9709964 Smith The study of high-resolution proxy climate records covering interannual through millennial time scales is growing importance in the field of global climate change. Many of these proxy climate records include isotopic and trace-element geochemical data derived from fossil ostracode shells in continental deposits, such as lakes, springs, and wetlands. Ostracodes (microscopic crustaceans) play a role similar to that of foraminifera in the marine world by providing vital information about the interactive nature of climate and the hydrologic cycle through their ecology, shell geochemistry, and biogeographical distribution. In fact, ostracodes are the primary calcareous microfossils in continental records. Despite the increasing amount of research presently underway involving oxygen isotopes and ostracode shell geochemistry in continental records, there is significant gap in the knowledge base. There are no existing studies available that provide, through both field and laboratory calibration, the modern relationship between isotope fractionation and ostracode isotopic composition will remain at best a qualitative indicator of past conditions. The high resolution continental climate records that rely on ostracode isotopic information have at present no quantified basis for interpretation. We propose to conduct both field and laboratory calibration studies of ostracode species and shell chemistry. This research focuses on modern distributions of ostracodes and their isotopic and trace-element signatures, with the purpose of developing them as proxy indicators for past Earth system processes. The field-based study will calibrate ostracode species distributions and shell chemistry ((18O, (13C, Mg/Ca, Sr/Ca), against hydrochemistry (cation, anion, TIC, (18O, (D, (13C of DIC) and climate data. This will include a study of intra-and inter-annual variation. The laboratory-based study will verify the oxygen-isotope and trace element fractionation behavior of several common spe cies of ostracodes as a function of hydrochemistry and temperature. The results of this study will provide, for the first time, experimental verification through both field and laboratory calibration, of ostracode isotopic and trace-element composition as a quantifiable indicator for paleoclimate analysis . Basic issues revolving around seasonality, hydrochemical variability, vital effects, and different hydrologic regimes will have been examined and assessed. A fundamental gap in the paleoclimate knowledge base will thus be filled.
