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Submesoscale fronts in the Antarctic Marginal Ice Zone and their responses to wind

High-resolution (0.2- to 120-km) in situ observations were carried out in the Marginal Ice Zone (MIZ) in Southern Ocean from an autonomous surface vehicle paired with a profiling Seaglider during the Austral summer, following sea ice retreat. They show that submesoscale fronts originated after sea ice melt persist into late summer, but their intensity responds rapidly to intermittent wind forcing. Such atmosphere-ocean interactions are expected to be ubiquitous in both the Southern Ocean and Arctic MIZs.

ESA Sentinel‐1 synthetic aperture radar image from 13 November 2018 (1 month prior to robotic deployments) suggesting ocean submesoscale features present at the sea‐ice margins of O(5–10 km) (From Swart et al., 2020).

Southern Ocean air-sea-ice fluxes impact the ocean heat and carbon budget, water mass transformation, the global overturning circulation, sea-ice distribution, and numerous biogeochemical processes. Despite this, atmosphere-ocean physical processes within the Marginal Ice Zone (MIZ) are poorly understood due to the paucity of in situ observations brought about by its seasonal ice cap and remoteness. Satellite radar imagery shows evidence of 1–10 km eddies and jets in the ocean adjacent to the sea‐ice edge around Antarctica.

Using field observations of temperature, salinity, and wind speed from autonomous robotic platforms deployed in the sea‐ice zone for >3 months, the paper Submesoscale fronts in the Antarctic Marginal Ice Zone and Their Response to Wind Forcing provides estimates of the surface ocean density fronts which are controlled primarily by lateral variations in salinity. Results show that during high  wind speeds, these surface fronts temporarily dissipate, indicating an atmosphere‐ocean coupling occurring at the submesoscale. The fronts strengthen again during low wind speed, which is thought to be because the stirring of the fresher surface layer by mesoscale eddies leads to the generation of the submesoscale fronts.

Providing in situ observations of such features improves the understanding of the small‐scale ocean and climate processes at play, such as how heat and carbon may exchange between the atmosphere and the ocean. These atmosphere-ocean interactions are expected to be ubiquitous in both the Southern Ocean and Arctic MIZs.

The work was financially supported by grants from Wallenberg Academy Fellowship (WAF 2015.0186), Swedish Research Council (VR 2019-04400), STINT-NRF Mobility Grant and NRF-SANAP (SNA170522231782), the Terrestrial Hazard Observations and Reporting (THOR) and ONR (N00014-19-1-2421).

FOR MORE INFORMATION

Sebastiaan Swart, Marcel D. du Plessis, Andrew F. Thompson, Louise C. Biddle, Isabelle Giddy, Torsten Linders, Martin Mohrmann, Sarah-Anne Nicholson (2020). Submesoscale fronts in the Antarctic Marginal Ice Zone and Their Response to Wind Forcing Geophysical Research Letter https://doi.org/10.1029/2019GL086649