Abstract
The circulation and water mass transports north of the Denmark Strait are investigated using recently collected and historical in situ data along with an idealized numerical model and atmospheric reanalysis fields. Emphasis is placed on the pathways of dense water feeding the Denmark Strait Overflow Water plume as well as the upper-layer circulation of freshwater. It is found that the East Greenland Current (EGC) bifurcates at the northern end of the Blosseville Basin, some 450km upstream of the Denmark Strait, advecting overflow water and surface freshwater away from the boundary. This “separated EGC” flows southward adjacent to the previously identified North Icelandic Jet, indicating that approximately 70% of the Denmark Strait Overflow Water approaches the sill along the Iceland continental slope. Roughly a quarter of the freshwater transport of the EGC is diverted offshore via the bifurcation. Two hypotheses are examined to explain the existence of the separated EGC. The atmospheric fields demonstrate that flow distortion due to the orography of Greenland imparts significant vorticity into the ocean in this region. The negative wind stress curl, together with the closed bathymetric contours of the Blosseville Basin, is conducive for spinning up an anti-cyclonic gyre whose offshore branch could represent the separated EGC. An idealized numerical simulation suggests instead that the current is primarily eddy-forced. In particular, baroclinic instability of the model EGC spawns large anti-cyclones that migrate offshore and coalesce upon reaching the Iceland continental slope, resulting in the separated EGC. Regardless of the formation mechanism, the recently obtained shipboard data and historical hydrography both indicate that the separated EGC is a permanent feature of the circulation north of the Denmark Strait.
Highlights
The meridional exchange across the Greenland-Scotland Ridge is of key importance for the 3 North Atlantic climate system
Our results show that the separated East Greenland Current (EGC) provides a means for transporting freshwater as well 594 as overflow water from the western boundary into the interior of the Blosseville Basin
While the Jan Mayen Current is to some extent topographically steered by the Jan Mayen Fracture Zone (Bourke et al, 1992), Figure 2 shows no corresponding bathymetric feature farther south that would cause the East Icelandic Current to diverge from the EGC
Summary
The meridional exchange across the Greenland-Scotland Ridge is of key importance for the 3 North Atlantic climate system. As part of 7 the horizontal circulation, fresh surface waters from the Arctic Ocean are fluxed southward along 8 the western boundary of the Nordic seas and across the ridge Most of this freshwater, as well as 9 the densest portion of the AMOC – the Denmark Strait Overflow Water (DSOW) – pass between Greenland and Iceland. We provide evidence of a heretofore unknown interior branch of the EGC north of the Denmark Strait that impacts the supply of both buoyant freshwater and dense overflow water to the strait. We refer to this current as the “separated EGC”.
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