The Gulf Stream—Barrier or Blender?

Abstract

The Gulf Stream ?60 hydrographic survey has been used to examine the distribution of water properties across the Gulf Stream as a function of potential density. This survey covered a half million square miles of Slope, Gulf Stream and Sargasso Sea Waters in the western North Atlantic. Quantities plotted as a function of density are acceleration potential, potential temperature, desso1ved oxygen and potential vorticity. The transition from Sargasso Sea Water to Slope Water in the upper thermocline (σ0<27.1) is sharp and coincides closely with the dynamical boundary of the Gulf Stream, defined by the gradient of acceleration potential. This indicates that water mass exchanges across the Gulf Stream-Slope Water front are limited at these levels. Below the 27.1 Σ0 surface, the gradient of acceleration potential still reveals the position of the Stream, but there is no coincident water man boundary. This and the uniformity of potential vorticity across the Stream suggest that the deep property fields are being efficiently homogenized by mesoscale exchanges across the Gulf Stream. A cross-frontal eddy diffusivity of KH=2.5?106 cm2 s?1 estimated from oxygen flux calculations agrees well with previously published values for frontal regimes.