Recent temperature trends in the deep waters of the Weddell Sea

An analysis of the historical data set in the Weddell Sea encompassing CTD and bottle data from 1912 to 2000 showed warming of the Warm Deep Water (WDW) from the 1970's to 1990's at a rate of ~0.012 ±0.007 ^oC yr^-1. The Weddell Polynya of the mid-1970's preceded this warming and was associated with most of the coldest WDW temperatures observed. The warming was comparable to the global, average surface water warming observed by Levitus et al. [2000], to the warming of the WSBW in the central Weddell Sea observed by Fahrbach et al. [1998], and to the observed surface ice temperature warming from 1970 to 1998 in the Weddell Sea. The warming was not compensated by an increase in salinity and thus the WDW became less dense. The location of the warmest temperature was displaced towards the surface by ~200 m from the 1970's to the 1990's. The WDW warming was accompanied by a positive trend in the Southern Annular Mode (SAM) index. Although the average Weddell Sea Deep Water (WSDW) potential temperatures between 1500 and 3500 m were warmer in the 1990's than in the 1970's, high variability in the data prevented identification of a well-defined temporal trend. Warming of these Weddell Sea deep water masses has important implications for Antarctic Bottom Water (AABW) formation, melting of pack ice, and the regional ocean-atmosphere heat transfer.