Interannual variability of bottom temperatures in Drake Passage

A continuous 4 year record of in situ bottom temperature measurements at 3690 m within Drake Passage (59°43.7S, 55°29.5W) from November 1992 to November 1996 is presented. The record shows fluctuations of order 0.02°C over monthly periods throughout the 4 years, but the annual mean temperature is the subject under discussion in this work. Between June 1994 and May 1995 the water sampled was of the order of 0.1°C cooler than the water sampled on either side of this time period. This temporal temperature anomaly has only become apparent because of the availability of a continuous data set. Hydrographic data sampled from the same location as part of the World Ocean Circulation Experiment SR1 repeat section provide potential temperature and salinity values that enable the bottom temperature record to be linked to variability in Weddell Sea Deep Water (WSDW). Oxygen isotope measurements demonstrate that the year-long period of cooler WSDW measured in Drake Passage is a signature of Ice Shelf Water in the formation process of deep and bottom waters within the Weddell Sea.