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Agouron_PW_lecture_3
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THE OCEAN CARBON BUDGET: CAN WE MAKE SENSE FROM NONSENSE
A) THE STRUCTURE OF THE OCEANIC BUDGET
Atmosphere
Open oceanCoastal oceanLand
Marginal benthos
Estuaries
P/R cycleP/R cycle P/R cycle
P/R cycle
P/R cycle
P/R cycle Photosynthesis/respiration cycle
P/R cycleP/R cycle P/R cycle
P/R cycle
P/R cycle
P/R cycle
P/R cycleP/R cycleP/R cycleP/R cycle P/R cycleP/R cycle
P/R cycleP/R cycle
P/R cycleP/R cycle
P/R cycleP/R cycle Photosynthesis/respiration cycle
Organic fluxesOrganic fluxes
CO2 fluxesCO2 fluxes
Global Carbon Cycle
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SourceNet productionNet consumptionNet heterotrophicP<R
SinkNet consumptionNet productionNet autotrophicP>R
CO2source/sink
Net CO2 metabolism
Net O2 metabolism
Trophic stateP v R balance
SourceNet productionNet consumptionNet heterotrophicP<R
SinkNet consumptionNet productionNet autotrophicP>R
CO2source/sink
Net CO2 metabolism
Net O2 metabolism
Trophic stateP v R balance
The Biogeochemical Cycle – Closed System
Photosynthesis
CO2 + H2O = “CH2O” + O2
Respiration
All units are Tmol C/a
Light
Heat
The closed system cannot sustain P<R for extended periods as the organic reservoir in the oceans is small
P/R cycleP/R cycleP/R cycle
The Biogeochemical Cycle - Open Systems
General assumption is that the system is in some sort of steady state (the organic carrying capacity of the sea is very limited)
Thus, if P not equal to R there must be a net source or sink
Mass balance equation: P + I = R + E(where, I & E are Imports and Exports)
E & I are commonly easier to ascertain than P & R
Rearrange to: P - R = E - I
E>I, then P>R net autotrophicI>E, then R>P net heterotrophic
ImportsImports ExportsExports
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B) OVERALL MASS BALANCE
P/R cycleP/R cycle
Atmosphere
23 T
mol
C/a
23 T
mol
C/a
Net Heterotrophic ocean
P/R cycleP/R cycleP/R cycleP/R cycle
Estuaries
35 Tmol C/a35 Tmol C/a12 Tm
olC/a
12 TmolC
/a35 Tmol C/a35 Tmol C/a
43 T
mol
C/a
43 T
mol
C/a
23 Tmol C/a23 Tmol C/a
Conclusion:
Net autotrophic land feeding a
Net heterotrophic ocean
Terrestrial P/R cycle. 10,000 Tmol C/a
20 T
mol
C/a
CH420 T
mol
C/a
20 T
mol
C/a
CH4
5,85
0 Tm
olC
/a5,
850
Tmol
C/a
6,00
0 Tm
olC
/a6,
000
Tmol
C/a
Land Coastal ocean + Open ocean
All units are Tmol C/a
Mangroves Coral reefs
Macroalgae
Sea grasses
Marginal Benthic Ecosystems
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P & R balance in marginal benthic ecosystems (Duarte et al. 2005)
Export into the coastal zone = 860-(609+9.3) = 250 Tmol C/a
9.3609860
-166135Unvegetatedhabitats
-7986Coral Reefs-247432Macroalgae
2.31952Sea Grasses567120Salt marshes23135Mangroves
BurialTmol C/a
RespirationTmol C/a
PhotosynthesisTmol C/a
9.3609860
-166135Unvegetatedhabitats
-7986Coral Reefs-247432Macroalgae
2.31952Sea Grasses567120Salt marshes23135Mangroves
BurialTmol C/a
RespirationTmol C/a
PhotosynthesisTmol C/a
P + IR + IA + IC = R + ES + EA E-I
35 + 2 15 + 2 = -20 35 + 2 + 250 15 + 2 = -270
Thus, At P = R-20 Tmol C/a; the oceans are NET Heterotrophic Assume P ~ 5,000 to 10,000 Tmol C/a Percentage heterotrophy = 0.2 to 0.4%, well beyond field techniques to detect
Imports ExportsImportsImports ExportsExports
At P + = R - 270 Tmol C/a; t the oceans are NET Heterotrophic Assume P ~ 5,000 to 10,000 Tmol C/a Percentage heterotrophy = 2.5 to 5%, difficult for field techniques to detect
Imports ExportsImportsImports ExportsExports
287 27
37 27
R>R
R>R
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Wetlands
Net Autotrophic
Net Heterotrophic3500m
150m
1000m
Land
Sediments
SedimentsEpipelagic Ocean
Lakes
Bathypelagic Ocean
Sediments
Sediments
Mesopelagic Ocean
Coastal Zone
Estuaries
Atm
osph
ere
Rivers
SedimentsCoastal Margins
Net heterotrophy is a widespread and repeated observation in aquatic ecosystemsWhy? How?
