REMOTE-SENSING OF COCCOLITHOPHORE BLOOMS IN THE WESTERN SOUTH-ATLANTIC OCEAN

High-reflectance patches are regularly observed off the southeastern c oast of South America during the lat austral spring and summer in visi ble satellite imagery of the Coastal Zone Color Scanner (CZCS). Unfort unately, coincident in situ samples for identifying their cause are la cking. To ascertain the likelihood that these patches represent surfac e blooms of the coccolithophore Emiliania huxleyi, their distribution pattern was mapped and their spectral signature evaluated by classifyi ng 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 documente d cases, we conclude that the high-reflectance patches observed in sur face 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 su lfide sulfur. The bloom's production of these climatically relevant co mpounds and their alteration of optical properties in the surface laye r suggest that the blooms significantly affect the biogeochemistry and ecology of this region. (C) Elsevier Science Inc., 1997.