Collaborative Research: Mechanisms of Freshwater Exchange Across the East Greenland Shelf

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Freshwater flowing out of the Arctic and from Greenland ice melt has the potential to modulate or even shut down deep convection in the sub-polar North Atlantic. The processes that control this exchange, and how they depend on external factors such as wind and outflow from the Arctic, are not well known and are not well resolved in basin-scale and climate models. Better understanding of the freshwater budget on the shelf, and how these waters get into the deep ocean interior, is essential to improve climate models and understand how the ocean will respond to a changing climate. The dynamically-based diagnostics planned in this project using a hierarchy of numerical ocean circulation models will also inform on mechanisms, locations, and times of exchange in other sensitive areas, such as the east coast of Labrador. Findings from the project will be used in undergraduate and graduate classes. Undergraduate students supported by the Woods Hole Oceanographic Institution Summer Student Fellowship program and assisted by graduate students will gain research experience. Material from the project will also be used in a textbook on ocean circulation. A graduate student will be trained in physical oceanography, geophysical fluid dynamics, and ocean modeling at Johns Hopkins University. The exchange of freshwater between the east Greenland shelf and the interior of the sub-polar North Atlantic and Nordic Seas is a key element in the maintenance and variability of the Atlantic Meridional Overturning Circulation (AMOC) and its sensitivity to changes in atmospheric forcing and freshwater outflow from the Arctic Ocean. A realistic, very high resolution, regional model of the east Greenland shelf and adjacent deep ocean will be combined with idealized, process oriented models and in-situ observations to identify the strength, mechanisms, and sensitivity of this exchange. Processes likely important for this cross-shelf exchange include: surface and bottom Ekman layers; nonlinear eddy fluxes; local and remote wind-forcing; and wind-driven sea ice. The exchange will be diagnosed in a series of realistic model runs. Experiments will be designed with the idealized model to isolate the relevant processes for further study and understanding, and comparisons will be made with in-situ mooring and hydrographic observations and remotely sensed sea ice data. The main goal of the project is to reach a basic understanding of what controls the flux of freshwater from the shelf to the basin interior and how it depends on external forcing (wind, outflow from the Arctic, Greenland runoff) and environmental conditions such as bottom bathymetry and the ambient stratification.