Dynamics of Convection and Submesoscale Eddy Formation Under Sea Ice Leads

Kaylie Cohanim, Ken Zhao and Andrew Stewart, University of California Los Angeles, Atmospheric and Oceanic Sciences, Los Angeles, United States
Interaction between the atmosphere and the ocean mixed layer in sea ice-covered regions is strongly influenced by leads, which are long, narrow openings between sea ice floes. Refreezing in these leads is associated with brine rejection that has been shown to be critical for maintaining polar halocline stratification. The rejected brine is distributed to the mixed layer and halocline via the formation of buoyant salt plumes beneath the leads. The resulting line plumes typically undergo baroclinic instabilities, confining the salt anomalies to the cores of anticyclonic submesoscale coherent vortices that have the potential to redistribute the anomalies over large horizontal distances. However, it remains unclear how the temperature and salinity stratification influence the strength and depth of the lead-driven buoyancy anomalies in the polar halocline, and thus the size, salinity and longevity of the resulting eddies.

In this study, we investigate these relationships by conducting a suite of idealized numerical simulations in 2D and 3D domains (with and without eddy generation, respectively). As a baseline for our numerical model results, we present dynamical theories that predict the plume convection depth, buoyancy anomaly, and eddy scale as a function of initial stratification and surface buoyancy forcing. Our results suggest that the pycnocline penetration depth is highly dependent on salinity stratification, whereas the eddy properties are most strongly influenced by the lead width. Furthermore, our results reveal that the mechanical feedback of the sea ice on the mixed layer inhibits the migration, and possibly the size and merging of eddies. The sensitivity experiments conducted in this study suggest that the intermittent opening of leads can efficiently populate the polar halocline with submesoscale coherent vortices with diameters of O(10km), and may help better constrain the partitioning between local and nonlocal salinity anomalies due to sea ice leads.