Continental shelf water masses off the Jaguaribe River (4S), northeastern Brazil

This work analyzed temperature and salinity data obtained from two oceanographic cruises carried out over the western portion of the continental shelf adjacent to the Jaguaribe River in NE Brazil (May and October 2009) and included the rainy and dry seasons, which correspond to different levels of continental contribution to shelf waters. The results of the analysis identified three different water masses: River Water (RW), Coastal Water (CW) and Tropical Water (TW). During the period of maximum freshwater discharge, an estuarine plume that extended for 6km along the coastline was observed, and its influence could be felt over the inner shelf. The plume was associated with the presence of CW separated by a strong halocline. However, in the middle and outer shelf regions, the CW and the TW were observed below the 50m isobath, while the RW was not observed, most likely due to the presence of northeast trade winds that press the plume along the coast, reducing its seaward expansion. During the dry season, a higher influence of the TW was observed, most likely due to the space-time variability of the North Brazil Current (NBC) and the role of anticyclonic eddies that meander from the adjacent ocean towards the continental shelf. The results obtained suggest a strong seasonal influence upon the water mixing process along the continental shelf with the CW being affected by the RW and TW depending upon the season. •The estuarine plume extends to 6km along the coastline.•We observed an improvement of TW on the continental shelf during dry season.•The TW was restricted to depths greater than 50m in rainy season.•The high volume river in the rainy season fostered the formation of estuarine plume.•Physical division of the continental shelf east of Ceara State.