On the export of Antarctic Bottom Water from the Weddell Sea

A survey of the current field over the South Scotia Ridge, obtained with a lowered Acoustic Doppler Current Profiler (LADCP), is presented. There is a pattern of northward (southward) flow on the western (eastern) side of each of four deep passages in the ridge, which is supported by tracer measurements. The net full-depth LADCP-referenced geostrophic transport over the ridge is 22+/-7Sv (1 Sv = 10(6) m(3) s(-1)) northward, with the jets on either side of the passages transporting 5-10Sv in alternating directions. The corresponding Weddell Sea Deep Water (WSDW) transport over the ridge is 6.7+/-1.7 Sv. This is a factor of 4 larger than the only previous estimate in the literature, and suggests that a significant proportion of the Antarctic Bottom Water (AABW) invading the world ocean abyss escapes the Weddell Sea via the Scotia Sea. The net full-depth and WSDW transports over the ridge are modified to 7+/-6 and 4.7+/-0.7 Sv, respectively, by a box inverse model of the western Weddell Gyre. The model incorporates the WOCE A23 crossing of the central part of the gyre and a set of five constraints synthesizing our previous oceanographic knowledge of the region. It diagnoses that 9.7+/-3.7 Sv of AABW are formed in the Weddell Sea, and that comparable amounts are exported over the South Scotia Ridge (similar to48 %) and further east (similar to52%) assuming that no AABW enters the Weddell Gyre from the Indian Ocean. The WSDW fraction with neutral density gamma(n)>28.31 kg m(-3) transported over the ridge upwells in the Scotia Sea at a rate of 6x10(-6)m s(-1), an order of magnitude larger than many basin-scale estimates of deep upwelling in the literature. In contrast, the Weddell Sea Bottom Water exported to the eastern Weddell Gyre entrains upward at a rate of 8x10(-7) m s(-1), more typical of other open-ocean regions. When their different ventilation histories are considered, the comparable transports and disparate upwelling rates of the AABW exported over the South Scotia Ridge and farther east may be crucial to our understanding of teleconnections between the Weddell Sea and the global ocean. (C) 2002 Elsevier Science Ltd. All rights reserved.