Topographic control of thermohaline frontal structure in the Barents Sea Polar Front on the south flank of Spitsbergen Bank

Abstract

A combination of observations and process‐oriented numerical modeling is used to investigate the thermohaline structure of the Barents Sea Polar Front on the south flank of Spitsbergen Bank. The Polar Front is the boundary between warm, saline North Atlantic Water and cool, fresh Arctic Water located over the outer edge of the bank. Observations from the Barents Sea Polar Front Experiment in August 1992 show that North Atlantic Water was present in waters of 250 m or deeper, with little vertical structure beneath the upper 50 m of the water column. The mean velocity field over the south flank of the bank shows a westward flow of roughly 0.1 m s−1 in the North Atlantic Water and weak mean velocities over the outer edge of the bank. A primitive equation model is used with idealized bathymetry to show that the inflow of North Atlantic Water into the Barents Sea via the Bear Island Trough bifurcates at the sill between Nordkapp Bank and Sentral Bank, at the eastern edge of the Bear Island Trough. One branch of the North Atlantic Water recirculates westward, out of the Barents Sea and back into the Norwegian Sea. The flow of North Atlantic Water is barotropic and linear, following the bathymetry. The recirculating branch is sheared off at the sill, such that the core of recirculating flow is concentrated between the isobath coincident with the sill depth (∼260 m) and the center of the trough (∼500 m). Both the cross‐bank structure of the model thermohaline fields, as well as the along‐bank velocity, are very similar to the observations at a depth of 80 m. Thus the frontal structure is controlled by the interaction of the barotropic inflow with the sill at the eastern edge of the Bear Island Trough and is not controlled by processes occurring over the bank.