Space—Time Variability of the Deep Western Boundary Current Oxygen Core

Abstract

Twelve historical CTD/oxygen sections between the Grand Banks and Cape Hatteras, occupied over the time period 1981?85, are analyzed to investigate the variability of the Deep Western Boundary Current (DWBC) property core. The sections are transformed into a coordinate system of bottom depth versus height above the bottom, then interpolated onto a regular grid in order to facilitate an inter-sectional comparison. The average sections show a high-oxygen core near 3200-m depth, ? = 2.2°C, which corresponds to a region of upward sloping isotherms against the boundary, inshore of the deep Gulf Stream. As the DWBC progresses toward Cape Hatteras it shoals significantly and becomes less dense as a result of mixing with surrounding fluid along its path. There is, however, much scatter about this general alongstream trend and large density fluctuations are correlated with changes in bottom depth and cross-sectional area of the DWBC core. This variability is most likely the downstream response to changes in the overflow source waters of the DWBC. Some of the DWBC appears to recirculate with the deep Gulf Stream near Cape Hatteras (where the two currents cross each other), forming a weaker offshore oxygen core.