Chlorophyll variability and eddies in the Brazil-Malvinas Confluence region

Ocean-color data from Sea-viewing Wide Field-of-view Sensor (SeaWiFS) have been used to investigate temporal and spatial variability of chlorophyll-a concentration in the Brazil-Malvinas Confluence (BMC) region (30-50degreesS and 30-70degreesW). Our analysis is based on 60 monthly averaged and 230 weekly averaged images (9 x 9 km(2) resolution) that span from October 1997 to September 2002 in the Southwestern Atlantic Ocean. A nonlinear model was used to fit the annual harmonic of the chlorophyll concentration anomalies in the region. Analysis of the spatial variability of model parameters has shown the existence of a marked annual cycle at several locations in the study region. We also have observed shorter-period oscillating features on smaller spatial scale, associated with the BMC dynamics. These mesoscale features have periods of about 9-12 weeks and have a marked northward propagation with higher chlorophyll values relative to the surrounding waters. Further investigation of these mesoscale features with an advanced very high-resolution radiometer thermal infrared and TOPEX/POSEIDON (T/P) altimeter data has unveiled interesting eddy-like surface structures in the BMC region. These multiple eddies are clearly visible on both thermal and color imagery off southern Brazil. Furthermore, the SeaWiFS images have shown a decrease in chlorophyll-a concentration as these eddies propagate northward, due to mixing with chlorophyll-poor tropical waters carried southward by the Brazil Current. Several rings along the shelf region, which are probably generated by shear instabilities, also have been detected by the ocean-color images. (C) 2004 Elsevier Ltd. All rights reserved.