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Surface Ocean pCO 2 and Air-Sea CO 2 -exchange in Coupled Models

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

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Surface Ocean pCO 2 and Air-Sea CO 2 -exchange in Coupled Models

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  1. Surface Ocean pCO2 and Air-Sea CO2-exchange in Coupled Models Birgit Schneider1*,Laurent Bopp1, Patricia Cadule1, Thomas Frölicher2, Marion Gehlen1, Fortunat Joos2, Corinne Le Quéré3 and Joachim Segschneider4 1Laboratoire 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 pCO2 and Air-Sea CO2-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 • 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 CO2 emissions GtC/yr IPSL MPIM NCAR ocean model OPA 8 MPIOM NCAR-CSM1.4 hor. resolution ORCA 2° x 2°x cos lat 1.5° x 1.5° 3.6° x 0.8°-1.8° vert. resolution 31 levels 40 levels 25 levels mar. biogeochem. PISCES HAMOCC5.1 OCMIP-2 mod. All models have been treated according to the C4MIP protocol. (Friedlingstein et al., 2006) Period investigated: 1985-2005 historical A2

  4. !!! The models were forced by CO2-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 ΔpCO2

  6. Spatial and Temporal Correlations of ΔpCO2 Taka 2007 Taka 2007 Taka 2007

  7. Sea-Air CO2-flux Equatorial Pacific(165°W-90°W, 5°N-10°S) observed modeled Feely et al., JGR, 2006 LQ2007 data from Le Quéré et al., Science, 2007

  8. Climate Impact on Marine Biological Production SI SSTano SI SSTano SI SSTano -0.2 -1.0 -0.2 -1.0 -0.2 -1.0 -0.1 -0.5 -0.1 -0.5 -0.1 -0.5 0 0 0 0 0 0 0.1 0.5 0.1 0.5 0.1 0.5 0.2 1.0 0.2 1.0 0.2 1.0 La Nina SI= stratification index ρ200 – ρsurf(kg m-3) R2=0.73 R2=0.85 El Nino SEAWIFS-data from Behrenfeld et al., Nature, 2006 R2=0.02 R2=0.05 R2=0.70 R2=0.67

  9. Climate Impact on Marine Biological Production SI SSTano SI SSTano SI SSTano SI SSTano -0.2 -1.0 -0.2 -1.0 -0.2 -1.0 -0.2 -1.0 -0.1 -0.5 -0.1 -0.5 -0.1 -0.5 -0.1 -0.5 0 0 0 0 0 0 0 0 0.1 0.5 0.1 0.5 0.1 0.5 0.1 0.5 0.2 1.0 0.2 1.0 0.2 1.0 0.2 1.0 La Nina R2=0.73 R2=0.85 R2=0.04 R2=0.03 slope=-876 slope=-151 El Nino R2=0.70 R2=0.67 R2=0.02 R2=0.05 slope=-787 slope=-246 NCAR SI= stratification index = ρ200 – ρsurf(kg m-3) Schneider et al., Biogeosciences Discuss., 2007

  10. Temporal Trends 1985-2005 Anomalies of Surface Ocean pCO2 Increase (Ocean-Atmosphere), ppm pCO2 increase (ppm/per year): ATM OCEIPSL 1.49 1.26MPIM 1.69 1.60NCAR 1.88 1.73

  11. Conclusions • All models compare considerably better to the new pCO2 climatology (Takahashi et al., 2007) than to the one before. • The seasonal cycle of surface ocean pCO2 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 CO2-exchange. • In contrast to observations models show a slightly lower surface ocean pCO2 increase than the atmosphere, suggesting a still increasing oceanic sink for anthropogenic CO2. (-> 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 CO2-fluxes Inventories of Anthropogenic CO2 (GtC): 1995 2000IPSL 103 115MPIM 91 112NCAR 87 98Sabine 118 (Sabine et al., Science, 2004)

  13. Regional Sea-Air CO2-fluxes GtC/yr > 44 S 44 S - 18 S 18 S - 18 N 18 N - 49 N > 49 N

  14. SST - CO2flux relationships

  15. SST - CO2flux relationships (anomalies)

  16. El Nino Variability

  17. Background • Can we reduce the uncertainty in estimating the oceanic sink for anthropogenic CO2? • Is there a significant contribution of marine biological productivity to the air-sea CO2-exchange?

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