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Appel à projets générique 2016 projet SOBUMS

SOBUMS : Southern Ocean Biogeochemistry Under Multiple Stressors

The Southern Ocean (region south of 30°S) plays a key role in global biogeochemical cycles. Vertical exchange in the Southern Ocean is responsible for half of the ocean's uptake of anthropogenic CO₂ and for supplying nutrients that fertilize 3/4 of the global ocean's biological production. Both of those services are tied to the Southern Ocean's variability of water mass transport and primary production. While upwelling of deep waters in the Southern Ocean returns carbon and nutrients to the surface, downwelling transports heat, carbon, nutrients and other properties into the ocean interior. The balance between upwelling and release of CO₂ versus carbon uptake into the ocean interior determines the strength of the Southern Ocean sink of CO₂.

Yet there are large changes are occurring in the Southern Ocean's physical and biogeochemical properties. These changes reflect widespread physical changes over the Southern Ocean, including changes in surface winds, solar radiation, sea-ice cover and glacial melt from Antarctica. How the Southern Ocean's primary production and carbon cycle will respond to these changing climate stressors is a matter of concern in the climate science community. An improved understanding of how these changes will affect Southern Ocean biogeochemistry will come from new observing networks and more realistic models, including the ocean biogeocheical components of CMIP6 Earth System Models (ESMs) .

In this perspective, we here intend to study the integrated response of Southern Ocean biogeochemistry to multiple changing stressors and the ability of ocean component of CMIP6 ESMs to capture this response. We will particularly focus on the role of small scale oceanic processes and on the impact of the change in melt and glacial sources of freshwater and iron on Southern Ocean productivity and carbon cycle. The project will also quantify the impact of the sources of uncertainty due to oceanic scale interactions in the CMIP6 ESMs projection.

To this purpose, our 4-years project will use a strategy based on a hierarchy of model studies with various levels of complexity and grid resolution, all based on the community model NEMO-PISCES. We will in particular use an unprecedented series of ensemble simulations of a global « eddying » ocean carbon cycle model. The set-up and the analysis of the model simulations will be coordinated with observations teams and on-going observation programs. Our project team is a unique consortium of physical oceanographers, biogeochemists and climate scientists coming from leading climate research and operational institutions.