Gulf Stream meanders over steep topography

Abstract

Observations of the Gulf Stream thermocline as it meanders over the continental slope off Cape Hatteras are presented. Daily vertical sections of temperature and geostrophic velocity to 1500 m are calculated from an array of inverted echo sounders aligned across the Gulf Stream. These accompany time series of deep currents from a simultaneous array of bottom current meters. The vertical sections are computed using a previously derived technique which assumes the Gulf Stream variability is primarily first baroclinic mode. The sections reveal that the Gulf Stream front systematically shoals when it meanders offshore, an effect not observed farther downstream. This is accompanied by a compression of the main thermocline that in turn increases the core velocity of the jet but has little effect on overall transport. To explain this shoaling, the Gulf Stream is treated as a two‐layer flow; the lower layer vorticity balance suggests that the shoaling is caused by deep water columns preserving their layer thickness in the presence of the steep topography.