On the Deep Western Boundary Current south of Cape Cod

Abstract

Abstract Using CTD/oxygen data from eight cruises in the decade from 1994–2003, we have constructed a mean ‘section’ of properties across the Deep Western Boundary Current (DWBC) south of Cape Cod near 70°W. Since all sections included direct velocity measurements, our composite section enables us to portray the flow field as well as the mean water mass structure. Inshore of the Gulf Stream between the 2500 and 4000 m isobaths, the flow is to the southwest along the bathymetry and is remarkably barotropic. The equatorward flowing Labrador Sea Water is shown to have high dissolved oxygen, low salinity, and low potential vorticity, while the underlying Overflow Water is high in oxygen. Transport estimates for the cold limb of the thermohaline circulation give a range of −14 to −19 Sv for the N. Atlantic Deep Water found on the section. The greatest uncertainty is due to the presence of a Warm-Core Ring on one of the sections, which apparently completely reversed the flow in the DWBC. Offshore of the DWBC, some of the deep source waters are returned to the north in the deep Gulf Stream. The section is compared to two other, widely separated locations (Abaco and 55°W) that have markedly different DWBC characteristics.