NEOGENE PALEOPRODUCTIVITY OF THE CARIBBEAN AND EQUATORIAL EASTERN PACIFIC

This study examines paleoproductivity values determined from deep-sea benthic foraminifera from the late Oligocene (~26 Ma) to early Pleistocene (~2.5 Ma), and tests the hypothesis that paleoproductivity values prior to closure of the Central American Seaway are similar in both the Caribbean and equatorial Pacific, and then diverge around the time of early shoaling of the Isthmus of Panama. New data from Caribbean ODP Site 999 are examined in conjunction with previously published data from the Caribbean (DSDP Site 502) and Eastern Equatorial Pacific (DSDP Sites 503, 568, and 569). Identifications of benthic foraminifera in these previous studies were taxonomically standardized with newly prepared specimens before quantitative analysis. Paleoproductivity was measured with the proxies Benthic Foraminiferal Accumulation Rate (BFAR), the ratio of infaunal/epifaunal species (I/E), and relative abundances of mesotrophic, eutrophic and oligotrophic species. Prior to the differentiation in a bottom-water source for the Caribbean and Eastern Equatorial Pacific ~16 Ma, these two regions showed similar trends in organic carbon flux. The time of the initial differentiation in bottom water is marked in the Caribbean with a sharp decrease in BFAR to ~150 foraminifers per cm² per kyr, followed by a large increase to ~450 foraminifers per cm² per kyr. Larger-scale changes were not seen until 8 Ma, when constriction of the seaway occurred as indicated by previously measured isotopic shifts of Nd and Pb, changes in δ¹³C and δ¹⁸O, and benthic foraminiferal data. At that point, Caribbean values of paleoproductivity markedly decreased, as recorded by increases in oligotrophic indicator species, and diverged from equatorial Eastern Pacific values. With complete closure of the Central American Seaway at ~4 Ma, the Caribbean sites showed a decrease in BFAR values and thus paleoproductivity, supporting the conclusion that without surface exchange with the nutrient-rich equatorial Eastern Pacific, and with a large-scale decrease in Caribbean upwelling, the Caribbean Sea established its modern oligotrophic regime.