Ralph KeelingScripps Institution of Oceanography

Global oceanic and land carbon sinks from the Scripps flask sampling

networks

Ocean CO2 uptake: H2O + CO2 + CO3

= ↔ 2HCO3

-

Land photosynthesis & respiration

Fossil-fuel burningB F

O

ΔCO2 = F – O – B

Atmospheric CO2 budget

Ocean CO2 uptake: H2O + CO2 + CO3

= ↔ 2HCO3

-

Land photosynthesis & respiration:CO2 + H2O ↔ O2 + H2O

Fossil-fuel burning: CHy + (1+y/4)O2 → CO2 + (y/2)H2O

B F

O

ΔCO2 = F – O – BΔO2 = -1.4F + 1.1B

Atmospheric CO2 and O2 budgets

Ocean CO2 uptake: H2O + CO2 + CO3

= ↔ 2HCO3

-

Land photosynthesis & respiration:CO2 + H2O ↔ O2 + H2O

Fossil-fuel burning: CHy + (1+y/4)O2 → CO2 + (y/2)H2O

B F

O

Atmospheric CO2 and O2 budgets

Z

ΔCO2 = F – O – BΔO2 = -1.4F + 1.1B + Z

Time Outgas Ocean Land Period Corr. Sink Sink

Manning (2001) 1990-2000 0.10 1.68±0.5 1.44±0.7 & IPCC(2001)

Keeling & 1990-2000 0.28 1.86 ± 0.6 1.26±0.8Garcia (2002)

Manning & 1993-2003 0.48 2.24 ± 0.61 0.51±0.74Keeling (2005,submitted)

Units: Pg C yr-1

Recent O2 based Carbon budgets

Time Outgas Ocean Land Period Corr. Sink Sink

Manning (2001) 1990-2000 0.10 1.68±0.5 1.44±0.7 & IPCC(2001)

Keeling & 1990-2000 0.28 1.86 ± 0.6 1.26±0.8Garcia (2002)

Manning & 1993-2003 0.48 2.24 ± 0.61 0.51±0.74Keeling (2005,submitted)

Units: Pg C yr-1

Recent O2 based Carbon budgets

Increase in estimated ocean sink results from (1) Upwards revision of outgassing correction, as indicated. (2) Observed O2 loss rate higher over 2000-2003 period.

year

77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03

10

14 m

ol

yr-1

0

2

4

6

Atmospheric O2

pe

r m

il y

r-1-0.08-0.040.000.04

Atmospheric 13C

Atmospheric CO2

b

SO

I

-4

0

4

Southern Oscillation Index

c

77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03

101

4 mo

l yr

-1

-12

-10

-8

-6

-4

d

a

Interannual variations in CO2 O2/N2 and 13C/12C

Correlations between CO2, δ13C, and O2 imply land dominance of variabilityon El Nino time scales

Discussion:

Dominance of land to interannual variability also supported by atmospheric inversions. This is now beyond dispute.

Nevertheless, the smaller oceanic contribution to variability remains poorly resolved. All available approaches have problems:

CO2 Inversions: can’t distinguish well between coastal oceans and landfluxes.

13C/12C: complicated by possible variations in isotopic fractionation factor with land biota changes.

O2: complicated by interannual variations in air-sea O2 exchange.

Discussion, continued:

Measurements of O2 nevertheless may prove helpful, by providing a test of ocean models that predict CO2 variability. The test is realizable via the tracer APO = O2 + 1.1 CO2

ΔCO2 = F – O – BΔO2 = -1.4F + 1.1B + Z ΔO2 +1.1 ΔCO2 = -0.3F -1.1O + Z

Interannual variability in APO should reflect interannual variability in the combined air-sea CO2 and O2 flux, since interannual variability in fossil-fuel burning (F) is small.

Z = Air-sea O2 flux

Observed versus Modeled variations in APO

Summary of findings:

Relatively good model-to-model agreement.

Observations show ~ ~2x more variability.

If models underestimate APO variability, do they also underestimate CO2 variability? Needs more work to resolve.

Acknowledgements

Charles D KeelingAndrew ManningRoberta HammeBill PaplawskyGalen McKinleyMick Follows Corinne LeQuereChristian Roedenbeck Laurent Bopp

Ocean biogeochem. ModelsMPI Jena modelAuthors: Buitenhuis, LeQuere, RodgersPhysics: OPA-ORCABio model: Dynamic Green Ocean typeForcing: daily NCEPResolution: 0.5°x2° tropics and poles 2°x2° sub-tropicsGas exchange: Liss and Merlivat

IPSL model Authors: Bopp, RodgersPhysics: OPA-ORCABio model: Dynamic Green Ocean type Forcing: daily NCEP, mixed boundary conditionsResolution:0.5°x2° tropics and poles 2°x2° sub-tropicsGas exchange: Wanninkhov (1992)

MIT model Authors: McKinley, Follows, MarshallPhysics: MITgcm-ECCOBiogeo: phosphate & light based exportForcing: 12 hr NCEPResolution: 1°x1° extra-tropics 0.3°x1° tropicsGas exchange: Wanninkhov (1992)

Global APO changes