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Circulation, transport and bottom boundary layers of the deep currents in the Brazil Basin

Authors: Durrieu De Madron, X.; Weatherly, G.

Source: Journal of Marine Research, Volume 52, Number 4, 1 July 1994 , pp. 583-638(56)

Publisher: Sears Foundation for Marine Research

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Abstract:

Zonal and meridional hydrographic sections obtained for the South Atlantic Ventilation Experiment are used to study the circulation patterns and estimate the transports of North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) in the Brazil Basin.

The NADW Deep Western Boundary Current (DWBC) appears to be a relatively large (≈ 800 km wide by 2 km thick), double core current, separated by counterflowing recirculation. It appears to split, branching seaward at the Cape SaƵ Roque near 5S and again at the Columbia-Trinidad Seamount Chain at 21S. As a result of this latter bifurcation, the NADW DWBC flow in the southern basin decreases significantly.

In the southern part of the basin, the AABW DWBC is a relatively broad (≈ 1000 km), thin (≈ 700 m) flow which hugs the bottom of the continental rise. The densest waters that compose the core of the AABW DWBC eventually separate from the DWBC in the northern part of basin as they are topographically diverted to the east. The southward return flow at the eastern edge of the AABW DWBC and a northward flow in the eastern part of the basin suggest a meandering meridional recirculation of AABW in the interior of the basin. In the north central part of the deep basin there is a cyclonic abyssal gyre with a large component of Weddell Sea Deep Water (WSDW).

The along-isobath movement of the DWBCs over the sloping bottom drives cross-slope advection of the bottom boundary layer. The up-slope advection of denser water within the NADW DWBC is believed to set up a slippery bottom layer, while the bottom layer associated with the down-slope advection of lighter water within the AABW DWBC is estimated to be only partially slippery.

Geostrophic transports of heat, salt and mass are used to estimate mixing in the AABW flow in the Brazil Basin. The rates at which heat and salt mix are characteristic of diapycnal turbulent mixing. The mixing processes appear to be more active along the western boundary.

Document Type: Research Article

DOI: http://dx.doi.org/10.1357/0022240943076975

Publication date: July 1, 1994

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