The boundary currents in the western Argentine Basin

Abstract

A quasi-synoptic hydrographic data set enclosing the Brazil-Falkland (Malvinas) Confluence Zone is used to investigate the absolute geostrophic volume transports of the western boundary currents in the region. Water mass characteristics provide a basis for adjusting geostrophic shears near the continental margin at 38°S, and the depth-integrated southward transport there, comprised of the Brazil Current and deep boundary flow, is estimated to be 68 Sv (1 Sv = 10 6 m 3 s −1). Of this, 26 Sv are thermocline water, 18 Sv are Antarctic Intermediate Water, and 24 Sv are deep waters of circumpolar and North Atlantic origin. Assuming the bottom flow is parallel to the steep bathymetry at the western boundary of the Argentine Basin, a geostrophic transport of 143 Sv is found to move seaward across the 4600-m isobath between the latitudes of 38° and 46°S. Top-to-bottom northward transports in the region of the Falkland Current are then solved as residual quantities from mass balances for enclosed areas. The likelihood of significant northward bottom velocities in deep western boundary currents there, combined with there being no apparent reversals within the water column in the direction of flow, makes such a procedure necessary. The resulting estimates for the depth-integrated northward transports in the Falkland Current region are 75 Sv at 42°S and 88 Sv at 46°S. Approximately 60 and 70 Sv, respectively are contained in the upper 2000 m as a direct extension of the northern Antarctic Circumpolar Current, while 34 and 40 Sv are contained in the density range of surface and intermediate waters. The northward transports in layers beneath the 2000-m level belong to the deep western boundary currents of the southern Argentine Basin. These numbers for the Falkland Current region are much larger than the 10–20 Sv values typically found in the literature, but they are consistent with other information such as the volume transport in the upper 2000 m of the northern Antarctic Circumpolar Current in Drake Passage, velocities of surface drifters in the Falkland Current, and the full-depth circulation in the interior of the Argentine Basin.