Very high resolution simulation of the Storfjorden polynya in Svalbard

Polynyas are relatively small open-water areas surrounded by sea ice. Their role for climate is considerable since they are a major source of the World Ocean dense water. In winter, very large heat loss occurs in polynyas, resulting in intense sea ice formation. Subsequent brine rejection and shelf convection lead to dense water sinking toward deep ocean basins. In Arctic, sea ice also delays ice melting as part of the dense water feeds a cold halocline which isolates sea ice from the warm subsurface Atlantic Water. However the processes controlling the extension of polynyas are still poorly known due to the difficulty to monitor these regions in winter and to the complexity of the physical processes at stake. Formation and maintenance of polynyas depend on both ice divergence and ocean heat flux, but the role of high frequency dynamics such as tides is still unclear. Inertia gravity wave breaking and induced turbulent mixing can condition sea ice and the fate of newly formed dense water. The goal of this study is to progress in understanding these processes by setting up an ice-ocean simulation of an Arctic coastal polynya. We choose the Storjforden polynya in Svalbard because the region has been relatively well monitored, and received recent attention with the installation of a mooring line in the Storjforden in 2011 (French OPTIMISM project). Simulation is based on the most recent ice and ocean models – NEMO version 3.6 (dynamics and sea ice) –, and configuration (SPITZ) has very high spatio-temporal resolution O(2km) which allows the explicit addition of tides. Spatial coverage is ~500 km x 500 km. It ran long enough (10 years) to retrieve interannual variability. Particular focus is made on the dynamics of the polynya and the characteristics of the dense water formed.