Chlorophyll‐a variability off Patagonia based on SeaWiFS data

Seasonal to interannual variability of satellite derived chlorophyll‐a over the Patagonia shelf and shelf break in the western South Atlantic are studied based on 7 years of ocean‐color data (1998–2004) from the Sea‐Viewing Wide Field‐of‐View Sensor (SeaWiFS). Strong chlorophyll‐a seasonal variability (>4 mg m−3) is observed compared to the open ocean (<1.5 mg m−3). North of 45°S, chlorophyll‐a blooms initiate in early austral spring (September and October), while south of 45°S blooms begin in late spring to early summer (November through January). The spring maximum (>3.5 mg m−3) extends from the midshelf to the shelf break between 37°S and 44°S and southward to 51°S along a narrow shelf break band. In summer the shelf break maximum persists from 37°S to 51°S, and two inner‐shelf blooms develop off Valdés Peninsula and along a near‐coastal band between 46°S and 52°S (>3 mg m−3). Chlorophyll‐a concentrations in the northern midshelf sharply decay in late spring, reaching lowest concentrations in summer (February and March) and a secondary maximum in early winter (June). Though all regions present substantial interannual variations, the bloom locations are stable. The shelf break maximum is located inshore of the front between the low salinity shelf waters and the cold, salty, and nutrient‐rich Malvinas Current waters. The inner shelf maxima are offshore of fronts separating well‐mixed coastal waters from the stratified midshelf. North of 41°S the midshelf bloom is also associated to a bottom trapped thermal front. Thus, all the high chlorophyll‐a regions are associated to well‐defined fronts.