Flow of bottom water in the northwestern Weddell Sea

Weddell Sea is known to feed recently formed deep and bottom water into the Antarctic circumpolar water belt, from whence it spreads into the basins o f the world ocean. The rates are still a matter of debate. To quantify the flow of bottom water in the northwestern Weddell Sea data obtained during f ive cruises with RN Polarstem between October 1989 and May 1998 were used. During the cruises in the Weddell Sea, five hydrographic surveys were carri ed out to measure water mass properties, and moored instruments were deploy ed over a time period of 8.5 years to obtain quasi-continuous time series. The average flow in the bottom water plume in the northwestern Weddell Sea deduced from the combined conductivity-temperature-depth and moored observa tions is 1.3+/-0.4 Sv. Intensive fluctuations of a wide range of timescales including annual and interannual variations are superimposed. The variatio ns are partly induced by fluctuations in the formation rates and partly by current velocity fluctuations related to the large-scale circulation. Takin g into account entrainment of modified Warm Deep Water and Weddell Sea Deep Water during the descent of the plume along the slope, between 0.5 Sv and 1.3 Sv of surface-ventilated water is supplied to the deep sea. This is sig nificantly less than the widely accepted ventilation rates of the deep sea. If there are no other significant sources of newly ventilated water in the Weddell Sea, either the dominant role of Weddell Sea Bottom Water in the S outhern Ocean or the global ventilation rates have to be reconsidered.