COCCOLITHOPHORID BLOOMS IN THE GLOBAL OCEAN

The global distribution pattern of coccolithophorid blooms was mapped in order to ascertain the prevalence of these blooms in the world's oc eans and to estimate their worldwide production of CaCO3 and dimethyl sulfide (DMS). Mapping was accomplished by classifying pixels of 5-day global composites of coastal zone color scanner imagery into bloom an d nonbloom classes using a supervised, multispectral classification sc heme. Surface waters with the spectral signature of coccolithophorid b looms annually covered an average of 1.4 x 10(6) km2 in the world ocea ns from 1979 to 1985, with the subpolar latitudes accounting for 71% o f this surface area. Classified blooms were most extensive in the Suba rctic North Atlantic. Large expanses of the bloom signal were also det ected in the North Pacific, on the Argentine shelf and slope, and in n umerous lower latitude marginal seas and shelf regions. The greatest s patial extent of classified blooms in subpolar oceanic regions occurre d in the months from summer to early autumn, while those in lower lati tude marginal seas occurred in midwinter to early spring. Though the c lassification scheme was efficient in separating bloom and nonbloom cl asses during test simulations, and biogeographical literature generall y confirms the resulting distribution pattern of blooms in the subpola r regions, the cause of the bloom signal is equivocal in some geograph ic areas, particularly on shelf regions at lower latitudes. Standing s tock estimates suggest that the presumed Emiliania huxleyi blooms act as a significant source of calcite carbon and DMS sulfur on a regional scale. On a global scale, however, the satellite-detected coccolithop horid blooms are estimated to play only a minor role in the annual pro duction of these two compounds and their flux from the surface mixed l ayer.