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The East Greenland Boundary Current System South of Denmark Strait

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Four high-resolution hydrographic sections were occupied across the East Greenland shelf and slope to the south of Denmark Strait near 65°N in the summer seasons of 2001, 2003, 2004 and 2007 respectively, the 2004 section being aboard RRS James Clark Ross. Each section included use of a vessel-mounted acoustic Doppler current profiler, allowing the computation of absolute geostrophic velocities. The boundary current at this location comprises the East Greenland/Irminger Current (EGIC) in the upper layer, the Deep Western Boundary Current (DWBC) at the base of the continental slope, and the East Greenland spill jet, which resides inshore and beneath the EGIC . The bottom-intensified spill jet, first observed only in 2001, was seen in every occupation and in the mean transported 4.8 ± 2.3 Sv equatorward, which is equivalent to the DWBC at this latitude (4.8 ± 1.2 Sv). The spill jet displayed considerable variability from section-to-section, which appeared to be linked to the upper-layer hydrographic front that separates warm and salty Atlantic-origin water in the Irminger Basin from the cold and fresh Arctic-origin water on the shelf. When this EGIC front is located near the shelfbreak (as in 2001/2003), the spill jet is confined to the outer shelf/upper slope and its transport is smaller. During these times there is less mixing and the water advected by the jet is significantly lighter than that transported by the DWBC . In contrast, when the EGIC is located seaward of the shelfbreak (as in 2004/2007) the spill jet extends farther down the continental slope and its volume flux is larger. In these instances there is stronger mixing and the spill jet can transport water as dense as the Denmark Strait Overflow Water. This strong mixing is in part promoted by the strong horizontal potential vorticity gradients around the Spill Jet, which in turn drive a number of instability processes including symmetric instability. Differences in the character of the spill jet between each section may represent different stages in the spilling process by which dense water cascades off the shelf south of Denmark Strait to form the spill jet. These results suggest that the spill jet is a permanent feature of the summertime circulation in this region and contributes significantly to the intermediate, and at times deep, limb of the Atlantic Meridional Overturning Circulation.

This talk is part of the British Antarctic Survey - Polar Oceans seminar series series.

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