Mixing of shelf, slope and Gulf Stream water over the continental slope of the Middle Atlantic Bight

Abstract

A combination of water masses was observed over the continental slope between Cape Hatteras and Hudson Canyon following the passage of a Gulf Stream meander. It was largely made up of fluid discharged from the Gulf Stream in the wake of the meander and also contained intrusions of Middle Atlantic Bight (MAB) shelf water and slope water. Its most prominent dynamical feature was an anticyclonic eddy that had an initial diameter of about 100 km but contained relatively weak currents, not greater than 30 cm s −1 in magnitude. Discharged Gulf Stream water made up the eddy's core, and a band of entrained shelf water circulated at its margin. This band was connected with another entrained shelf water band that flowed along the northern margin of the Gulf Stream. Transport of the shelf water at the edge of the eddy was estimated to be 1.3 × 10 5 m 3 s −1, which is comparable with the estimated alongshore transport of water over the MAB shelf. Vigorous mixing of both shelf water bands with surrounding discharged Gulf Stream water is indicated by the large differences of the latter's T/S properties from those found within the Gulf Stream. These differences were used to estimate salt fluxes into the shelf water band at the edge of the anticyclonic eddy, with results in the range of 1.9–6.6 × 10 −6 g salt cm −2 s −2. Density ratios and Richardson numbers determined from hydrographic data suggest that these salt fluxes were primarily the result of mixing by double diffusive processes, and that shear-induced turbulence combined with double diffusion to effect vertical mixing at the margins of the shelf water band next to the Gulf Stream.