Remote sensing of coccolithophore blooms in the western South Atlantic Ocean

High-reflectance patches are regularly observed off the southeastern coast of South America during the lat austral spring and summer in visible satellite imagery of the Coastal Zone Color Scanner (CZCS). Unfortunately, coincident in situ samples for identifying their cause are lacking. To ascertain the likelihood that these patches represent surface blooms of the coccolithophore Emiliania huxleyi, their distribution pattern was mapped and their spectral signature evaluated by classifying CZCS imagery with a supervised, multispectral classification scheme that had been developed to detect this phytoplankton species. On the basis of the similarity of these characteristics to those of documented cases, we conclude that the high-reflectance patches observed in surface waters of the shelf and beyond are E. huxleyi blooms. The blooms seasonally occupied an area as large as 550,000 km(2). Standing stock estimates indicate that the detected blooms produce an average of 1.5-4.9X10(5) metric tons of calcite carbon and 4.0X10(3) t of dimethyl sulfide sulfur. The bloom's production of these climatically relevant compounds and their alteration of optical properties in the surface layer suggest that the blooms significantly affect the biogeochemistry and ecology of this region. (C) Elsevier Science Inc., 1997.