Downstream Development of the Gulf Stream from 68° to 55°W

Abstract

Two CTD sections across the Gulf Stream at 68° and 55°W were acquired in late March of 1988 within 11 days of one another as part of an effort to look at downstream changes in the current. Using complementary current meter measurements, sections of total barotropic and geostrophic baroclinic velocity are constructed and used to calculate transport in potential density classes. Potential vorticity sections are presented for both locations, including the effects of planetary, stretching, and relative vorticity. The data are also used to examine the core properties of recently formed 18°Water at the two sections. It is found that: 1) water parcels in the exposed surface layers experience downstream density and potential vorticity changes consistent with surface forcing; 2) thermocline Gulf Stream transport is conserved downstream and below the exposed layers is conserved within individual density classes; 3) subthermocline Gulf Stream transport increases modestly at levels above the sill depth of the New England Seamounts but quadruples at levels below that; 4) the calculated potential vorticity structure is consistent with the transport distribution and historical observations and displays several distinct layers; and 5) transport and potential vorticity distributions together suggest that five active layers and steep bottom topography are required to fully describe downstream evolution of the Gulf Stream as an open-ocean eastward jet.