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Stirring of sea ice meltwater enhances submesoscale fronts in the Southern Ocean

Giddy, I. and Swart, S. and Thompson, A. F. and du Plessis, M. and Nicholson, S. A. (2020) Stirring of sea ice meltwater enhances submesoscale fronts in the Southern Ocean. . (Unpublished)

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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.

Item Type:Report or Paper (Discussion Paper)
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ftp://ssh.roammiz.comRelated ItemData - giddy 2020 ItemCode
Giddy, I.0000-0002-8926-3311
Swart, S.0000-0002-2251-8826
Thompson, A. F.0000-0003-0322-4811
du Plessis, M.0000-0003-2759-2467
Nicholson, S. A.0000-0002-1226-1828
Additional Information:Published Online: Thu, 24 Sep 2020. This work was supported by the following grants of SS: Wallenberg Academy Fellowship (WAF 2015.0186), Swedish Research Council (VR 2019-04400), STINT-NRF Mobility Grant. SN and SS: NRF-SANAP (SNA170522231782) and SN, the Young Researchers Establishment Fund (YREF 2019 0000007361). SS and MdP have received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 821001 (SO-CHIC). AFT is supported by ONR (N00014-19-1-2421), NSF (1829969) and a Linde Center Discovery Fund grant. We thank Sea Technology Services (STS), SANAP, the captain and crew of the S.A. Agulhas II for their field-work/ technical assistance. Zach Erickson, Mar Flexas, and Giuliana Viglione (Caltech) contributed to glider piloting throughout the deployment. S.S. is grateful to Geoff Shilling and Craig Lee (APL, University of Washington) for hosting gliders on IOP. B. Queste is thanked for insightful discussions on glider processing and thermal lag corrections, which was made possible through the UCT-UEA Newton Fund. Special thanks is extended to Isabelle Ansorge for the generous support of I. Giddy in her doctoral studies and training, from which this paper is derived (SANAP 110733 SAMOC-SA). I. Giddy is further supported by the Oppenheimer Memorial Trust. ERA5 data are generated using Copernicus Climate Change Service Information, available online ( All the data used for this analysis can be accessed online ( via anonymous login and navigate to giddy 2020. The code used to produce this analysis is available at
Funding AgencyGrant Number
Knut and Alice Wallenberg FoundationWAF 2015.0186
Swedish Research Council2019-04400
National Research FoundationSNA170522231782
Council for Scientific and Industrial Research (South Africa)2019 0000007361
European Research Council (ERC)821001
Office of Naval Research (ONR)N00014-19-1-2421
Ronald And Maxine Linde Center for Global Environmental ScienceUNSPECIFIED
South African National Antarctic Programme (SANAP)SANAP 110733 SAMOC-SA
Oppenheimer Memorial TrustUNSPECIFIED
Record Number:CaltechAUTHORS:20201023-141150937
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106266
Deposited By: Tony Diaz
Deposited On:23 Oct 2020 21:44
Last Modified:23 Oct 2020 21:44

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