Wind-driven freshwater export at Cape Farewell

The Atlantic Meridional Overturning Circulation redistributes heat across the Atlantic and is therefore a critical element of the climate system. Increased freshwater fluxes to the subpolar north Atlantic from the Greenland ice sheet and from the Arctic could lead to a strengthening of stratification in deep convection regions, and impact deep water formation and the overturning circulation. However, this additional freshwater first enters the boundary current on the Greenland shelf, and freshwater pathways from the shelf to deep convection regions are still unclear. In this study, we investigate the possible role of winds in driving short-lived freshwater export events from the south-east Greenland shelf to the deep convection region of the Irminger Sea.

Along the south-eastern shelf, strong and consistent north-easterly winds tend to restrain fresh surface waters over the shelf. This wind pattern changes at Cape Farewell, where strong westerly winds could lead to across-shelf export. Using a high-resolution model, we identify strong wind events and investigate their impact on freshwater export. The strongest westerly winds, westerly tip jets, are associated with the strongest and deepest freshwater export across the shelfbreak, with a mean of 40.7 mSv of freshwater in the first 100 m (with reference salinity 34.9). These wind events tilt isohalines and extend the front offshore, especially over Eirik Ridge. Moderate westerly events are associated with weaker export across the shelfbreak (mean of 17 mSv) but overall contribute to more freshwater export throughout the year, including in summer, when the shelf is particularly fresh. Particle tracking shows that half of the surface waters crossing the shelfbreak during tip jet events are exported away from the shelf, either entering the Irminger Gyre, or being driven over Eirik Ridge. During strong westerly wind events, sea-ice detaches from the coast and veers towards the Irminger Sea, but the contribution of sea-ice to freshwater export at the shelfbreak is minimal compared to liquid freshwater export.