Dep

th (

cm)

AD-excess (unsupported daughter)

Exponential Exponential decay of decay of excess excess activity with activity with depthdepth

The sedimentation or accretion rate is given by

s= zt Thus

t = zs or

t = zs

Substitute zs for t in decay law

Sediment-water interface

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

ADz = ADo e-λ(zs)

Where ADz is the unsupported activity at depth z and ADo is the unsupported activity at the surface of the deposit This can be rearranged to

ADzADo = e-λ(zs)

And linearized as

ln(ADz) ndash ln(ADo) = -λ(zs) which is the same as

ln(ADz) = ln(ADo) - λ(zs) and the same as

ln(ADz) = ln(ADo) ndash (λs) zX-coordinateslopeY-intercept

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

210Pb is derived from decay of gaseous 222Rn (t12 = 38 days) which originates in rocks on land but goes into the atmosphere where it is carried over water

210Pb produced in the atmosphere is rapidly rained out and it attaches to particles in the water which sink to the sediments

210Pb (t12 = 223 y) is often used to estimate sediment accretion rates in coastal areas where sedimentation is high

This leads to unsupported 210Pb activity at the surface of the sediment (activity ratio of 210Pb(daughter)226Ra(parent)

gt 1) This is also referred to as excess activity because it is in excess of what is supported by the secular equilibrium of the sedimentary 226Ra parent

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Concentrations of unsupported 210Pb in sediments ndash can give estimate of sediment accretion rates

Fig 107 in PilsonFig 107 in Pilson

Linear slope (a) of the semi-log plot gives the sediment accretion rate If slope not linear ndash steady state sedimentation model does not apply

Log

sca

le

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

(Bioturbated)

Supported 230 Th activity (from 234U decay)

Excess

This figure focuses on the longer lived nuclide 230Th (t12 = 75200 y) Its chemistry (ie particle reactivity) is the same as 234Th but its decay is too slow to be useful for particle scavenging rates in the surface waters It is however useful for sediment accretion rates in the deep ocean where accretion rates are relatively slow

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

137Cs

Peak emissions of man-made 137Cs (t12 = ~30 y) into the atmosphere occurred in 1963

This particle reactive nuclide is scavenged to sediments where profiles reflect time inputs Depth above 137Cs peak has accreted since 1963

Core taken

in 1986

~10 cm per 23 y

Use of nuclides as event markers

Wetland sedimentsDeLaune et al 1989

137Cs first appeared in atmosphere in ~1953

Picocuries per section

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Natural 14C- a cosmogenic nuclide

bull Produced in the upper atmosphere by spallation of 14N

bull Becomes 14CO2 in atmosphere

bull Dissolves in ocean and taken up by plants

bull Diluted by fossil fuel burning of low 14C carbon (Suess effect)

Man-made 14C

Produced from weapons testing ndash peak production in 1960rsquos

Increased atmospheric 14C by over 2x ndash slowly taken up by ocean

(Illustration by Jayne Doucette Woods Hole Oceanographic Institution)httpwwwwhoiedunosamspagedopid=40138

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Applications of 14C datingMuch progress with introduction of accelerator mass spectrometer analysis ndash 14C content of micro- to milligram quantities of carbon can be determined

bull Invasion of atmospheric CO2 into ocean can be observed

bull DIC of ocean water can be aged ndash giving estimate of deep residence time

bull POC and DOC in seawater have been aged ndash DOC found to be old

bull Bacteria in surface ocean use a mixture of old and new carbon 14C-content of natural materials (mg quantities) can be measured at the

National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)Facility at Woods Hole - httpwwwwhoiedunosams

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

14C-ages for compounds containing carbon

bull At the time of carbon fixation (photosynthesis) some 14C will be incorporated into organic matter based on the amount of 14C in the atmosphere (or seawater) at the time of fixation

bull Once an organism dies no replacement of 14C occurs therefore the 14C radioactivity can only decrease due to decay

bull Since the decay rate of 14C is known (1209 x 10-4 y-1) the deficit of 14C activity can tell us how much time has elapsed since that organic matter was alive

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

14C =(14CC)sample - (14CC)std x 1000 - IF

(14CC)std

Fractionation factor (a small correction)

A zero value for A zero value for ΔΔ1414C represents the C represents the 1414C content of preindustrial atmosphereC content of preindustrial atmosphere

From Bauer amp Bianchi 2011 Dissolved organic carbon cycling and transformation In A treatise on Estuarine and Coastal Science Vol 5 7-67

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

WOCE = World Ocean Circulation ExperimentWOCE = World Ocean Circulation Experiment

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Deep DOC ~5900 years old Deep DOC ~4100 years old

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Belize and Belize and Florida corals Florida corals

Galapagos Galapagos corals corals (upwelling (upwelling area)area)

