LATE NEOGENE OCEANOGRAPHIC CHANGE ALONG FLORIDA WEST-COAST - EVIDENCEAND MECHANISMS

Evidence from vertebrate and invertebrate fossil assemblages and isoto pic analyses supports the hypothesis that during the Pliocene biologic al productivity in the eastern Gulf of Mexico was considerably higher than during the Pleistocene and Recent. Late Pliocene faunal changes i n the eastern Gulf, Western Atlantic, and possibly elsewhere may have resulted, at least in part, from this shift in productivity conditions . Even if marine temperatures declined, paleontological and isotopic d ata appear to require a change in productivity in the Late Pliocene. T his putative productivity decline may have been caused by some combina tion of causes at three geographic scales: (1) globally-marine product ivity may have fallen due to changes in continental weathering; (2) re gionally-North Atlantic productivity may have fallen as a result of in itiation of North Atlantic Deep Water formation (possibly a consequenc e of formation of the Central American Isthmus, CAI) and resulting net transfer of nutrients to the Pacific; (3) locally-productivity may ha ve fallen only in the eastern Gulf, due to circulation changes assiste d with the formation of the CAI, and an accompanying decline in upwell ing. The relative importance of processes at these three geographic sc ales remains unclear. The probable role of the formation of the CAI in two of the three, however, points to the importance of further invest igation of the paleoceanographic consequences of this event for Late C enozoic biological communities of the region.