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Agouron_PW_lecture_3

1/15

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


2/15

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


3/15

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


6/15

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


7/15

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


8/15

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)


9/15

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:


10/15

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


11/15

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


12/15

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


13/15

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


14/15

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%)


15/15

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

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