Observations of Shelf-Ocean Exchange in the Northern South Atlantic Bight Driven by the Gulf Stream

Abstract

Between Florida and Cape Hatteras, North Carolina, the Gulf Stream carries warm, salty waters poleward along the continental slope. This strong current abuts the edge of the South Atlantic Bight (SAB) continental shelf and is thought to influence exchange of waters between the open ocean and the shelf. Observations from a pair of instruments deployed for 19 months in the northern SAB are used here to examine the processes by which the Gulf Stream can impact this exchange. The instrument deployed on the SAB shelf edge shows that the time-averaged along-slope flow is surface-intensified with only few flow reversals at low frequencies (>40-day period). Time-averaged cross-slope flow is onto the SAB shelf in a lower layer and off-shelf above. Consistent with Ekman dynamics, the magnitude of lower-layer on-shelf flow is correlated with the along-slope velocity, which is in turn controlled by the position and/or transport of the Gulf Stream that flows poleward along the SAB continental slope. In the frequency band associated with downstream-propagating wave-like meanders of the Gulf Stream jet (2-15 day period), currents at the shelf-edge are characterized by surface-intensified flow in the along- and cross-slope directions. Estimates of maximum upwelling velocities associated with cyclonic frontal eddies between meander crests occasionally reach 100 m/day.