First direct measurements of currents on the continental shelf of Southern Brazil

We examine the first in situ velocity data collected on the shelf of Southern Brazil. The mooring station with two current meters was deployed at 32°41′S, 51°27′W on March 4, 1997, and recovered on August 2, 1997. Also analyzed are wind data for the same period obtained at a nearby coastal meteorological station. The observed velocity series can be interpreted as a sum of highly variable flow correlated with local wind stress and a “residual” mean current flowing northward along the shore at a few centimetres per second. In winter, the currents observed in the bulk of the water column exhibited a dramatic decrease in magnitude, as compared to the remainder of the series, although there was no similar decay of winds. We hypothesize that this is due to the impact of very stable salinity controlled winter stratification in a narrow subsurface layer because of enhanced river discharges that effectively isolates the deeper layers from atmospheric forcing. The frequency band corresponding to the periods from 2 to 10 days, presumably associated with meteorological forcing, dominated the velocity spectrum. The tidal currents were weak and predominantly diurnal.