The western boundary current in the Bransfield Strait, Antarctica

Abstract

The Bransfield Strait west of the Antarctic Peninsula has been considered as a highly productive region for all trophic levels from primary production, to zooplankton aggregations, especially krill, to birds and mammals. The western boundary current, referred to as the Bransfield Current, plays an important role in determining the transport and retention of biota in the Bransfield Strait. Following the study of surface current characteristics in the strait using 39 tracks of mixed-layer drifters deployed between 1988 and 1990, a high-resolution transect of temperature, salinity and current measurements crossing the Bransfield Current was conducted between 13 and 14 March 2004, for understanding its horizontal and vertical structure and dynamics. The results from current, temperature and salinity measurements using a vessel mounted narrow band acoustic doppler current profiler and conductivity–temperature–depth (CTD) sensors revealed the magnitude of this current of approximately 50 cm/s within a horizontal distance of 15 km associated with a narrow and deep density front 4–6 km wide and 500 m deep. The comparison between the direct current measurements and the geostrophic current estimates from the density field implies that the Bransfield Current is geostrophically balanced. The mechanism forming this current is explored with Sverdrup dynamics. Results indicate that the negative wind stress curl and β-effect lead to a southwestward transport in the Bransfield Strait. When this transport is restricted by land and shelves, a narrow western boundary current is formed.