Vernal circulation in the Gulf of Maine

Abstract

The circulation in the Gulf of Maine has an important baroclinic component. It appears to be driven mostly by the density contrast between high‐salinity slope water which enters from the Atlantic and fresher waters which are formed in the Gulf or which enter from the Scotian shelf. Hydrographie surveys in three successive spring seasons suggest that slope water accumulates in Georges Basin, driving a counterclockwise surface circulation which brings Scotian shelf water westward into the Gulf and contributes to the eastward jet along the inner edge of Georges Bank. The slope water also crosses a sill and enters Jordan Basin, where it provides a potential energy source which may enhance a counterclockwise gyre partly driven by nearshore buoyancy sources and perhaps the wind. The coastal limb of the gyre turns offshore east of Penobscot Bay. Part of the separated coastal current recirculates in Jordan Basin, and part of it continues into Wilkinson Basin, generating a clockwise eddy as it passes over Jeffreys Bank. There is little evidence for recirculating surface flow in Wilkinson Basin. Instead, the surface water appears to split into branches feeding the Jordan Basin gyre, the Georges Bank jet, and an export path to Nantucket Shoals. The Jordan and Georges branches seem to be divided by the denser slope water in Georges Basin, and this may be the central process controlling the vernal intensification of the circulation in the Gulf. A more complete dynamical understanding awaits models which include the baroclinic influence of boundary waters.