Spatial and temporal variability of the Brazil‐Malvinas Confluence and the La Plata Plume as seen by SeaWiFS and AVHRR imagery

Abstract

Ocean color (OCTS, SeaWiFS) and sea surface temperature (AVHRR) images were used to evaluate spatial and temporal variability of the Brazil‐Malvinas Confluence and La Plata Plume (20° to 45°S and 40° to 65°W). The data set covers the period from January 1997 to June 2003. Chlorophyll and SST data were combined using Principal Component Analysis (PCA). The results yielded were used to identify and follow front displacements. PCA maps showed a close relationship with previous observations of currents behavior and the La Plata Plume. Firstly the analysis was performed on data retrieved from a monthly climatology, and the results show three remarkable features: a gradual increase of the northward intrusion of the La Plata Plume throughout the period lasting from summer to winter; the summer shape of the La Plata Plume showed a stronger penetration over the shelf on the Argentinean side of the estuary mouth; and the seasonal migration of the Brazil‐Malvinas Confluence. Monthly composites were then used and compared with discharge and wind data from scatterometers. The results show that increases on discharge led to a greater influence of the La Plata Plume over the continental shelf although during 1998 (El Niño) it did not penetrate farther north because of the unfavorable wind pattern (northerly). On the other side, during 2002, high discharge rates were associated with strong southerly winds, leading to a northern penetration of the plume. The same analysis was applied to daily images to show its application on locating the front's position. This analysis showed the same patterns.