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Southern Ocean Seasonal Restratification Delayed by Submesoscale Wind–Front Interactions

du Plessis, Marcel and Swart, Sebastiaan and Ansorge, Isabelle J. and Mahadevan, Amala and Thompson, Andrew F. (2019) Southern Ocean Seasonal Restratification Delayed by Submesoscale Wind–Front Interactions. Journal of Physical Oceanography, 49 (4). pp. 1035-1053. ISSN 0022-3670. doi:10.1175/jpo-d-18-0136.1.

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Ocean stratification and the vertical extent of the mixed layer influence the rate at which the ocean and atmosphere exchange properties. This process has direct impacts for anthropogenic heat and carbon uptake in the Southern Ocean. Submesoscale instabilities that evolve over space (1–10 km) and time (from hours to days) scales directly influence mixed layer variability and are ubiquitous in the Southern Ocean. Mixed layer eddies contribute to mixed layer restratification, while down-front winds, enhanced by strong synoptic storms, can erode stratification by a cross-frontal Ekman buoyancy flux. This study investigates the role of these submesoscale processes on the subseasonal and interannual variability of the mixed layer stratification using four years of high-resolution glider data in the Southern Ocean. An increase of stratification from winter to summer occurs due to a seasonal warming of the mixed layer. However, we observe transient decreases in stratification lasting from days to weeks, which can arrest the seasonal restratification by up to two months after surface heat flux becomes positive. This leads to interannual differences in the timing of seasonal restratification by up to 36 days. Parameterizing the Ekman buoyancy flux in a one-dimensional mixed layer model reduces the magnitude of stratification compared to when the model is run using heat and freshwater fluxes alone. Importantly, the reduced stratification occurs during the spring restratification period, thereby holding important implications for mixed layer dynamics in climate models as well as physical–biological coupling in the Southern Ocean.

Item Type:Article
Related URLs:
URLURL TypeDescription
Swart, Sebastiaan0000-0002-2251-8826
Thompson, Andrew F.0000-0003-0322-4811
Additional Information:© 2019 American Meteorological Society. Manuscript received 22 June 2018, in final form 11 December 2018. Published online 11 April 2019. MdP acknowledges numerous research visits to the Department of Marine Science, University of Gothenburg, and a visit to Woods Hole Oceanographic Institution, which greatly enhanced this work. We thank SANAP and the captain and crew of the S.A. Agulhas II for their assistance in the deployment and retrieval of the gliders. We acknowledge the work of SAMERC-STS for housing, managing, and piloting the gliders. SS was supported by NRF-SANAP Grant SNA14071475720 and a Wallenberg Academy Fellowship (WAF 2015.0186). Lastly, SS thanks the numerous technical assistance, advice, and IOP hosting provided by Geoff Shilling and Craig Lee of the Applied Physics Laboratory, University of Washington.
Funding AgencyGrant Number
South African National Antarctic ProgramSNA14071475720
National Research Foundation (South Africa)UNSPECIFIED
Wallenberg Academy FellowshipWAF 2015.0186
Subject Keywords:Atmosphere-ocean interaction; Fronts; Oceanic mixed layer; In situ oceanic observations; Interannual variability; Seasonal cycle
Issue or Number:4
Record Number:CaltechAUTHORS:20190529-154338942
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95891
Deposited By: Tony Diaz
Deposited On:29 May 2019 22:49
Last Modified:16 Nov 2021 17:16

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