Seasonal variation of the water masses structure in the Amazon continental shelf and adjacent oceanic area

Abstract

This work analyzes hydrographic properties (temperature and sal inity) obtained from three oceanographic cruises performed along the Amazon continental shelf and adjacent oceanic areas of the western equatorial Atlantic, Field data covered three distinct periods and river discharge situation: the maximum river outflow during boreal spring (May 1999); the transition flow period (maximum to minimum discharges) during summer (August 2001), and minimum river flow during autumn (November 1997), The analysis of CTD hydrographic profiles identified four water masses: Coastal Water (CW), Tropical Surface Water (TSW), South Atlantic Central Water (SACW) and Antarctic Intermediary Water (AIW), Results suggest that wind shear variability acts over the horizontal distribution of surface water masses (CW and TSW), while the subsurface waters (SACW and AIW) are influenced by seasonal variability of the NBC transport and the presence of anticyclonic rings at the NBC retroflection area, Vertical transects analysis show that SACW is strongly expanded during the transition river flow regime (about 70 m at 49°W and 220 m at 50°W), which corresponds to the period when NBC and North Equatorial Countercurrent (NECC) reach their maximum strengths. © 2005 Sociedade Brasileira de Geofísica.