See also Duarte and Prairie (2005) Prevalence of Heterotrophy and Atmospheric CO2 Emissions from Aquatic Ecosystems. Ecosystems 8 862-870
C) INTERNAL DISTRIBUTION - ANALYSIS OF FIELD OBSERVATIONS DISPARITY BETWEEN IN SITU AND IN VITRO OBSERVATIONS
del Giorgio, et al. (1997), Respiration rates in bacteria exceed plankton production in
unproductive aquatic systems. Nature 385, 148-151 Duarte, C. M. and Agusti, S. (1998), The CO2 balance of unproductive aquatic
ecosystems. Science. 281 234-236. Williams, P. J. le B. (1998), The Balance of Plankton Respiration and Photosynthesis
in the Open Oceans. Nature 394 55-57.
Fit to the equation R = aPb, which enables us to solve for P = R,
i.e. P=aPb, a = P/Pb = P(1-b), then P=a1/(1-b)
- 2
- 1
0
1
2
- 2 - 1 0 1 2L o g 1 0 ( P h o t o s y n t h e t ic R a t e )
Log 1
0(Res
pira
tion
rate
)
- 2
- 1
0
1
2
- 2 - 1 0 1 2
L o g 1 0 ( P h o t o s y n t h e t ic R a t e )
Log 1
0(R
espi
ratio
n ra
te)
N e t H e t e r o t r o p h y
N e t A u t o t r o p h y
R = PF i tte d L i n e
Agouron_PW_lecture_3
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Units
a as
gO2/m3d
b
P=R as
gO2/m3d
P=R as
mmolO2/m3 d
Observations
Del Giorgio et al., 1997
7.24 0.62 183 15 Only systems with net productivity >10 mmol C/m3 d are autotrophic. Most of the oceans fall below 10 mmol C/m3; surface values at HOTS are c. 1 mmol C/m3 d
Duarte & Agusti, 1998
Coastal water 1.1 0.72 1.62 44
Ocean water 0.2 0.5 0.035 1.25
Overall oceans 0.27 0.615 0.033 1.04
The oceans as a whole are in metabolic balance i.e. ΣP=ΣR. 25 out of Longhurst’s 56 biogeochemical zones (80% ocean surface) are net heterotrophic, sustained by the remaining 20% of the ocean surface
Williams, 1998 No correlation – r2 = 0.07
P=R at rates way beyond those observed
There is no evidence for the large regional imbalances
Autotrophic zones: Heterotrophic zones:
The Predicted Distribution of Autotrophy and Heterotrophy from the Duarte & Agusti Equation
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The Problem The Prediction Calculated Annual Net Production = -8 mol C/m2d The Observation In situ rates (see table below) c. +3 mol C/m2d
Author Approach Annual Net Production (mol C m-2 a-1)
Emerson et al (1997) Surface oxygen budget +2.7±1.7
Benitez-Nelson et al (2001) Organic carbon export rates, based on 234Th budget, DOC gradients and zooplankton migration rates
+2.4±0.9
Sonnerup et al (1999) Subsurface O2 utilisation rates +2.2±0.5
Quay and Stutsman (2003) DIC and δ13C measurements +2.7±1.3
Juranek and Quay (2005) 18O2 and O2/Ar ratios +3.2
D) ACCOUNTING FOR THE IMBALANCES The imbalance can be derive from
1. Sampling & Interptetation (Williams) 2. Missed Organic Sources (Duarte) 3. Errors in in vitro Method (Williams)
1) Sampling & Interptetation
Spatial Depth – P>R at the surface, R>P at depth Regional – transfers between productive and unproductive zones
