Mean Structure and Interannual Variability of the Slopewater System South of Newfoundland

Abstract

Two sets of repeat hydrographic sections, centered at 55°W and 50°W, are used to study the mean features and long-term variability of the slopewater system south of Newfoundland, inshore of the Gulf Stream. The upper-layer flow is considered first, consisting of the westward-flowing Labrador Current at the shelfbreak (input into the slopewater system) and the eastward-flowing slopewater current over midslope (export out of the slopewater system). Particular attention is paid to the slopewater current, as this is a less well-known feature. The velocity structure of the slopewater current is different at the two longitudes, associated with a change in structure of the density front. Its mean transport is found to be significantly less than historical estimates. Both the lateral position and the strength of the current vary on long timescales. These fluctuations are correlated with the variability of the Labrador Current, as well as with changes in the deeper components of the slopewater (the Labrador Sea Water and Denmark Strait overflow water). The general picture that emerges is that the entire upper-layer slopewater circulation spins up/down on interannual timescales, coincident with strengthening/weakening of the overflow component of the deep western boundary current. Interestingly, more undiluted Labrador Sea Water is present in the spundown state.