The Impact of Submesoscale Dynamics on Arctic Freshwater Fronts

Marion S Alberty1,2, Sonya Legg3, Robert Hallberg4, Jennifer A MacKinnon5, Janet Sprintall5,6, Matthew H Alford6,7, John Mickett8 and Elizabeth Fine5, (1)Princeton University, Atmospheric and Ocean Sciences, Princeton, NJ, United States, (2)NOAA Geophyscial Fluid Dynamics Laboratory, Princeton, NJ, United States, (3)Princeton University, Princeton, NJ, United States, (4)NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, NJ, United States, (5)Scripps Institution of Oceanography, La Jolla, CA, United States, (6)University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, (7)Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, United States, (8)University of Washington, Applied Physics Laboratory, Seattle, WA, United States
The seasonal melting of sea ice is a source of freshwater in the Arctic which can create a cool, fresh layer, insulating sea ice from the underlying warmer, saltier mixed layer. At the same time, the lateral buoyancy gradients produced by this freshwater flux provide a source of available potential energy which, through submesoscale instability, can enhance lateral and vertical fluxes of salt and heat across the interface between the meltwater layer and the surface mixed layer. We present novel, high-resolution observations of upper ocean dynamics in the Beaufort Gyre from two September cruises. These observations indicate a significant, positive relationship between the strength of submesoscale lateral gradients and turbulent mixing in the upper ocean. Motivated by these results, we initialize numerical simulations using our observations of a sharp, freshwater front and analyze the output to investigate the role of submesoscale dynamics in upper Arctic ocean heat and salt budgets. We compare heat and salt budgets for simulations which resolve both submesoscale and mesoscale dynamics, and coarser resolution simulations which only capture the mesoscale, highlighting the importance of the submesoscale-induced buoyancy flux. We also compare the resolved submesoscale buoyancy fluxes to estimates based on current parameterizations. Finally the relationship between the surface freshwater flux and the strength and persistence of the submesoscale dynamics are investigated for a range of realistic surface forcing.