Presenter: William Johns (University of Miami)

Description:
The Iceland Basin contains key circulation components of the upper and deep limbs of the Atlantic Meridional Overturning Circulation (AMOC) in the subpolar North Atlantic Ocean.  Along the eastern side of the basin, the North Atlantic Current (NAC) flows northward within the upper limb of the AMOC, while along the western side of the basin the East Reykjanes Ridge Current (ERRC) and Iceland-Scotland Overflow plume flow southward in the upper and deep ocean, respectively. Both of these currents effectively act as western boundary currents trapped against the steep topography of the Reykjanes Ridge. In this presentation we review the findings from the first six years (2014-2020) of the Overturning in the Subpolar North Atlantic Program on the transports and pathways of these two components of the Iceland Basin's western boundary current system.  The ERRC forms along the northern rim of the Iceland Basin where surface waters from the NAC join with deeper Icelandic Slope Waters along the Iceland-Faroes Ridge to produce a nearly barotropic current with a mean transport of 11-12 Sv. Most of the ERRC turns westward into the Irminger Basin between 56-59°N where the height of the Reykjanes Ridge crest decreases sufficiently to free it from the strong topographic constraint of the ridge.  The Iceland-Scotland Overflow plume forms from Nordic Seas dense waters spilling across the Iceland-Scotland Ridge that entrain a nearly 50/50 mix of NAC thermocline water and mid-depth Labrador Sea water to approximately double its transport to 5-6 Sv (from the original ~3 Sv of dense overflow waters). This transport is significantly larger than most previous estimates and suggests that a substantial fraction of the Iceland-Scotland Overflow water exported from the Iceland Basin must flow southward in the eastern basin of the Atlantic, rather than passing through gaps in the Mid-Atlantic Ridge to join the deep western boundary current system of the western subpolar gyre.