Deep and bottom waters in the eastern Scotia Sea: Rapid changes in properties and circulation

Two meridional hydrographic transects (in 1995 and 1999) across the eastern Scotia Sea are used to investigate variability in the deep and bottom wate rs 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 degrees -0.2 degreesC warmer in 1999 than 1995. This is due mainly to raised WDW po tential 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 degreesC across the whole extent of the section, and an accompanying change in salinity that m aintains the potential temperature-salinity relationship. This is caused by variability in the properties of the water overflowing the South Scotia Ri dge, 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 tha t the colder WSDW of 1995 is likely to be the anomalous case, rather than t he warmer WSDW of 1999. The 1999 section reveals an inflow of Lower WSDW fr om east of the South Sandwich Arc via the Georgia Passage; this is constrai ned to the south of the southern boundary, and is not apparent in the 1995 measurements. Meanders in the southern boundary at Georgia Passage are like ly 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 a n inflow of similar density from the northeast.