On the Interaction between the Gulf Stream and the New England Seamount Chain

Abstract

In the course of numerical simulations with a primitive equation regional model of the Gulf Stream, bottom topography and the New England Seamount Chain (NESC) in particular show significant influence on the variability and the energetics of the Gulf Stream system. The model is an eddy-resolving, coastal ocean model that includes thermohaline dynamics and a second-order turbulence closure scheme to provide vertical mixing coefficients; it is driven at the surface by observed monthly wind stress and heat fluxes. The surface and the deep variabilities obtained from the numerical simulations are in fair agreement with the observed variabilities inferred, for example, from the Geosat altimetry data and from measurements of eddy kinetic energy (EKE). To study how the NESC affects the Gulf Stream dynamics, a control run without the NESC (however, leaving the other topographic features such as the continental shelf and slope intact) is compared to simulation with full bottom topography. According to the model results, the effects of the NESC on the Gulf Stream include southward deflection of the stream as it passes across the NESC and the development of several quasi-stationary, nearly barotropic recirculation cells on both sides of the Gulf Stream. Another result is an increase in the mean kinetic energy (MKE) and a decrease in the EKE in most of the water column as a result of the inclusion of the NESC. The inclusion of the NESC causes an upstream shift in the area of maximum variability compared with the case without the NESC; the maximum deep EKE is thus obtained upstream of the NESC. This study suggests that the stabilizing effects of the bottom topography dominate over possible destabilizing effects due to increase in meander amplitudes near the NESC. This study also suggests that the NESC causes a downstream decrease in the propagation speed of meanders upstream of the NESC and the development of an almost steady, large meander downstream of the NESC.