UC San Diego

The progressive closing of the Central American Seaway (CAS) from initial shoaling in the mid-Miocene (̃13 Ma) to final closure in the late Pliocene (̃3-2.7 Ma) substantially altered the surface salinity, nutrient content, and biology of the Caribbean Sea and eastern equatorial Pacific Ocean (EEP). Studies of fossil plankton, reef development, and oceanographic models of the shoaling Isthmus of Panama suggest that there was a distinct drop in Caribbean productivity with closure of the seaway, whereas models of the EEP suggest a marked increase in production. However, there has not been a detailed comparison of export production records between the two ocean basins. Here, we present the highest resolution paleoproductivity proxy records to date for the Caribbean and EEP, which suggest that the formation of the Isthmus of Panama had little direct effect on nearby productivity levels. Instead, export production in both basins was governed mostly by high latitude nutrient sources, as seen in the spectral dominance of high latitude orbital forcing. Export production gradually decreased in the Caribbean starting about 2.7 Ma, while remaining relatively stable in the EEP. Caribbean export production falls mostly during glacial phases in response to ventilation of the tropical thermocline by increasingly nutrient-starved Glacial North Atlantic Intermediate Water. Our findings may suggest a sensitivity of low- latitude productivity to future anthropogenic climate forcing at the high latitudes. In addition, the gradual intensification of Caribbean oligotrophy may be responsible for the well-documented delay in extinction of Caribbean reef-associated fauna relative to the CAS closure