Circulation and zooplankton biomass distribution over the southern Patagonian shelf during late summer

In this article we use hydrographic data collected in the period 1994–2000 to analyze the summer distributions of temperature and salinity in the southern Patagonian shelf (Argentina). The objective is to infer the circulation patterns of the Patagonian shelf and to relate them to the zooplankton biomass distribution. The vertical structure of the hydrographic variables indicates the existence of two distinct regions. North of 51°S, the water column can be characterized as a two-layer system separated by a thermocline at approximately 50 m depth. South of 51°S, the density structure of the water column is nearly homogeneous. The two regions are separated by a front that extends in a northeast direction from the coastal region of the Grande Bay towards the continental slope. The circulation patterns inferred from the observed fields indicates that although the circulation in the southernmost portion of the Patagonian shelf, i.e., from Tierra del Fuego to the Grande Bay front, is towards the north, as predicted by previous studies, this northward flow turns offshore at the location of the Grande Bay front. This frontal region and the associated circulation pattern have not been previously described. The inferred circulation may enhance zooplankton production and accumulation over the coastal area of the Grande Bay—via increased primary production, by favoring both the enrichment and trapping of nutrients, and the retention of organisms.