Hydrography within the central and east basins of the Bransfield Strait, Antarctica

The hydrography in the central and east basins of the Bransfield Strait is examined using data collected along a track 340 km long through the strait in November 1995, in conjunction with historical data from the NODC databas e. Circumpolar Deep Water (CDW) was seen throughout most of the central bas in and the western east basin, in contrast to earlier studies that have sho wn CDW being absent or only weakly present in the strait. In the western pa rt of the central basin the CDW was present as a narrow band near Deception Island with strong thermal gradients at its southern boundary, consistent with previous observations. Local deep-water formation produces bottom wate rs in the central and east basins that are distinct from one another and di stinct from the surrounding deep waters outside the strait. The east basin has a more complex stratification than the central basin that must be the r esult of multiple sources. A model presented here explains the deep water i n the east basin as a mixture between the sill waters and deep waters from both the central basin and the Weddell Sea. Weddell Sea sill water is the p redominate end-member. Analysis of the historic data shows that temperature and salinity within the central and east basins of the Bransfield have var ied considerably over the past 30 years. A systematic change in the slope o f the T-S relation in the central basin is observed, the result of the midd epth water becoming colder and fresher. The east basin has also become cold er and fresher over the past 30 years; however, this change has occurred un iformly throughout the water column without affecting the slope of the east basin T-S relation. The changes in the east basin have been sporadic, with the largest change occurring between 1963 and 1975.