Temporal – Seasonal – accumulation of DOC in the productive period Subsampling – bursts of photosynthesis, integration by respiration
Spatial – depth (Williams, 1998)
y = 0.4107x - 0.0729R2 = 0.6287
-0.8
-0.6
-0.4
-0.2
0
0.2
-1.2 -0.8 -0.4 0
Log Photosythetic rate (mmolsO2/m3d)
RespP=R line
Log
Res
pira
tion
rate
(mm
olsO
2/m
3d)
Analysis of P vrs R for Station Aloha
020406080
100120140160
0 0.01 0.02 0.03
Rate
Dep
th (m
)
GPP
Resp
P and Predicted R values
0
20
40
60
80
100
120
-0.5 0 0.5 1 1.5
Rates (mmol O2/m3d)
Dep
th (m
)
GPPCal RespNCP
Agouron_PW_lecture_3
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Temporal – seasonal (Serret et al 1999)
Algal Photosynthesis and Community Respiration ( 30% Algal)
0
50
100
150
0 100 200 300 400Day of Year
Rat
es
Photosynthesis
Respiration
P/R ratio through a bloom rise and fall
0
10
20
30
40
50
0 25 50 75 100Photosynthetic Rate
Res
pira
tion
Rat
e
P/R ratio through a bloom rise and fall
0
1
2
0 1 2Log Photosynthetic Rate
Log
Res
pira
tion
Rat
e
Seasonal DOC accululationDOC formation Microbial recycling
Bloom P>R
Spring/Summer
Regeneration R>P
Autumn/Winter
HOT study (Williams et HOT 2004)
There appears to be no seasonal storage in the DOC component.
-2.0
-1.0
0.0
1.0
2.0
-2.0 -1.0 0.0 1.0 2.0
Log10(photosynthetic rate)Lo
g 10(
resp
iratio
n ra
te)
1:1 LineOLSMRA
y = 0.41xP + 0.1y = 0.62xP + 0.04
Photosynthesis vrs Respiration Volumetric data (1931 observations)
R2 = 0.44
0.5
1
1.5
2
2.5
3
0.5 1 1.5 2 2.5 3
Log10 (Σphotosynthetic rate) as mmoles m-2 d-1
Log1
0 (
resp
irato
ry ra
te) a
s m
mol
es m
-2 d
-1
1:1 lineOrdinary least squaresMajor reduced axis
Photosynthesis vrs RespirationAreal data (218 observations)
R2 = 0.072
Seasonal Cycle of Depth-integrated Rates
-100
-50
0
50
100
HO
T 12
6 ( 1
6/05
/200
1)
HO
T 12
7 ( 1
4/06
/200
1)
HO
T 12
8 ( 1
1/07
/200
1)
HO
T 12
9 ( 0
8/08
/200
1)
HO
T 13
1 ( 2
3/10
/200
1)
HO
T 13
2 ( 1
7/11
/200
1)
HO
T135
( 21
/02/
2002
)
HO
T136
( 13
/03/
2002
)
HO
T 13
7 ( 2
1/05
/200
2)
Rat
es (m
mol
m-2
d-1
)
GPP Depth IntegralNCP Depth IntegralResp Depth Integral14C Rate Integral
Seasaonal Profile of DOC (0-150m)
020406080
100120140
0 2 4 6 8 10 12Month
DO
C (u
M)
Agouron_PW_lecture_3
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Temporal – subsampling frequency (Karl, D.,et al. 2003)
2) Missed Sources Regional – transfers between productive and unproductive zones – Duarte’s perception (Duarte and Agusti, 1998).
Do we have a Autotrophic Coastal Ocean Subsidising Heterotrophic Open Ocean
Early Work (pre-1990) suggested this was so:
Steele (1974) and Walsh et al’s(1988) work suggested some 45% of coastal oceanic production was exported
But the conceptual models were flawed as they omitted microbial respiration
Williams, P. J. le B. and Bowers, D. G. (1999) Regional carbon imbalances in the
oceans. Science 284 1735b. Duarte, C. M., Agusti S, del Giorgio, P. A., and Cole, J. J . (1999) Regional carbon
imbalances in the oceans. Science 284 1735b.
