Drivers of the Mixed Layer Salinity Variability in the Seasonal Ice Zone of the Arctic Ocean

The Arctic seasonal ice zone experiences complex atmosphere-ocean-ice interactions, including an intensification of the seasonal sea ice freezing and melting fluxes. However, these processes are still not fully elucidated and are generally poorly represented in state-of-the-art climate models. In this study, we focus on the seasonal ice zone, using a regional ocean—sea ice model at high resolution to provide a comprehensive quantification of the mixed layer salinity budget. The seasonal variability of the mixed layer salinity is clearly amplified in the region characterized by a seasonal sea ice, and results largely from the well-known 1D vertical balance between the freshwater flux at the surface arising from sea ice melt and freezing processes, and vertical mixing and entrainment occurring at the base of the mixed layer. Over the Arctic shelves, our results reveal a contrasted dynamics from this 1-D balance, with significant contributions from (a) horizontal advection due to the shallow bathymetry and (b) freshwater from the river discharges. Overall, the largest amplitudes of the mixed layer processes are found within less than 100 km on each side of the sea ice edge. This highlights the need to better observe and understand the ocean-sea ice-atmosphere processes in the seasonal and marginal ice zones.