Oxygen Isotope Fractionation in Marine Biogenic Phosphates Paleotemperature determinations are important in paleoclimatology, paleoceanography, and paleoecology. The goal of this research is to use isotopes to study recent and fossil material to determine ancient ocean temperatures in Paleozoic times. The use of oxygen isotopes in calcium carbonates is well established for determining paleotemperatures, but carbonates shells are susceptible to alteration. Phosphate minerals are more resistant to alteration and are present in a broad range of marine environments. This work will grow phosphatic brachiopods in the lab, and use the isotopic information from the controlled experiments as a possible model for ancient Paleozoic temperatures and environments.