1. WP6: Model-based flux assessment CarboOcean final meeting, Os, Norway, 5-9 October 2009 Funding: EU (GOSAC, NOCES), NASA, DOE, Swiss NSF, CSIRO PIs R. Schlitzer, J. Schneider (AWI) A. Oschlies, T. Friedrich (LIMK) C. Moulin, J. Orr (LSCE) I. Totterdell (UK Met. Office) Objectives: Improve interpolation of surface-ocean pCO 2 (seasonal maps of N. Atlantic) Initiate data assimilation activities to better quantify air-sea CO 2 flux Improve prognostic ocean models to assess key gaps

2. State of the art in 2005 First signs of trouble in North Atlantic: Lefevre et al. (2004) A decrease in the sink for atmospheric CO 2 in the North Atlantic, GRL. Lefevre et al. (2005) A comparison of multiple linear regression and neural network techniques for mapping in situ pCO 2 data, Tellus B. Rare efforts to assimilate data to improve CO 2 fluxes (Schlitzer, AWI: annual mean assessment) Coarse-resolution global ocean BGC models Higher-resolution regional ocean BGC models (short simulations)

3. Objectives Improve interpolation of surface-ocean pCO 2 (seasonal maps of North Atlantic): IfM-GEOMAR, LSCE Initiate data assimilation activities to better quantify air-sea CO 2 flux: AWI, LSCE, Met. Office Improve prognostic ocean models to assess some glaring limitations: LSCE

4. Pre-Industrial Sea-to-Air CO 2 Fluxes Reiner Schlitzer, Alfred Wegener Institute for Polar and Marine Research Use CFC and 14 C calibrated global model Assimilate carbon data from ocean interior Data with significant C ant not used!

5. Outgasing in tropics (especially Pacific) Net outgasing around Antarctica Uptake in subtropical and subpolar areas (especially Southern Ocean and North Pacific; North Atlantic sink relatively small) near-zero interhemispheric oceanic C transport (+0.14 PgC/yr) Comparison with other work: 10 – 50% difference larger sink in south Pacific and Indian Mikaloff Fletcher, 2007

6. Assimilate time-dependent C data to find monthly gas-exchange rates that explain the data (AWI, Schlitzer & Schneider) Optimization test case: Good general agreement at BATS Good general agreement at BATS Overall RMS = 20  mol/kg Overall RMS = 20  mol/kg Takahashi, 1999 Model Zonally integrated sea-to-air CO 2 flux CO 2 Fluxes: Initialize with Takahashi (1999) fluxesInitialize with Takahashi (1999) fluxes Modify to achieve agreement with dataModify to achieve agreement with data N. Atlantic POC export much too low in North Atlantic) lead to unrealistically large summer outgasing. C draw-down is realized by outgasing, when much of it in reality is caused by POC export.N. Atlantic POC export much too low in North Atlantic) lead to unrealistically large summer outgasing. C draw-down is realized by outgasing, when much of it in reality is caused by POC export. !! Need to better constrain POC export !!

7. Assimilate ocean pCO 2 data to improve basin-scale, air-sea CO 2 flux estimates (UK Met. Office)  New assimilation scheme developed CARINA data used for assimilation Assimilation scheme See Poster – Totterdell et al.  First tests encouraging RMS reduced near densely spaced obs. Error reduction (July) pCO 2 : assim. – control

8. Participants: C. Moulin, A.-S. Krémeur, A. El Moussaoui, C. Ethé, L. Bopp, E. Dombrowski, E. Greiner, O. Aumont, P. Brasseur Annual-mean chlorophyll Effect of physical data assimilation on simulated Chl a (LSCE) ¼° with assimilation ¼° no assimilation2° no assimilation SeaWIFS Improvements: Southern Ocean Subtropical Gyres *using French MERCATOR modeling framework

