T249 Cenozoic Evolution of Tropical Biota and Environments III: A Session Honoring the Contributions of Ann F. Budd

Tuesday, 3 November 2015
1:30 PM - 5:30 PM
Room 310

STABLE ISOTOPE EVIDENCE FOR DECLINING FRESHWATER INPUT TIED TO PLIO-PLEISTOCENE FAUNAL OVERTURN IN THE CARIBBEAN

Paper number: T249-1
Program: Technical Sessions
Time: 1:30 PM – 1:45 PM

Authors

Abstract

Faunal overturn in the Southwest Caribbean (SWC) during the Plio-Pleistocene has been primarily attributed to either decreased upwelling and productivity collapse associated with uplift of the Central American Isthmus (CAI; ~3.5 Ma), or decline in marine temperatures associated with Northern Hemisphere glaciation (NHG) beginning ~3.3 Ma. Extinction preferentially selected against taxa adapted to nutrient-rich environments uncommon in the SWC today, but the turnover acme occurred 1-2 myr after the final closure of the CAI, which is coincident with the onset of severe NHG. We use ~3000 new stable isotope measurements of ~60 serially-sampled gastropods (Conus and Strombus) from Costa Rica and Panama to examine nutrient delivery by upwelling and freshwater input during and after the final closure of the Central American Isthmus ~3.5 Ma. Gastropod δ18O profiles were referenced to an open-ocean baseline using δ18O values for planktonic foraminifera that lived near the same depth. Foraminiferal δ18O data for the Plio-Pleistocene were derived from sediment cores ODP 999A, DSDP 502B, and MD03-2628 in the Caribbean, and ODP 1242 in the Pacific. Deviation of δ18O profiles from baseline values allows quantification of seasonal upwelling and freshening in the nearshore environments.

δ18O profiles of fossil shells do not show the strong upwelling and freshening signals found in modern Pacific Conus profiles. However, SWC specimens older than ~2.5 Ma show δ18O ranges greater than those of modern specimens, suggesting potential refugia where seasonal upwelling and/or freshening enhanced productivity. The baseline approach points to significantly greater freshening from 2.5-3.6 Ma and no upwelling after 3.5 Ma. The freshening signal in SWC shells declines after 2.5 Ma, signaling a decline in nutrient delivery and providing a causal mechanism for delayed extinction in the SWC.