Quaternary EnvironmentsQuaternary EnvironmentsIce CoresIce Cores

Records From Ice CoresRecords From Ice Cores

PrecipitationPrecipitation Air TemperatureAir Temperature Atmospheric CompositionAtmospheric Composition

Gaseous compositionGaseous composition Soluble and insoluble particlesSoluble and insoluble particles

Volcanic EruptionsVolcanic Eruptions Solar ActivitySolar Activity

Records From Ice CoresRecords From Ice Cores

Extent of Ice Core SamplingExtent of Ice Core Sampling

15 Ice cores extend into the last glaciation15 Ice cores extend into the last glaciation GreenlandGreenland AntarcticaAntarctica ChinaChina Few Mid-Latitude high elevation coresFew Mid-Latitude high elevation cores

Paleoclimatic Information From Ice Paleoclimatic Information From Ice CoresCores

Stable isotopes of water and the Stable isotopes of water and the atmospheric Oatmospheric O22

Other gases from air bubbles in the iceOther gases from air bubbles in the iceDissolved and particulate matter in firn and Dissolved and particulate matter in firn and

iceiceThe physical characteristics of the firn and The physical characteristics of the firn and

iceice

DefinitionsDefinitions

Snow CrystalsSnow Crystals – Form of snow as it falls – Form of snow as it falls FirnFirn – Snow that has survived the summer – Snow that has survived the summer

ablation seasonablation season IceIce – The produce of metamorphosis as firn is – The produce of metamorphosis as firn is

buried by subsequent snow accumulationburied by subsequent snow accumulation Depth varies depending upon surface temperature Depth varies depending upon surface temperature

and accumulation rateand accumulation rate i.e 68m at Camp Century, Greenland and 100m i.e 68m at Camp Century, Greenland and 100m

Vostok, AntarcticaVostok, Antarctica

Stable Isotope AnalysisStable Isotope Analysis

Basic Premise – Molecules with heavier isotopes Basic Premise – Molecules with heavier isotopes will stay at the source during evaporationwill stay at the source during evaporation HDHD1616O or HO or H22

1818OO

Various things control isotopic concentrationVarious things control isotopic concentration TemperatureTemperature EvaporationEvaporation Distance from sourceDistance from source

Compared to the Standard Mean Ocean Water Compared to the Standard Mean Ocean Water (SMOW) (SMOW) Equivalent to water collected from 200-500m depth in Equivalent to water collected from 200-500m depth in

the Atlantic, Pacific, and Indian Oceansthe Atlantic, Pacific, and Indian Oceans

ComplicationsComplications

1818O content of precipitation depends on:O content of precipitation depends on: 1818O content of water vapor from the sourceO content of water vapor from the source Amount of moisture in the air at sourceAmount of moisture in the air at source Evaporation en route to depositionEvaporation en route to deposition Source of land evaporationSource of land evaporation Temperature at which evaporation and Temperature at which evaporation and

condensation takes placecondensation takes place Extent to which clouds become supersaturatedExtent to which clouds become supersaturated

Empirical EvidenceEmpirical Evidence

Studies show that despite the complications Studies show that despite the complications geographical and temporal variations in geographical and temporal variations in isotopes do occur, reflecting temperature isotopes do occur, reflecting temperature effects due to changing effects due to changing latitudes, latitudes, altitude, altitude, distance from moisture source, distance from moisture source, season,season, long-term climatic fluctuations.long-term climatic fluctuations.

Dating of Ice Cores Dating of Ice Cores

Determine the age-depth relationshipDetermine the age-depth relationship Very accurate time scales for at least 10,000 to Very accurate time scales for at least 10,000 to

12,000 years12,000 years Radioisotopic MethodsRadioisotopic Methods

1010BeBe 1414C*C* 3939ArAr 8181KrKr 210210Pb*Pb*

Dating of Ice Cores Dating of Ice Cores

AMSAMS 14 14C DatingC Dating COCO22 from air bubbles from air bubbles 10kg of sample10kg of sample Equivalent to 1.5m length of ice coreEquivalent to 1.5m length of ice core

ProblemsProblems COCO22 exchange with the atmosphere is an open exchange with the atmosphere is an open

system until the air bubbles are cut off from the system until the air bubbles are cut off from the surfacesurface

Annual LayersAnnual Layers

Can count visual annual fluctuation in the Can count visual annual fluctuation in the ice caused by melt and thaw layersice caused by melt and thaw layers Various MarkersVarious Markers

Visual stratigraphyVisual stratigraphy Electrical conductivity measurements (ECM)Electrical conductivity measurements (ECM) Laser light scattering (from dust)Laser light scattering (from dust) Oxygen isotopesOxygen isotopes Chemical variationsChemical variations

GISP2 and GRIP match back to 15,000 GISP2 and GRIP match back to 15,000 years with 200 year precisionyears with 200 year precision

