Tracking Labrador Sea Water property signals along the Deep Western Boundary Current

Abstract

Observations of the Deep Western Boundary Current (DWBC) at Line W on the western North Atlantic continental slope southeast of Cape Cod from 1995 to 2014 reveal water mass changes that are consistent with changes in source water properties upstream in the Labrador Sea. This is most evident in the cold, dense, and deep class of Labrador Sea Water (dLSW) that was created and progressively replenished and deepened by recurring winter convection during the severe winters of 1987–1994. The arrival of this record cold, fresh, and low potential vorticity anomaly at Line W lags its formation in the Labrador Sea by 3–7 years. Complementary observations along the path of the DWBC provide further evidence that this anomaly is advected along the boundary and indicate that stirring between the boundary and the interior intensifies south of the Flemish Cap. Finally, the consistency of the data with realistic advective and mixing time scales is assessed using the Waugh and Hall (2005) model framework. The data are found to be best represented by a mean transit time of 5 years from the Labrador Sea to Line W, with a leading order role for both advection by the DWBC and mixing between the boundary flow and interior waters.