The deep waters from the Southern Ocean at the entry to the Argentine Basin

Hydrographic data from the World Ocean Circulation Experiment (WOCE) and So uth Atlantic Ventilation Experiment (SAVE) in the region of transition betw een the Scotia Sea and the Argentine Basin are examined to determine the co mposition of the deep water from the Southern Ocean that enters the Atlanti c, and to describe the pathways of its constituents. The deep current that flows westward against the Falkland Escarpment is formed of several superpo sed velocity cores that convey waters of different origins: Lower Circumpol ar Deep Water (LCDW), Southeast Pacific Deep Water (SPDW), and Weddell Sea Deep Water (WSDW). Different routes followed by the WSDW upstream of, and through, the Georgia Basin, lead to distinctions between the Lower-WSDW (sigma(4) > 46.09) and the Upper-WSDW (46.04 < sigma(4) < 46.09). The Lower-WSDW flows along the S outh Sandwich Trench, then cyclonically in the main trough of the Georgia B asin. Although a fraction escapes northward to the Argentine Basin, a compa rison of the WOCE data with those from previous programmes shows that this component had disappeared from the southwestern Argentine Basin in 1993/199 4. This corroborates previous results using SAVE and pre-SAVE data. A part of the Upper-WSDW, recognizable from different theta-S characteristics, flo ws through the Scotia Sea, then in the Georgia Basin along the southern fro nt of the Antarctic Circumpolar Current. Northward leakage at this front is expected to feed the Argentine Basin through the northern Georgia Basin. T he SPDW is originally found to the south of the Polar Front (PF) in Drake P assage. The northward veering of this front allows this water to cross the North Scotia Ridge at Shag Rocks Passage. It proceeds northward to the Arge ntine Basin around the Maurice Ewing Bank. The LCDW at the Falkland Escarpm ent is itself subdivided in two cores, of which only the denser one eventua lly underrides the North Atlantic Deep Water (NADW) in the Atlantic Ocean. This fraction is from the poleward side of the PF in Drake Passage. It also crosses the North Scotia Ridge at Shag Rocks Passage, then flows over the Falkland Plateau into the Atlantic, The lighter variety, from the northern side of the PF, is thought to cross the North Scotia Ridge at a passage aro und 55 degrees W. It enters the Argentine Basin in the density range of the NADW. (C) 1999 Elsevier Science Ltd, All rights reserved.