Preconditioning of the Weddell Sea Polynya by the Ocean Mesoscale and Dense Water Overflows.

Dufour, Carolina O., Morrison, Adele K., Griffies, Stephen M., Frenger, Ivy , Zanowski, Hannah and Winton, Michael (2017) Preconditioning of the Weddell Sea Polynya by the Ocean Mesoscale and Dense Water Overflows. Open Access Journal of Climate, 30 (19). pp. 7719-7737. DOI 10.1175/JCLI-D-16-0586.1.

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The Weddell Sea polynya is a large opening in the open-ocean sea ice cover associated with intense deep convection in the ocean. A necessary condition to form and maintain a polynya is the presence of a strong subsurface heat reservoir. This study investigates the processes that control the stratification and hence the buildup of the subsurface heat reservoir in the Weddell Sea. To do so, a climate model run for 200 years under preindustrial forcing with two eddying resolutions in the ocean (0.25° CM2.5 and 0.10° CM2.6) is investigated. Over the course of the simulation, CM2.6 develops two polynyas in the Weddell Sea, while CM2.5 exhibits quasi-continuous deep convection but no polynyas, exemplifying that deep convection is not a sufficient condition for a polynya to occur. CM2.5 features a weaker subsurface heat reservoir than CM2.6 owing to weak stratification associated with episodes of gravitational instability and enhanced vertical mixing of heat, resulting in an erosion of the reservoir. In contrast, in CM2.6, the water column is more stably stratified, allowing the subsurface heat reservoir to build up. The enhanced stratification in CM2.6 arises from its refined horizontal grid spacing and resolution of topography, which allows, in particular, a better representation of the restratifying effect by transient mesoscale eddies and of the overflows of dense waters along the continental slope.

Document Type: Article
Keywords: Deep convection; Mesoscale processes; Mixing; Topographic effects; Climate models
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BM Biogeochemical Modeling
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1175/JCLI-D-16-0586.1
ISSN: 0894-8755
Date Deposited: 18 Dec 2017 07:05
Last Modified: 06 Feb 2020 09:16

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