Abstract

The circulation of the northwestern Weddell Sea influences the ventilation of deep water in the global overturning circulation as well as the injection of nutrient-rich shelf waters into the Scotia Sea.  The physical processes that govern variability in these different exchange processes are explored using both idealized models of the gyre circulation and observations from ocean glider and drifter deployments.  The Weddell gyre’s complex boundary current system is found to undergo interannual variations in its position and strength that impacts surface export pathways to the Scotia Sea and thus chlorophyll distributions.  A simple two-layer model of the gyre dynamics is able to explain this variability and emphasizes the role of mesoscale motions in rapid adjustments of the boundary currents over the continental slope.  This view differs from traditional wave-induced modification processes.  Hydrographic profiles collected from ocean gliders during a two month survey of this slope-front circulation are also consistent with an important role for mesoscale eddies influencing both export from the Weddell Sea and cross-frontal exchange at the shelf break.  These results suggest that mesoscale variability may, in part, determine the closure of the ocean’s lower overturning cell at its southern boundary.