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 database. Circumpolar Deep Water (CDW) was seen throughout most of the central basin and the western east basin, in contrast to earlier studies that have shown CDW being absent or only weakly present in the strait. In the western part 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 waters in the central and east basins that are distinct from one another and distinct from the surrounding deep waters outside the strait. The east basin has a more complex stratification than the central basin that must be the result of multiple sources. A model presented here explains the deep water in 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 predominate end-member. Analysis of the historic data shows that temperature and salinity within the central and east basins of the Bransfield have varied considerably over the past 30 years. A systematic change in the slope of the T–S relation in the central basin is observed, the result of the middepth water becoming colder and fresher. The east basin has also become colder and fresher over the past 30 years; however, this change has occurred uniformly 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 197