Presenter: Jan Rieck (McGill University)

Description:
Mesoscale eddies are ubiquitous features of the global oceans that can be observed in all basins throughout the year. In polar regions however, observations of mesoscale eddies are hindered by the presence of sea ice, which requires additional efforts and specialized equipment for in-situ measurements and limits the air- and space-borne detection of eddies to open water and marginal ice zones. Mesoscale eddies under compact sea ice and their interactions with the ice have nonetheless been observed and simulated, but many of the processes involved in these interactions are not well known. To investigate under which conditions and through which mechanisms mesoscale eddies interact with compact sea ice, this study utilizes the Massachusetts Institute of Technology general circulation model (MITgcm) in an idealized, reentrant channel configuration at eddy-resolving horizontal resolution. The simulation exhibits a stratified surface ocean with fresh, cold water on top of saltier, warmer water, resembling the stratification of many regions in the southern polar ocean. In this setting, anticyclonic and cyclonic eddies are generated in the vicinity of the mean zonal current and propagate near and under sea ice, especially so in winter, when the sea ice extends further equatorward. On average, the anticyclones trap anomalously warm water in their core and transport it towards the sea ice, while the cyclones have anomalously cold water at their core. Additionally, mesoscale eddies enhance the vertical exchange between the deep ocean and the surface layer. The integrated effect of the lateral and vertical processes on sea ice is a reduced (increased) thickness over anticyclones (cyclones). However, depending on the dynamical and hydrographic setting, the inverse can also be observed (i.e. reduced thickness over cyclones and vice versa). The exact mechanisms behind this are to be determined.