Circulation in the western South Atlantic shelf and1export to the deep
adjacent ocean -30 to 40{degree sign} S
Abstract
High sea surface chlorophyll concentration on the Argentine Continental
Shelf (ACS) frequently extends to the deep ocean in the vicinity of the
Brazil/Malvinas Confluence (BMC). The offshore transport of shelf waters
likely plays a key role in the biogeochemical balance of the western
South Atlantic and promotes the offshore transport of planktonic
species. We analyze data from an oceanographic survey carried out in the
western South Atlantic shelf between 31° and 38°S in October 2013. We
describe the distribution and circulation of the water masses and focus
on the exchanges with the open ocean. On-shelf subsurface intrusions of
oceanic waters and river discharge supply nutrients to the shelf. A
low-salinity tongue of Río de la Plata (RDP) waters extends northward to
32°S. Below these waters Subantarctic and Subtropical Shelf waters
(SASW, STSW) meet to form the Subtropical Shelf Front. The main SASW
branch, oversaturated in oxygen and with high-fluorescence mixes with a
detachment of Brazil Current waters at 38°S and is exported offshore
along the BMC. A second branch of SASW reaches 33°S mixing along its way
with RDP and STSW, and returns southward after splitting into an onshore
and an offshore branch. The offshore branch is exported to the open
ocean through the BMC. These export routes are in overall qualitative
agreement with those indicated by a high-resolution reanalysis. We
estimate a net off-shelf transport (geostrophic plus Ekman) of 3.33Sv to
the open ocean between 32.1° and 37.7°S. The majority of the offshore
flow occurs between 34.7° and 37.7°S.