9. Effect of physical data assimilation on simulated Chl a Improvements: Reduced Chl a Gulf Stream E-W distribution Ongoing analysis: pCO 2 air-sea CO2 flux carbon-related tracers Problems: Gyre - Chl a too low Labrodor Sea Coastal regions … SeaWIFS Annual-mean chlorophyll ¼° with assimilation ¼° no assimilation2° no assimilation

10. 10 Implemented BGC model (1-D PISCES) with assimilation software (YAO): [LSCE: A. Kane, C. Moulin] - Identified key parameters through sensitivity tests, definition of error matrices, validation using twin experiments,… - Optimized 6 parameters at 1 station. - Optimized 45 parameters at 5 stations and validation through a comparison between a 3D simulation and satellite data.

11. Optimized 45 parameters (surface Chl) - Variables Chl, NO3, POC, Si used at 5 JGOFS stations - Improvements, butr 5 stations remain inadequate - Assimilation of satellite-derived Chl a in progress

12. State of the art in 2005 First signs of trouble in North Atlantic: Lefevre et al. (2004) A decrease in the sink for atmospheric CO 2 in the North Atlantic, GRL. Lefevre et al. (2005) A comparison of multiple linear regression and neural network techniques for mapping in situ pCO 2 data, Tellus B. Rare efforts to assimilate data to improve CO 2 fluxes (Schlitzer, AWI: annual mean assessment) Coarse-resolution global ocean BGC models Higher-resolution regional ocean BGC models (short simulations)

13. WP6 Publications: Friedrich, T., and A. Oschlies (2009), Neural-network based estimates of North Atlantic surface pCO2 from satellite data - a methodological study, J. Geophys. Res., 114, C03020, doi:10.1029/2007JC004646. Friedrich, T., and A. Oschlies (2009), A neural-net based method for estimating North Atlantic surface pCO2 from ARGO float data, J. Geophys. Res., in press. Kane, A., C. Moulin, S. Thiria, L. Bopp, M. Berranda, A. Tagliabue, M. Crépon, F. Badran, O. Aumont, Improving the parameters of a global ocean biogeochemical model by using variational assimilation of in situ data a five JGOFS stations, in prep., 2009. Lachkar, Z., J. C. Orr, J.-C. Dutay, P. Delecluse. On the role of mesoscale eddies in the ventilation of Antarctic Intermediate Water, Deep-Sea Research I, 56, 909-925, 2009. Lachkar, Z., J. C. Orr, and J.-C. Dutay. Seasonal and mesoscale variability of oceanic transport of anthropogenic CO2, Biogeosciences Discuss., 6, 4233-4277, 2009. Lachkar, Z., J. C. Orr, J.-C. Dutay, and P. Delecluse. Effects of mesoscale eddies on global distributions of CFC-11, CO2, and Δ14C, Ocean Science, 3, 461-482, 2007. Raynaud, S., J. C. Orr, O. Aumont, K. Rodgers, and P. Yiou. Interannual-to-decadal variability of North Atlantic air-sea CO2 fluxes, Ocean Science, 2, 43—60, 2006. Schlitzer, R., 2007: Assimilation of radiocarbon and chlorofluorocarbon data to constrain deep and bottom water transports in the world ocean. Journal of Physical Oceanography, 37, 259–276. Telszewski, M., Chazottes, A., Schuster, U., Watson, A. J., Moulin, C., Bakker, D. C. E., González-Dávila, M., Johannessen, T., Körtzinger, A., Lüger, H., Olsen, A., Omar, A., Padin, X. A., Ríos, A. F., Steinhoff, T., Santana-Casiano, M., Wallace, D. W. R., and Wanninkhof, R.: Estimating the monthly pCO2 distribution in the North Atlantic using a self-organizing neural network, Biogeosciences, 6, 1405-1421, 2009.

