The Southern Ocean sink for atmospheric CO2

Nicolas Gruber(1), S. Fletcher-Mikaloff(1), A. Jacobson(2), M. Gloor(2), J.L. Sarmiento(2)

(1) Department of Atmospheric and Oceanic Sciences & IGPP, UCLA(2) AOS Program, Princeton University

Takahashi et al. (2002) u2 a la Wanninkhof et al. (2001)

TWO VIEWS OF CO2 FLUXES IN THE SOUTHERN OCEAN

TRANSCOMGurney et al. (2002)

• Basis functions are model simulated footprints of unit emissions from a number of fixed regions

• Estimate linear combination of basis functions that fits observations in a least squares sense.

Inversion is analogous to linear regression

footprints fluxes obs

Premultiply both sides by inverse of A

INVERSION OF OCEAN INTERIOR OBSERVATIONS AS A CONSTRAINT ON CO2 FLUXES

estimated fluxes

OCEAN INVERSION RESULTS

COMPARISON WITH TAKAHASHI AND TRANSCOM

MODEL SENSITIVITY

DATA: Cant and Cgasex

Cgasex = DICobs - Cbio - Cant - const

Gruber et al., (1996) Gruber and Sarmiento (2002)

Cant : estimated by C* method

Summary

• Our inversion of ocean interior Cant and Cgasex data suggests

that the Southern Ocean south of 44ºS is currently about

neutral with regard to the atmosphere.

• This neutral flux is due to a compensation between outgassing

of natural CO2 and uptake of anthropogenic CO2.

• Our inversion results suggest a weaker Southern Ocean sink

for atmospheric CO2 than inferred by Takahashi et al. (2002).

Possible reasons for the discrepancy are:

- inversion biases (model transport, data)

- summer bias of pCO2 data

Pre-industrial CO2 fluxes

THE CHANGE OF SOUTHERN OCEAN CO2 FLUXES OVER TIME

1995 CO2 fluxes

(mol m-2 yr-1)

KVLOW-AILOW model

Pre-industrial CO2 fluxes

NATURAL VS ANTHROPOGENIC CO2 FLUXES IN THE SOUTHERN OCEAN

1995 Anthropogenic CO2 fluxes

(mol m-2 yr-1)

KVLOW-AILOW model