Horizontal and vertical motions associated with nonlinear mesoscale eddies influence upper ocean biological productivity by mediating the supply of nutrients into the euphotic layer. In the Brazil-Malvinas Confluence (BMC), a western boundary current region in the South Atlantic with intense mesoscale activity, eddy compositing of satellite near-surface chlorophyll (CHL) has revealed a dominance of monopoles with high (low) CHL concentrations inside cyclones (anticyclones). These patterns are attributed to eddy trapping of CHL and nutrients during eddy generation, coupled with a continuing vertical supply of nutrients and CHL during eddy intensification. In the BMC, there is uncertainty about the nature of the vertical advection associated with eddies. A negative cross-correlation has been found between anomalies of CHL and eddy Ekman pumping (W E), suggesting the action of other vertical transport mechanisms.
Using remote sensing and in situ data, we examine CHL and vertical velocity distributions within mesoscale eddies in the BMC. Recent improvements in both altimetric and satellite ocean color products allow us to track eddies and their associated surface chlorophyll signatures with high spatial and temporal resolutions. Eddy properties and composites of CHL anomalies and quasi-geostrophic vertical velocity (QG-w ) computed over a series of 5○×5○ BMC subregions reveal significant and unexpected heterogeneity for all variables. Monopole CHL anomalies are found in both cyclone and anticyclone composites; the anomalies are positive (negative) in the former (latter). The CHL anomalies are most intense in the northern and northwestern subregions, but become small (and non-significant) in the southern ones. Corresponding QG-w composites have dipole patterns of positive and negative advection. Maximum eddy composite QG-w values are found in the vicinity of fronts and sharp topographic gradients. In comparison with regional eddy composites, subregional composites have the potential to provide refined information about eddy dynamics and their associated biogeochemical variability.