Response of submesoscale fronts to storms in the Antarctic marginal ice zone

Sebastiaan Swart1, Marcel du Plessis2, Louise C Biddle3, Sarah-Anne Nicholson4, Andrew F Thompson5, Isabelle S Giddy6,7, Martin Mohrmann8 and Torsten Linders8, (1)University of Gothenburg, Department of Marine Sciences, Gothenburg, Sweden, (2)University of Cape Town, Department of Oceanography, Cape Town, South Africa, (3)University of Gothenburg, Department of Marine Science, Gothenburg, Sweden, (4)Council for Scientific and Industrial Research, Cape Town, South Africa, (5)California Institute of Technology, Pasadena, United States, (6)University of Gothenburg, Gothenburg, Sweden, (7)University of Cape Town, Oceanography, Cape Town, South Africa, (8)University of Gothenburg, Marine Sciences, Gothenburg, Sweden
Abstract:
Surface ocean processes in the sea ice impacted oceans are of key importance to global climate processes, including air-sea-ice fluxes of heat and carbon and sea ice distribution. Submesoscale flows of the upper ocean are energetic motions of O(1km) that are core to setting the surface layer stratification and property distribution in the vertical and horizontal extent of the ocean. Their presence, variability and how they interact with surface forcing, such as winds, are largely unknown in the Southern Ocean, particularly in the sea ice impacted regions. We present the first known submesoscale resolving observations in the Antarctic marginal ice zone (MIZ) using combined autonomous surface vehicles and underwater gliders deployed just 4 days after the spring sea ice melt. The ultra high-resolution dataset reveals a detailed view of haline-dominated lateral density fronts at sub-kilometer scales that persist over the multi-month experiment. Furthermore, storm-driven winds are shown to modify the magnitude and frequency of the lateral submesoscale fronts, emphasising the strongly coupled atmosphere-ocean processes at play. We posture that these wind-front interactions occurring at the submesoscale are caused by a continuous interplay between front slumping and vertical mixing, which arrests lateral shear currents, and referred to as thermohaline shear dispersion. We expect such processes to be ubiquitous in the Southern Ocean MIZ. These findings have implications for accurately determining air-sea-ice flux variability, which current global climate models are sensitive to in the Southern Ocean (IPCC AR5), thereby emphasizing the need to represent these processes correctly, through parameterisations or otherwise.