Autotrophic zones: Heterotrophic zones:
Agouron_PW_lecture_3
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Transport of DOC & POC DOC i) The DOC from the rivers (c. 18 Tmol C/a) is
generally assumed to pass through the coastal zone to the open ocean unmodified
ii) From inshore/offshore DOC gradients Duarte estimates a offshore flux of 450 Tmol C/a flux (20x greater) –
POC moves down the continental slope into the mesopelagic: Wollast - 182 T mol C/a; Ducklow & McCallister - 100-200 T mol C/a
Atmospheric Transport (Dachs et al., 2005)
-32 -30 -28 -26 -24 -22 -20 -18 -16 -1416
18
20
22
24
26
28
-145-70
-99-39-51-43
-124-57
-112
-81 -58-138 -91
-210 -243
64
1967
7819437426
133
78 63 94 76 64192
386
602
179
13
77
6
-258
-611
-140
-15
-49
-36
28
26
24
oN 22
20
18
16-32 -30 -28 -26 -24 -22 -20 -18 -16 -14
oW
-32 -30 -28 -26 -24 -22 -20 -18 -16 -1416
18
20
22
24
26
28
-145-70
-99-39-51-43
-124-57
-112
-81 -58-138 -91
-210 -243
64
1967
7819437426
133
78 63 94 76 64192
386
602
179
13
77
6
-258
-611
-140
-15
-49
-36
28
26
24
oN 22
20
18
16-32 -30 -28 -26 -24 -22 -20 -18 -16 -14
oW Estimates range:
coastal regions - mean uptake of c.500 m moles C m-2 d-1
- mean emission of 440 m moles C m-2 d-1
With a mean for the region of 28 m moles C m-2 d-1 ≡ 120gC m-2 a-1
Which is massive, considering productivity rates may be in the region of 150-300 gC m-2 a-1
Total emission = 0.64 Gt C yr = 50 Tmol (C/a 50x1012 mol C/a)
Raises the question: where does it come from: it’s 10% of fossil fuel consumption
Agouron_PW_lecture_3
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3) Errors in in vitro Methodology We are getting repeated and reliable reports of in situ O2-determined rates, far exceeding in vitro 14C and ∆O2 determined rates that we need to look hard at our methodology a) So called “Bottle effects” b) Incubation procedures E) BALANCING THE OCEANIC BUDGET Problems in a number of related areas: 1) Discrepancies in the Global Estimate of P and R 2) Different Conclusions over the distribution of P-R balance within the Oceans 3) Wide range of estimated of the transport between various pools
1) Discrepancies in the Global Estimate of P and R a. Methodological errors in estimating P (& possibly R) b. Small, and probably biased, database for R
Coastal ocean + Open oceanLand
P/R cycle
35 Tmol C/a
Coastal ocean + Open oceanLand
P/R cycle
35 Tmol C/a35 Tmol C/a
A c.10,000 T mol C/a deficit (75% of turnover) would suggest a major budgetary problem! Respiration (O2) = 13,000 T mol C/a
Photosynthesis (14C) = 3,500 T molC/a
12 Tmol/a
12 Tmol/aOne/both of our methods is giving the wrong answer
1) Errors in the interpreting the 14C-technique and global projection: x2-x3
2) O2 data-base too small for accurate global estimates
Geochemical estimates (16O2/17O2/18O2 disequilibrium and O2 flux) suggest higher figure is more probable
Agouron_PW_lecture_3
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Errors Associated with the 14C-technigue
With the 14C technique we are not comparing like with like:
1) We should be comparing total photosynthesis (GPP) with total respiration (R)
The 14C-algal measures something between GPP and NPP (perhaps even NCP)NPP = GPP – Ralgal
So we are comparing: GPP – Ralgal with Ralgal+ Rheterotroph
As algal respiration through the water column is c. 40% of GPPwe get a substantial error
2) Loss of DOC by excretion is overlooked
We can attempt to make corrections:1) Algal respiration at high P rates algal R≈0.1*P, but through the
