1. Surface Ocean pCO 2 and Air-Sea CO 2 -exchange in Coupled Models Birgit Schneider 1*, Laurent Bopp 1, Patricia Cadule 1, Thomas Frölicher 2, Marion Gehlen 1, Fortunat Joos 2, Corinne Le Quéré 3 and Joachim Segschneider 4 1 Laboratoire des Sciences du Climat et de L‘Environnement (LSCE), Gif-sur- Yvette, France 2 Division of Climate- and Environmental Physics, University of Bern, Bern, Switzerland 3 University of East Anglia, Norwich, UK 4 Max-Planck-Institut für Meteorologie, Hamburg, Germany *birgit.schneider@lsce.ipsl.fr

2. Outline 1. How good are the models in simulating surface ocean pCO 2 and Air-Sea CO 2 -exchange? -> climatological fields: compared to the new Takahashi 2007 data base and OCMIP-2 model output -> interannual variability: compared to observations and output from a forced model -> temporal trends: compared to observations 2.How good are the models reproducing temporal variability of marine biological production? ->interannual variability: compared to observation-based estimates derived from satellite data

3. Models and Experiments All models have been treated according to the C4MIP protocol. (Friedlingstein et al., 2006) Period investigated: 1985-2005 IPSLMPIMNCAR ocean modelOPA 8MPIOMNCAR-CSM1.4 hor. resolutionORCA 2° x 2°x cos lat1.5° x 1.5°3.6° x 0.8°-1.8° vert. resolution31 levels40 levels25 levels mar. biogeochem. PISCES HAMOCC5.1OCMIP-2 mod. CO 2 emissions GtC/yr historicalA2

4. !!! The models were forced by CO 2 -emissions only! *) Consequently, they produce their own patterns of climate variability and can not be compared to observations on a year by year basis. Model evaluation needs to be done statistically and by comparison with climatological distributions. *) NCAR also includes forcing by other GHGs, solar activity and volcanic emissions.

5. Modeled and Observed ΔpCO 2

6. Spatial and Temporal Correlations of ΔpCO 2 Taka 2007

7. Sea-Air CO 2 -flux Equatorial Pacific (165°W-90°W, 5°N-10°S) Feely et al., JGR, 2006LQ2007 data from Le Quéré et al., Science, 2007 observedmodeled

8. Climate Impact on Marine Biological Production R 2 =0.70R 2 =0.67 R 2 =0.02R 2 =0.05 SISST ano 0 0 -0.2-1.0 -0.1-0.5 0.2 1.0 0.1 0.5 SISST ano 0 0 -0.2-1.0 -0.1-0.5 0.2 1.0 0.1 0.5 SI = stratification index ρ 200 – ρ surf (kg m -3 ) R 2 =0.73R 2 =0.85 SISST ano 0 0 -0.2-1.0 -0.1-0.5 0.2 1.0 0.1 0.5 El Nino La Nina SEAWIFS-data from Behrenfeld et al., Nature, 2006

9. R 2 =0.70R 2 =0.67 R 2 =0.02R 2 =0.05 SISST ano 0 0 -0.2-1.0 -0.1-0.5 0.2 1.0 0.1 0.5 SISST ano 0 0 -0.2-1.0 -0.1-0.5 0.2 1.0 0.1 0.5 SI = stratification index = ρ 200 – ρ surf (kg m -3 ) R 2 =0.73R 2 =0.85 SISST ano 0 0 -0.2-1.0 -0.1-0.5 0.2 1.0 0.1 0.5 El Nino La Nina slope=-876 slope=-787 slope=-151 slope=-246 SISST ano 0 0 -0.2-1.0 -0.1-0.5 0.2 1.0 0.1 0.5 R 2 =0.04R 2 =0.03 NCAR Schneider et al., Biogeosciences Discuss., 2007 Climate Impact on Marine Biological Production

10. Temporal Trends 1985-2005 ATMOCE IPSL1.491.26 MPIM1.691.60 NCAR1.881.73 pCO 2 increase (ppm/per year): Anomalies of Surface Ocean pCO 2 Increase (Ocean-Atmosphere), ppm

11. Conclusions All models compare considerably better to the new pCO 2 climatology (Takahashi et al., 2007) than to the one before. The seasonal cycle of surface ocean pCO 2 is well represented by two out of three coupled models yielding a better match with observations than annual mean fields. For all OCMIP-2 models it is the opposite. Coupled model have difficulties in capturing the amplitude and/or frequency of the interannual variability of Air-Sea CO 2 -exchange. In contrast to observations models show a slightly lower surface ocean pCO 2 increase than the atmosphere, suggesting a still increasing oceanic sink for anthropogenic CO 2. (-> ozone effect?) For a realistic representation of the interannual variability of marine productivity next to ocean circulation the iron cycle and nutrient co- limitations are of major importance.

12. Anthropogenic Air-Sea CO 2 -fluxes Inventories of Anthropogenic CO 2 (GtC): 1995 2000 IPSL 103115 MPIM 91112 NCAR 87 98 Sabine 118 (Sabine et al., Science, 2004)

13. Regional Sea-Air CO 2 -fluxes GtC/yr > 44 S44 S - 18 S18 S - 18 N18 N - 49 N> 49 N

14. SST - CO 2 flux relationships

15. SST - CO 2 flux relationships (anomalies)

16. El Nino Variability

17. Background 1.Can we reduce the uncertainty in estimating the oceanic sink for anthropogenic CO 2 ? 2.Is there a significant contribution of marine biological productivity to the air-sea CO 2 -exchange?