ISOTOPE PALEOECOLOGY OF THE MIOCENE PLANKTIC FORAMINIFERA GLOBOQUADRINA DEHISCENS AS INFERRED FROM INTERNATIONAL OCEAN DISCOVERY PROGRAM SITE U1510, SOUTHWEST PACIFIC

Globoquadrina dehiscens is a species of planktic foraminifera which lived during the Miocene Epoch. While this species has an easily recognizable test, the paleoecology of G. dehiscens from prior studies indicate it has a variable position in the water column. Little work has been done to determine if and how G. dehiscences changed location in the water column throughout its life history.

We inferred the dwelling depth of Globoquadrina dehiscens through its life cycle using stable isotopic analyses (δ¹³C, δ¹⁸O) of fossil specimens in six different size fractions from samples that span the Miocene Climatic Optimum at IODP Site U1510. From smaller to larger size fractions, the δ¹⁸O values of G. dehiscens increases, while the δ¹³C values increase. We also compared the stable isotopic values of G. dehiscens to those of mixed-layer and thermocline-dwelling species. The G. dehiscens stable isotopic data fell between and outside of the thermocline and surface dwelling data. Taken together, these results indicate that G. dehiscens descends to deeper depths during its life cycle, but its paleoecological signal may be obscured by high seasonality in the mid-latitudes, making it difficult to determine if G. dehiscens can be reliably used to reconstruct Miocene ocean conditions.