Seasonal variability of water masses and currents at the eastern Brazilian continental shelf (7.5-9∘ S)

The seasonal variability of water masses and currents of the Northeastern Brazilian continental shelf between 7.5-9∘ S are reported for the first time. Salinity and temperature data were collected during monthly hydrographic surveys between March/2012 and May/2013 across the shelf in the central part of the study area. Two broader surveys were carried out during winter (August/2013) and summer (January/2014) covering a total area of 4,600 km2. Water level and currents were also recorded with an acoustic Doppler current profiler (ADCP) moored near the mid-shelf (25 m) in the central area during the latter campaigns. The seasonal temperature variation ranged from 26 °C in September to 29.5 ∘C in April, with a two-month lag in respect to the minimum and maximum air temperature. The salinity did not present a clear seasonal variability, fluctuating between 36.5 and 37.0 psu throughout the year. The mean temperature and salinity from the campaigns in winter and summer were 26.5 and 27.6 ∘C and 37.1 and 36.7 psu, respectively. The Tropical Water (TW) was dominant, accounting for 95% to 97%, with presence of Coastal Water (CW) limited to the inner shelf. Colder waters were recorded at bottom along the shelf break indicating an upwelling process. The mean current speeds in winter and in summer were 0.11 and 0.06 m/s, respectively, reflecting the seasonal wind regime, more intense in winter. The currents in winter were predominantly northward, with short periods of southward inversions. These episodes were related with periods of along-shelf wind relaxation, potentially associated with atmospheric instabilities in higher latitudes. The currents during summer were sluggish and mainly southwards.