A model study of circulation and cross-shelf exchange on the west Antarctic Peninsula continental shelf

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Abstract Exchange of warm, nutrient-rich Circumpolar Deep Water (CDW) onto Antarctic continental shelves and coastal seas has important effects on physical and biological processes in these regions. The present study investigates the locations of this exchange and their dynamics in the west Antarctic Peninsula with a high-resolution three-dimensional numerical model. The model circulation is forced by daily wind stress along with heat and salt fluxes calculated by bulk formulae. All surface fluxes are modified by an imposed climatological ice cover. The model circulation compares favorably to general schematics of the flow based on dynamic topography, water properties from recent hydrography, and ADCP measurements. The sea-surface temperature is similar to satellite estimates except that the model temperatures are slightly higher than observations in the summer and lower in the winter. The seasonal variation of the depth and temperature of the model mixed layer matches observations reasonably well. Sub-pycnocline temperature shows evidence of persistent intrusion of warm CDW onto the shelf, for example, at the shelf break offshore of Adelaide Island. There is a significant correlation between the curvature of the shelf break and the volume transport across the shelf break, indicating that circulation crosses the shelf break in places where the tendency of the flow to maintain a given direction would have it cross a strongly curved bathymetric contour. A momentum term balance shows that momentum advection helps to force flow across the shelf break in specific locations due to the curvature of the bathymetry. For the model to create a strong intrusion of CDW onto the shelf, it appears two mechanisms are necessary. First, CDW is driven onto the shelf at least partially due to momentum advection and the curvature of the shelf break. Then, the general shelf circulation pulls the CDW into the interior.