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Estuarine SiteEstuarine Site

Oceanic SiteOceanic Site

From Cherrier et al 2000From Cherrier et al 2000

Bacterioplankton use mainly recently fixed carbon ndash but in the open ocean some older carbon from DOC is utilized also

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

EndEnd

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Age = -8033 ln (FmAge = -8033 ln (Fm13C corr13C corr))

S=S=1414CC1212C SampleC SampleB= B= 1414CC1212C BlankC BlankM = M = 1414CC1212C Modern referenceC Modern reference

Where lambda is 1(tru mean-life) of radiocarbon = 18267 = 000012097Yc is year of collection

Fraction Modern Fraction Modern

Fm is corrected to that of -25 ooo Fm is corrected to that of -25 ooo δδ1313C C

Res

iden

ce ti

me

=1

kR

esid

ence

tim

e =

1k

Large uncertainty in residence time or k

Large uncertainty in residence time or k

From Coale amp Bruland 1987From Coale amp Bruland 1987

238U -gt 234Th -gt-gt234U -gt 230Th -gt 226Ra -gt 222Rn -gthellip210Pb-gt-gt 206Pb

232Th -gt 228Ra -gt-gt 228Th -gt 224Ra -gt 220Rn -gt 216Po -gt hellip208Pb

235U -gt 231Th -gt 231Pa -gt-gt 227Th -gt 223Ra -gt 219Rn -gt hellip-gt 207Pb

Primordial decay series (three major parent nuclides)see Fig 102 in Pilson for decay chain and half lives of 238U series

All primordial series end with stable (non-radioactive) form of lead (Pb)

Parent Daughters

Stable end

product

In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Although the atom ratio of 238U235U is 140 the activity ratio is only 217 because 235U has a much shorter half-life than 238U (so a greater fraction of the 238U atoms are undergoing decay at any time)

This figure shows two shallow north-south sections from approximately the same area of the East Pacific depicting the C-14 concentrations measured 20 years apart Clearly visible is the evolution of the bomb C-14 signal (yellow-red) since the end of the nuclear bomb tests (top) to the present (top plot) especially at intermediate and high latitudes

httpwwwnosamswhoieduwocewocegeoshtml

1992

1974

• PowerPoint Presentation
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• 14C-ages for compounds containing carbon
• Slide 34
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238U -gt 234Th -gt-gt234U -gt 230Th -gt 226Ra -gt 222Rn -gthellip210Pb-gt-gt 206Pb

232Th -gt 228Ra -gt-gt 228Th -gt 224Ra -gt 220Rn -gt 216Po -gt hellip208Pb

235U -gt 231Th -gt 231Pa -gt-gt 227Th -gt 223Ra -gt 219Rn -gt hellip-gt 207Pb

Primordial decay series (three major parent nuclides)see Fig 102 in Pilson for decay chain and half lives of 238U series

All primordial series end with stable (non-radioactive) form of lead (Pb)

Parent Daughters

Stable end

product

In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Although the atom ratio of 238U235U is 140 the activity ratio is only 217 because 235U has a much shorter half-life than 238U (so a greater fraction of the 238U atoms are undergoing decay at any time)

This figure shows two shallow north-south sections from approximately the same area of the East Pacific depicting the C-14 concentrations measured 20 years apart Clearly visible is the evolution of the bomb C-14 signal (yellow-red) since the end of the nuclear bomb tests (top) to the present (top plot) especially at intermediate and high latitudes

httpwwwnosamswhoieduwocewocegeoshtml

1992

1974

• PowerPoint Presentation
• Slide 2
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• 14C-ages for compounds containing carbon
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In seawater

238U 9928 of total U based on the of atoms

235U 072

234U 00055

Although the atom ratio of 238U235U is 140 the activity ratio is only 217 because 235U has a much shorter half-life than 238U (so a greater fraction of the 238U atoms are undergoing decay at any time)

This figure shows two shallow north-south sections from approximately the same area of the East Pacific depicting the C-14 concentrations measured 20 years apart Clearly visible is the evolution of the bomb C-14 signal (yellow-red) since the end of the nuclear bomb tests (top) to the present (top plot) especially at intermediate and high latitudes

httpwwwnosamswhoieduwocewocegeoshtml

1992

1974

• PowerPoint Presentation
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
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• 14C-ages for compounds containing carbon
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This figure shows two shallow north-south sections from approximately the same area of the East Pacific depicting the C-14 concentrations measured 20 years apart Clearly visible is the evolution of the bomb C-14 signal (yellow-red) since the end of the nuclear bomb tests (top) to the present (top plot) especially at intermediate and high latitudes

httpwwwnosamswhoieduwocewocegeoshtml

1992

1974

• PowerPoint Presentation
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
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• 14C-ages for compounds containing carbon
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