The Southern Ocean sink for atmospheric CO 2

1. The Southern Ocean sink for atmospheric CO2 Nicolas Gruber(1), S. Fletcher-Mikaloff(1), A. Jacobson(2), M. Gloor(2), J.L. Sarmiento(2) Department of Atmospheric and Oceanic Sciences & IGPP, UCLA AOS Program, Princeton University

2. TWO VIEWS OF CO2 FLUXES IN THE SOUTHERN OCEAN Takahashi et al. (2002) u2 a la Wanninkhof et al. (2001) TRANSCOM Gurney et al. (2002)

3. INVERSION OF OCEAN INTERIOR OBSERVATIONS AS A CONSTRAINT ON CO2 FLUXES • 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 estimated fluxes

4. OCEAN INVERSION RESULTS

5. COMPARISON WITH TAKAHASHI AND TRANSCOM

6. MODEL SENSITIVITY

7. DATA: DCant and DCgasex DCgasex = DICobs - DCbio - DCant - const DCant : estimated by DC* method Gruber et al., (1996) Gruber and Sarmiento (2002)

9. Summary • Our inversion of ocean interior DCant and DCgasex 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 DpCO2 data

10. THE CHANGE OF SOUTHERN OCEAN CO2 FLUXES OVER TIME (mol m-2 yr-1) Pre-industrial CO2 fluxes 1995 CO2 fluxes KVLOW-AILOW model

11. NATURAL VS ANTHROPOGENIC CO2 FLUXES IN THE SOUTHERN OCEAN (mol m-2 yr-1) Pre-industrial CO2 fluxes 1995 Anthropogenic CO2 fluxes KVLOW-AILOW model