On the influence of adequate Weddell Sea characteristics in a large-scale global ocean circulation model

Global ocean circulation models usually lack an adequate consideration of high-latitude processes due to a limited model domain or insufficient resolution. Without the processes in key areas of the global thermohaline circulation, the characteristics and flow of deep and bottom waters cannot be modeled realistically. In this study, a high-resolution (~20 km) ocean model focused on the Weddell Sea sector of the Southern Ocean is combined with a low-resolution (2°× 2°) global ocean model applying the state estimation technique. Temperature, salinity, and velocity data on two Weddell Sea sections from the regional model are used as constraints for the large-scale model in addition to satellite altimetry and sea-surface temperatures. The differences between the model with additional constraints and without document that the Weddell Sea circulation exerts significant influence on the course of the Antarctic Circumpolar Current with consequences for Southern Ocean water mass characteristics and the spreading of deep and bottom waters in the South Atlantic. Furthermore, a warming trend in the period 19932001 was found in the Weddell Sea and adjacent basins in agreement with float measurements in the upper Southern Ocean. Teleconnections to the North Atlantic are suggested but need further studies to demonstrate their statistical significance

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