The North Atlantic Deep Western Boundary Current constitutes the lower limb of the Atlantic meridional overturning circulation (MOC), and, as such, is a crucial component of the Earth's climate system. Warm subtropical-origin waters flow northward across the Greenland-Scotland Ridge where they are subject to intense air-sea interaction. After releasing heat to the atmosphere, the resulting dense water returns southward by flowing through the gaps in the ridge and descending the continental slope as overfl ow plumes. These overflows represent the headwaters of the MOC; the largest of these is the Denmark Strait Overflow Water (DSOW) plume which passes southward between Greenland and Iceland and contributes to the DWBC. For many decades oceanographers have b een trying to sort out the origin of the DSOW, and the present paradigm is that the primary source of the overflow water is the East Greenland Current, a southward-flowing current along the continental slope of Greenland. Recently, however, direct shipboa rd velocity measurements north of the Denmark Strait, together with detailed hydrographic information, suggest instead that a substantial fraction of the overflow water originates from the Iceland side of the Denmark Strait, in addition to the Greenland s ide. In order for us to understand how global warming and the consequent enhanced surface freshwater and reduced heat fluxes will impact the MOC, it is imperative that we understand precisely where the DSOW emanates from.
The project proposed here will use data from two high-resolution hydrographic/vessel-mounted ADCP surveys as well as historical hydrographic data to establish the pathway of dense water along the Icelandic slope, quantify its transport, investigate its origin, and examine its importanc e as a supplier of DSOW. This project will contribute both to remedy a gap in our basic understanding of a central part of the MOC system and to clarify how a changing climate will impact the MOC.