water column euphotic zone R≈0.4*P is probably a reasonable estimate
2) Estimates of excretion are commonly believed to be ≈0.15*P, but figures ≈0.5 *P have been suggested
@ 15% Exc=0.15*P & R=0.4*P; 2,500 T mol C a-1 converts to 4,900 T mol C a-1
@ 50% Exc=0.50*P & R=0.4*P; 2,500 T mol C a-1 converts to 8,300 T mol C a-1
Thus we can make some headway to match a respiration figure of 13,000 mol C a-1, but we need to make some uncomfortably extreme assumptions
At best it only can account for part of the solution
2) The O2 respiration database is too small to attempt global estimates
Conclusions
Global Distribution of Respiration Measurements (white dots)
Global Distribution of Respiration Measurements (white dots)
No Data
No Data
No DataNo
Data
No Data
No Data
No Data
No Data
The Current (as of 2004) Respiration Data base
Agouron_PW_lecture_3
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Low estimate High estimate Geomean T mol C/a T mol C/a T mol C/a COASTAL ZONE INPUT INTO COASTAL REGIONS Rivers 35 35 35 Atmosphere 1.5 250 (net) 20 Marginal benthos 1 250 16 OUTPUTS FROM COASTAL ZONE Atmosphere 1 1 1 Sediments 9 15 12 Ocean - Epipelagic 18 450 90 Ocean - Mesopelagic 1 180 13 PRIMARY PRODUCTION 600 1200 850 EPIPELAGIC OPEN OCEAN INPUTS INTO EPIPELAGIC OCEAN Coastal zone 18 450 100 Atmosphere 1 250 20 OUTPUTS FROM EPIPELAGIC OCEAN Atmosphere 1 1 1 Mesopelagic 100 500 225 PRIMARY PRODUCTION 3,500 10,000 600 MESO+BATHY-PELAGIC OPEN OCEAN INPUTS INTO THE MESOPELAGIC Coastal Zone 1 450 20 Epipelagic 100 500 225 OUTPUTS FROM BETHYPELAGIC Sediments 2 2 2
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LOW ESTIMATESAtmosphere Atmosphere
1.5 1.5 1 1Margins 1
Coastal 18 EpipelagicRivers 35 Balance 8 Balance -82
Net hetero 1% Net auto -2%1 100 Mesopelagic
9
2Sediments
Coastal Zone Open Ocean
Sediments
HIGH ESTIMATES
Atmosphere Atmosphere250 1 250 2
Margins 250
Coastal 450 EpipelagicRivers 35 Balance -113 Balance 248
Net auto -9% Net hetero 2%182 450 Mesopelagic
15
2Sediments
Sediments
Coastal Zone Open Ocean GEOMETRIC MEAN ESTIMATES
Atmosphere Atmosphere20 1 20 2
Margins 16
Coastal 90 EpipelagicRivers 35 Balance -45 Balance -107
Net auto -5% Net auto -2%13 225 Mesopelagic
12
2Sediments
Sediments
Coastal Zone Open Ocean
Summary of Mass Balances ESTIMATE COASTAL ZONE UPPER OPEN OCEANLOW Net Hetero (1%) Net Auto (2%) HIGH Net Auto (9%) Net Hetero (2%) GEOMEAN Net Auto (5%) Net Auto (2%)
Agouron_PW_lecture_3
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Essential reading:
del Giorgio, et al. (1997) Respiration rates in bacteria exceed plankton production in unproductive aquatic systems. Nature 385, 148-151
Duarte, C. M. and Agusti, S. (1998) The CO2 balance of unproductive aquatic ecosystems. Science. 281 234-236.
Williams, P. J. le B. (1998) The Balance of Plankton Respiration and Photosynthesis in the Open Oceans. Nature 394 55-57.
Supplementary reading: Duarte and Prairie (2005) Prevalence of Heterotrophy and Atmospheric CO2
Emissions from Aquatic Ecosystems. Ecosystems 8 862-870 Serret et al (1999) Seasonal compensation of microbial production and
respiration in a temperate sea. MEPS 187 43-57 Williams, Peter J. le B., Morris Paul J and. Karl David M (2004) Net
Community Production and Metabolic Balance at the Oligotrophic Ocean Site, Station ALOHA. Deep Sea Res 51: 1563-1578
Karl, D.,M., Laws, E. A., Morris, P, J., Williams, P. J. le B and Emerson S. (2003) Metabolic balance in the sea. Nature 426 32