A STABLE ISOTOPE AND TRACE ELEMENT APPROACH TO UNDERSTANDING TEMPERATURE AND SALINITY CHANGES IN THE CARIBBEAN DURING PLIOCENE

The emergence of the Isthmus of Panama and constriction of the Central American Seaway (CAS) ~3.5 Ma has been attributed to the establishment of the present-day salinity contrast between the Caribbean and eastern equatorial Pacific surface ocean waters, increased transport of atmospheric heat and water vapor to higher northern latitudes and concomitant intensification of Northern Hemisphere Glaciation (NHG), and an extinction event which preferentially targeted benthic faunal communities adapted to eutrophic conditions sporadically prevalent in the southwestern Caribbean (SWC) today. Previous studies have indicated that the Caribbean turnover was either associated with reduced upwelling (and hence, decline in the productivity in shallow Caribbean waters) or decrease in marine temperatures associated with NHG. Isotopic analysis for stable isotopes of carbon and oxygen have been performed on both modern and fossil gastropod (Conus and Strombus) shells to differentiate and quantify the upwelling and freshening signals in SWC across the time interval of establishment of the isthmus (Tao et. al. (2013) and Grossman et. al. (in prep.)) using the ‘baseline approach’. This study intends to refine the existing methodology for paleobathymetric and paleosalinity interpretations by utilizing foraminiferal Mg/Ca to isolate the temperature effect from the salinity signal revealed by δ¹⁸O in order to minimize complexities associated with baseline referencing and further bolster distinction between the upwelling and freshening signals. Additionally, in order to characterize the source of nutrient influx (terrestrial and/or deep marine) in the SWC as well as the strength of freshening and/or upwelling, δ¹⁵N values from fossil gastropod (Conus and Strombus) shells will be studied. Nitrogen as a proxy for organic-rich surface waters in the SWC will further be used to quantify the gradual decline in nutrient delivery across the phase of closure of the CAS and verify the potential for nutrient-rich waters to exist in confined pockets (refugia).