ENVIRONMENTAL CONTROLS ON BARIUM INCORPORATION INTO PLANKTIC FORAMINIFER, GLOBOROTALIA TRUNCATULINOIDES
We investigate environmental controls on Ba/Ca in the tests of Globorotalia truncatulinoides, a planktic species of foraminifera with a unique life history in the Gulf of Mexico (GoM). G. truncatulinoides experiences 92% of its annual flux to the sediment trap during winter (JFM) in the GoM. The Mg/Ca and ∂18O of the ontogenetic calcite suggests that primary calcification occurs within the surface mixed layer (0-150 meters), and a thick secondary crust is added at depths below the thermocline. We use LA-ICP-MS to analyze the Ba/Ca of both encrusted and non-encrusted G. truncatulinoides from a sediment trap time series in the GoM and find that the Ba/Ca in ontogenetic calcite of non-encrusted specimens varies between 10 and 200 mmol/mol, while the Ba/Ca of the secondary crust varies between 0 and 3 mmol/mol. The Ba/Ca of the non-encrusted G. truncatulinoides specimens is two to three orders of magnitude higher than that of co-occurring spinose planktic foraminifera (O. universa and G. ruber) in the GoM sediment trap, while the secondary crust has Ba/Ca similar to the spinose species. This suggests that the Ba/Ca of ontogenetic calcite in G. truncatulinoides is governed by fundamentally different processes, and does not necessarily reflect the Ba/Ca of seawater.