ResolutionResolution

<1% error back to 2,000 BP, <1% error back to 2,000 BP, 2% by 40,000 BP, 2% by 40,000 BP,

10% by 57,000 BP, 10% by 57,000 BP, up to 20% by 110,000 BPup to 20% by 110,000 BP

Seasonal VariationsSeasonal Variations

Microparticulate matter and ice chemistryMicroparticulate matter and ice chemistry Major ionsMajor ions Trace elementsTrace elements High Spring values and low Autumn values High Spring values and low Autumn values

produce seasonal variationsproduce seasonal variations Sodium, Calcium, Nitrate, ChlorideSodium, Calcium, Nitrate, Chloride

Electrical Conductivity Measurements Electrical Conductivity Measurements (ECM)(ECM) Continuous record of acidityContinuous record of acidity

Volcanic eruptions – highVolcanic eruptions – high Alkaline dust – low Alkaline dust – low

Changing resolution back in time from the Camp Century ice core from Greenland

Site A, Central Greenland

Electrical Conductivity MeasurementsElectrical Conductivity Measurements

Acidity of annual layers from A.D. 553 Acidity of annual layers from A.D. 553 to A.D. 1972to A.D. 1972

Accumulation at Summit, Accumulation at Summit, GreenlandGreenland

Theoretical ModelsTheoretical Models

Calculated ice-age at depth by means of a Calculated ice-age at depth by means of a theoretical ice-flow modeltheoretical ice-flow model Depend uponDepend upon

Past changes in ice thicknessPast changes in ice thickness TemperatureTemperature Accumulation ratesAccumulation rates Flow patternsFlow patterns And ice rheologyAnd ice rheology

Problems minimized at ice divides (Grip core at Problems minimized at ice divides (Grip core at Summit, Greenland) or deep cores that are still Summit, Greenland) or deep cores that are still well above ground level (Vostok, Antarctica)well above ground level (Vostok, Antarctica)

Schematic Diagram of Isotopic Schematic Diagram of Isotopic DepletionDepletion

Stratigraphic CorrelationsStratigraphic Correlations

Correlation of multiple proxy records from Correlation of multiple proxy records from ice cores against records with better ice cores against records with better chronological control (i.e. chronological control (i.e. δδ1818O from O from benthic foraminifera)benthic foraminifera)

Danger of correlating events and onset of Danger of correlating events and onset of circular reasoningcircular reasoning

Vostok Core, AntarcticaVostok Core, Antarctica Longest well-resolved ice-core record on Earth Longest well-resolved ice-core record on Earth

and a yardstick for comparison with other and a yardstick for comparison with other paleoclimatic recordspaleoclimatic records

Deuterium records compared with SPECMAP Deuterium records compared with SPECMAP δδ1818O records suggest that the Vostok core O records suggest that the Vostok core extend back 426,000 years spanning the last extend back 426,000 years spanning the last four glacial eventsfour glacial events SPECMAP DataSPECMAP Data

(1) quantitative data on planktonic species and assemblages (1) quantitative data on planktonic species and assemblages which reflect conditions in the surface waters of the Atlantic which reflect conditions in the surface waters of the Atlantic ocean; ocean;

(2) measurements of (2) measurements of 18180, 0, 1313C difference (planktonic and C difference (planktonic and benthic), and Cd/Ca. benthic), and Cd/Ca.

Climate ChangesClimate Changes

The rate and cause of climatic changes is The rate and cause of climatic changes is of great interestof great interest Resolution is an important factor in Resolution is an important factor in

determining rates of changedetermining rates of change

Shear in Ice RecordsShear in Ice Records Differential forces at depth in the glaciers Differential forces at depth in the glaciers

cause the ice to flow distorting the recordcause the ice to flow distorting the record Boudinage – Pinching of a layer that is Boudinage – Pinching of a layer that is

less likely to flow compared to the less likely to flow compared to the surrounding layerssurrounding layers Ice strength is dependent upon dust contentIce strength is dependent upon dust content

Atmospheric CompositionAtmospheric Composition

Ice cores are archives of atmospheric Ice cores are archives of atmospheric compositioncomposition Contain records of greenhouse gasesContain records of greenhouse gases

Carbon Dioxide, Methane, Nitrous OxideCarbon Dioxide, Methane, Nitrous Oxide

Air mass CharacteristicsAir mass Characteristics Volcanic EruptionsVolcanic Eruptions Changes in Dust contentChanges in Dust content

Greenhouse GasesGreenhouse Gases

Methane is 220% greater today than 250 Methane is 220% greater today than 250 years agoyears ago

Carbon Dioxide is 130% pre-industrial Carbon Dioxide is 130% pre-industrial levelslevels

Nitrous Oxide is 110% greater than 250 Nitrous Oxide is 110% greater than 250 years agoyears ago

All levels are far higher than anything All levels are far higher than anything seen in the last 220,000 yearsseen in the last 220,000 years

Volcanic Eruptions from Ice CoresVolcanic Eruptions from Ice Cores