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

• Published in: Journal of Climate
• Main Authors: Dufour, Carolina O., Morrison, Adele, Griffies, S. M., Frenger, Ivy, Zanowski, Hannah, Winton, Micheal
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Meteorological Society
• Subjects: Weddell Sea; Weddell; Morrison; Sea ice
• Online Access: http://hdl.handle.net/1885/247340; https://doi.org/10.1175/JCLI-D-16-0586.1; https://openresearch-repository.anu.edu.au/bitstream/1885/247340/3/01_Dufour_Preconditioning_of_the_Weddell_2017.pdf.jpg

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. C. O. Dufour was supported by the National Aeronautics and Space Administration (NASA) under Award NNX14AL40G and by the Princeton Environmental Institute (PEI) Grand Challenge initiative. A. K. Morrison was supported by the U.S. Department of Energy under Award DE-SC0012457, by the PEI Grand Challenge initiative, and by the Australian Research Council DECRA Fellowship DE170100184. I. Frenger was supported by the Swiss National Science Foundation Early Postdoc Mobility Fellowship P2EZP2-152133 and NASA under Award NNX14AL40G.