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Stirring of sea ice meltwater enhances submesoscale fronts in the Southern Ocean
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  • Isabelle S. Giddy,
  • Sebastiaan Swart,
  • Andrew F. Thompson,
  • Marcel du Plessis,
  • Sarah-Anne Nicholson
Isabelle S. Giddy
University of Cape Town

Corresponding Author:isgiddy@gmail.com

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Sebastiaan Swart
University of Gothenburg
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Andrew F. Thompson
California Institute of Technology
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Marcel du Plessis
University of Cape Town
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Sarah-Anne Nicholson
Council for Scientific and Industrial Research
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In the sea ice-impacted Southern Ocean, the spring melt of sea ice modifies the upper ocean. These modified waters subduct and enter the global overturning circulation. Submesoscale processes act to modulate the stratification of the mixed layer and therefore mixed layer properties. Sparse observations mean that the role of submesoscales in exchange across the base of the mixed layer in this region is not well constrained. The goal of this study is to determine the interplay between sea ice melt, surface boundary layer forcing, and submesoscale flows in regulating the mixed layer structure in the Antarctic Marginal Ice Zone. High-resolution observations suggest that fine-scale lateral fronts, representative of submesoscale mixed layer eddies (MLEs), arise from mesoscale gradients produced by northwards advecting sea ice meltwater. The strong salinity-driven stratification at the base of the mixed layer confined the MLEs to the upper ocean, limiting submesoscale vertical fluxes across the mixed layer base. This strong stratification prevents the local subduction by submesoscale flow of these modified waters, suggesting that the subduction site that links to the global overturning circulation does not correspond with the location of sea ice melt. However, the presence of MLEs enhanced the magnitude of lateral gradients through stirring and increased the potential for Ekman-driven cross-frontal flow to modulate the stability of the mixed layer and mixed layer properties. The inclusion, particularly of submesoscale Ekman Buoyancy Flux parameterizations, in coupled-climate models, may improve the representation of mixed layer heat and freshwater transport in the ice-impacted Southern Ocean during summer.
Apr 2021Published in Journal of Geophysical Research: Oceans volume 126 issue 4. 10.1029/2020JC016814