HOW DOES THE DEEP WESTERN BOUNDARY CURRENT CROSS THE GULF-STREAM

The manner in which the deep western boundary current (DWBC) crosses t he Gulf Stream is investigated using data from a hydrographic survey c onducted in 1990. Absolute geostrophic velocity vectors are computed u sing in situ neat data to obtain the reference level. Three density la yers are considered in detail: two mid-depth layers, which together ma ke up the shallowest water mass component of the DWBC (500- 1200 m), a nd a deep layer consisting of the Norwegian-Greenland overflow water ( 2500-3500 m). The shallowest layer does not make it through the crosso ver and is completely entrained by the Gulf Stream; however, the resul ting drop in equatorward transport is almost completely replenished by offshore entrainment just south of the crossover. In the intermediate laver, which is denser than the Gulf Stream coming off the shelf, par t of the DWBC recirculates to the northeast while the onshoremost port ion continues equatorward. In the deep layer only a small amount of re circulation occurs. The lateral fields of potential vorticity (Q) reve al a Q barrier associated with the Gulf Stream in the two mid-depth la yers, which is partially lessened in the intermediate one allowing the equatorward continuation of flow. In the deep layer, the DWBC maintai ns its potential vorticity through the crossover.