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Koji Kameo:
Surface environmental changes in the Caribbean Sea during the Late Pliocene based on coccolith fluctuation records
(Poster)

Calcareous nannofossils of the Caribbean (Sites 998 and 999) and the eastern equatorial Pacific (Sites 844, 846, and 850) were examined to reconstruct palaeoceanographic changes during the Late Neogene related to the closing of the Isthmus of Panama. According to the comparison with assemblages among five sites, nannofossil assemblages between two Caribbean sites became similar after 2.7Ma, indicating the final closure of the Isthmus of Panama until 2.7Ma. Fluctuations of coccolith MARs (mass accumulation rates) of each species are calculated based on further quantitative analysis of the two Caribbean cores and reveal characteristic changes of calcareous nannofossil productivity and environmental changes in the photic zone throughout the Late Pliocene.

Some drastic changes of MARs of coccoliths are observed in the two Caribbean sites. Each change is characterised by great decreases and rapid increases of MARs of coccoliths that may be related to changes in surface productivity and preservation states of CaCO₃ at the ocean bottom. Approximately 2.7Ma, a great reduction of MARs of coccoliths began in the northern (Site 998) and southern (Site 999) Caribbean. In spite of no evidence of dissolution of coccoliths, a lower photic taxon (Florisphaera profunda) and other upper photic taxa decrease together at this point. This event clearly indicates that productivity in the photic zone became lower than in the previous age and may be influenced by rapid environmental deterioration of surface-conditions in the Caribbean, related to the completion of the Isthmus. After the nadir of low production of coccoliths in the Caribbean at 2.5Ma, a significant large production of coccoliths is observed between 2.4 to 2.1Ma. This great abundance of coccoliths corresponds to greater primary productivity, related to the globally-enhanced circulation systems.

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 [Division of Micropalaeontology] [Department of Geosciences] [Bremen University]

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