15. Assimilate ocean pCO 2 data to improve basin-scale, air-sea CO 2 flux estimates (Met. Office)  New assimilation scheme developed CARINA data used for assimilation Assimilation scheme See Poster – Totterdell et al.  First tests encouraging RMS reduced near densely spaced obs. Error reduction (July) pCO 2 : assim. – control

16. Monthly Sea-to-Air CO 2 Fluxes R. Schlitzer & J. Schneider, Alfred Wegener Institute for Polar and Marine Research Objective: Assimilate time-dependent C data and find monthly CO 2 gas exchange rates that explain the data. Optimization works: Good agreement at BATS StationGood agreement at BATS Station Overall rms=20  mol/kgOverall rms=20  mol/kg CO 2 Fluxes: Initialized with Takahashi, 99 fluxesInitialized with Takahashi, 99 fluxes Modified by the model to achieve agreement with dataModified by the model to achieve agreement with data Shortcomings in the model POC export (much too low in North Atlantic) lead to unrealistically large summer outgasing. C draw-down is realized by outgasing, when much of it in reality is caused by POC export.Shortcomings in the model POC export (much too low in North Atlantic) lead to unrealistically large summer outgasing. C draw-down is realized by outgasing, when much of it in reality is caused by POC export. !! Need to better constrain POC export !! Takahashi, 1999 Model Zonally integrated CO2 gas exchange fluxes

17. 1870-2001 2002 - 2007Run 44 years 3 yearsSpin up ERA40 MERCATOR- Vert Forcings online offlineCoupling 2 °1/2 ° 1° forced by 1/4 ° degraded physics Resolutions ORCA2 (P2)‏ ORCA05 (P05)‏ Green- MERCATOR (MV025)‏ Configurations IDRIS (Orsay)‏ Earth Simulator (Japan)‏ MERCATOR (Toulouse)‏ Running center Summary of the different configurations

18. Plans for Plans for OceanCarbon2010 Extend and apply the global adjoint model for quantification of monthly CO 2 air-sea fluxes, POC exports, and 3D carbon transports. Additionally assimilate monthly nutrient (WOA05) and satellite chlorophyll (SeaWiFS, MODIS) data to better constrain model POC exports. Additionally assimilate the new CARINA and SOCAT datasets.

19. Simulated interannual variability (from LSCE)  4 th year progress on sensitivity to 3 factors : 1.Effect of model resolution ? –Mercator-vert collaboration ORCA/PISCES model simulations (2º, ½ º, & ¼º) completed Mercator ocean reanalysis fields: 2001 to 2005 completed –DRAKKAR collaboration Global: Forced NEMO (OPA9) global ocean-model dynamic simulations (2º, ½ º, & ¼º) over last 50 years completed (started - coupling with BGC model) Southern Ocean, high-res (1/12º) regional simulations with NEMO/PISCES in preparation (started - thesis study of Carolina Dufour)  Does explictly resolving eddies change estimated ongoing slowdown in Southern-Ocean CO 2 uptake? 2.Effect of forcing fields ?  NEMO/PISCES simulations over last ~50 years Coding and tests underway (started, Jennifer Simeon) at 3 resolutions (2º, ½ º, & ¼º) & different sets of forcing fields with different sets of forcing fields (NCEP, ERA40, CORE, DFS3, DFS4) Effect of physical data assimilation (SST, altimetry, …)? –Ongoing study within the Mercator-vert project (Moulin et al., 2008)

20. Conclusions: Arctic surface [CO 3 2- ]: high in summer, low in winter (as elsewhere: Bering Sea, Norwegian Sea, Southern Ocean) High summertime [CO 3 2- ] from Biologically driven increase (from DIC drawdown) overwhelms Physically driven decrease (freshening, i.e., dilution) Opposite trend in models with excessive fresh-water input Chukchi Sea surface water: –observed seasonal amplitude (≥12 μmol kg -1 ) (equivalent to past 30+ years of transient change) –That annual cycle + Beringia 2005 summer data, yields Wintertime Ωa < 1 already by 1990 (pCO 2 atm = 354 ppmv), i.e., 30 years sooner than summertime observations