Climate feedback on the marine carbon cycle in CarboOcean Earth System Models J. Segschneider 1, E. Maier-Reimer 1 L. Bopp 2, J. Orr 2 1 Max-Planck-Institute for Meteorology, Hamburg, Germany 2 Institut Pierre-Simon Laplace, Gif-sur-Yvette, France EU FP6 IP (GOCE)

Background : Main goal of core theme 5 within CarboOcean: Provide coupled climate carbon cycle simulations to provide predictions of oceanic carbon sources and sinks identify and possibly quantify the feedback processes between climate and the oceanic carbon cycle

Atmospheric pCO 2 rises because of anthropogenic emissions Atmospheric temperature rises and hence circulation is changed Ocean state (temperature and circulation) are influenced by atmospheric conditions, internal dynamics may amplify perturbations Physical conditions impact on marine carbon cycle and hence oceanic CO 2 uptake, which impacts on atmospheric pCO 2 Controlling mechanisms for climate feedback on marine CO 2 cycle

Possible marine feedback mechanisms physical pump: - higher SST/reduced solubility - reduced deep water formation/transport to abyss + less ice cover/increased gas exchange at high latitudes ? wind/gas exchange biological pump: - weakening MOC, less nutrients at surface, less export alkalinity pump: - acidifcation/less calcification + less silicate/more calcification Sign indicates impact on oceanic CO2 uptake

Instrument Earth System Models CM4, COSMOS1 comprising - Atmosphere dynamics and chemistry LSCE: LMDZ-4, MPIM: ECHAM5 - Ocean dynamics and biogeochemistry LSCE: ORCA/PISCES, MPIM: MPIOM/HAMOCC5.1 - Land biosphere LSCE: ORCHIDEE, MPIM: JSBACH To be added: NCAR CSM1.4 (some results, as used by Bern group) BCM (Bergen climate model)

Forcing protocol (same as C4MIP): historical 20C3M CO 2 emissions (418GtC) future SRES A2 CO 2 emissions (1770GtC) two experiments: one with climate feedback one without climate feedback

Quantifying sensitivity: New results from CarboOcean  ocean  ocean IPSL MPI C4MIP

IPSL-CM2CIPSL-CM4MPIMNCAR  o (PgC / °C) Quantifying climate impact

Mechanisms for climate impact: Increasing Sea Surface Temperature decreases CO 2 solubility Decreased mixing with sub-surface and deep- waters prevents the penetration of anthropogenic carbon into deep ocean Decrease in biological production reduces the amount of carbon transported to depth. Identifying mechanisms for climate impact

NCAR IPSL CM2 IPSL CM4 MPIM NCAR  SST [ o C]  Export [PgC/yr] Identifying mechanisms:

NCAR IPSL CM2 IPSL CM4 MPIM NCAR  SST [ o C] Identifying mechanisms: NCAR IPSL CM2 IPSL CM4 MPIM NCAR  mixed layer depth [m]

IPSL CM2 IPSL CM4 MPIM  MOC [Sv] NCAR  SST [ o C] Identifying mechanisms:

NCAR IPSL CM2 IPSL CM4 MPIM NCAR IPSL CM2 IPSL CM4 MPIM  mixed layer depth [m]  MOC [Sv] Identifying mechanisms:

Identifying/Quantifying climate impact: SST Export  

Identifying/Quantifying climate impact: MOC MLD  

Regionalisation

Identifying mechanisms: - 10%

opex % Identifying mechanisms:

caex % Identifying mechanisms:

Conclusions -identifying mechanisms- CO 2 induced warming and weaker MOC weaken physical pump Decrease in export production weakens biological pump Increase in calcite export strengthens alkalinity counter pump All this points to weakening potential for oceanic uptake

Conclusions -quantifying feedback- CarboOcean models range from -16 to -30 GtC/K indication for linear relationship with  : nearest for MLD less clear for export (if CM4 omitted), inverse if anything for MOC (?) scattered for SST

MPI IPSL Sabine et al Anthropogenic DIC

MPI-OM grid