Conodonts and the Paleoclimatological and Paleoecological Applications of Phosphate Δ18O Measurements

Oxygen isotopic analysis of the phosphate in bioapatite has become a standard paleoclimatological tool with results documented in a rapidly expanding literature. Phosphate-based measurements are particularly important for samples where carbonates preservation is suspect (as is the case for many Paleozoic sites). Important analytical and observational advances that have fueled the expansion of phosphate-based studies include: 1) Oxygen isotopic ratios of biogenic apatite can be measured on small enough samples (≥ ~300 μg), quickly enough, cheaply enough, and accurately enough to permit meaningful high resolution paleoclimatic studies of trends through time, along spatial transects, and/or among taxa, 2) biogenic apatite is precipitated in approximate equilibrium with ambient waters and thus records the interplay of temperature and the isotopic composition of the water in which a sample grew, 3) tooth enamel and conodont crown material are quite resistant to diagenetic alteration and are preferred targets for both paleotemperature and paleoecological studies, 4) Paleozoic conodont δ18O records seem to provide robust paleotemperature information on time scales ranging from thousands of years to 100's of millions of years, and generation of increasingly refined paleotemperature records from this diagenetically resistant phase is likely to continue to be a useful field of study, 5) paleoenvironmental variations in δ18O values of seawater have been documented (e.g., differences between glacial and interglacial oceans), but whether and by how much the δ18O value of the hydrosphere may have increased since the Cambrian remains unresolved, and 6) differences in δ18O values among conodont taxa are increasingly well documented and, coupled with the potential to study growth series using ion microprobe techniques, are providing novel perspectives on and important tests of conodont paleoecology.