Direct measurements of western boundary currents off Brazil between 20°S and 28°S (original) (raw)

1998, Journal of Geophysical Research: Oceans

Current measurements from three moored arrays on the Brazilian continental slope between 20øS and 28øS are investigated for the existence and strength of western boundary currents from near the surface down to the North Atlantic Deep Water. The Brazil Current is found to deepen southward from 100 rn to more than 670 rn and to strengthen its volume transport to 16.2 x !06 m3/s. Antarctic Intermediate Water is transported in a well-developed boundary current southward at 28øS and northward north of Cabo Frio (24øS). This result supports earlier suggestions derived from the analysis of hydrographic data that Antarctic Intermediate Water enters the Brazil Basin from the east and bifurcates as it meets the continental break off Brazil. North Atlantic Deep Water is transported southward in a weakly developed boundary current that leads to lower estimates of volume transport than expected from earlier hydrographic data analysis. 1. Introduction The South Atlantic is known to be the highway on which the major interoceanic exchange of water masses and, consequently, of heat and salt occurs. As a result of the Meteor expedition 1925-1927 into the South Atlantic, Wast [!935] and Defant [1936a, b] illustrated the South Atlantic's deep and near-surface circulation, which in its general structure still holds for the subtropical western South Atlantic off Brazil. Much of the associated volume transports is carried in western boundary currents that in early theories are required to balance the interior ocean circulation [Stommel, 1948; Stommel and Aarons, 1960]. Principally, this concept could apply to all layers of deep and intermediate waters. For the Brazil Basin, one therefore would expect not only the near-surface Brazil Current balancing the wind-driven circulation, but also bound~ ary currents in the layers of the Antarctic Intermediate Water (AAIW), the Upper Circumpolar Deep Water (UCDW), the three layers of the North Atlantic Deep Water (NADW), and the Antarctic Bottom Water (AABW). While deep boundary currents carrying NADW southward and AABW northward have been described in the literature, a northward spreading of AAIW and UCDW within boundary currents has been less studied, and analysis was restricted to hydrographic data. For broad reviews of the present knowledge of the South Atlantic's water masses and general circulation as derived from hydrographic measurements, the reader is referred to Reid [!989], Peterson and Stramma [199!], DeMadron and Weatherly [1994], and Tsuchiya et al. [!994]. Few direct current observations were available from the boundary current system along the South American coast when the World Ocean Circulation Experiment (WOCE) began with its Deep Basin Experiment (DBE) in 1990. The then available records from moored current meters show the existence of a