Deep and Bottom Waters in the Eastern Scotia Sea: Rapid Changes in Properties and Circulation

Abstract

Two meridional hydrographic transects (in 1995 and 1999) across the eastern Scotia Sea are used to investigate variability in the deep and bottom waters between the South Scotia Ridge and South Georgia. There is a significant warming of the warm deep water (WDW) south of the southern boundary of the Antarctic Circumpolar Current (ACC); waters are approximately 0.1°?0.2°C warmer in 1999 than 1995. This is due mainly to raised WDW potential temperatures in the Weddell Sea being fed through to the Scotia Sea as the WDW flows northeastward in the Weddell Gyre. There is a warming of the Weddell Sea Deep Water (WSDW) of approximately 0.05°C across the whole extent of the section, and an accompanying change in salinity that maintains the potential temperature?salinity relationship. This is caused by variability in the properties of the water overflowing the South Scotia Ridge, rather than enhanced outflow of the bottom layer of the Scotia Sea or movements of the ACC fronts, and may be related to changes in the intensity of the Weddell Gyre circulation. Consideration of other works suggests that the colder WSDW of 1995 is likely to be the anomalous case, rather than the warmer WSDW of 1999. The 1999 section reveals an inflow of Lower WSDW from east of the South Sandwich Arc via the Georgia Passage; this is constrained to the south of the southern boundary, and is not apparent in the 1995 measurements. Meanders in the southern boundary at Georgia Passage are likely to play a role in controlling the inflow of Lower WSDW, although changes in the peak density of the WSDW flowing across the South Scotia Ridge may be important also, with a denser inflow from the south acting to preclude an inflow of similar density from the northeast.