Ostracod shell chemistry — overview

Abstract

© 2002 by the American Geophysical Union. Ostracod shells are valuable sources of calcite for geochemical analysis. Over the past two decades, research has provided much insight into the controls on traceelement partitioning and stable-isotope fractionation into ostracod shell calcite both in non-marine and marine settings. This chapter provides an overview of the controls and illustrates the application of the techniques to environmental reconstruction using examples. Trace-element work has concentrated on Mg and Sr uptake, which relate to water chemistry and temperature, both in lakes and the oceans. Oxygen- and carbon-isotope analyses of ostracods have concentrated on lacustrine environments, from which other carbonate microfossils are largely absent. In hydrologically- closed lakes, especially in dryland regions, geochemical signatures provide information on variations in hydrology, and may reflect changes in effective precipitation. In temperate deep lakes with an isothermal hypolimnion and negligible evaporative enrichment, isotopic analyses of benthic ostracod shells reflect the isotopic composition of lake water, which may reflect the regional precipitation signal. In shallow hydrologically-open lakes, geochemical signatures are more complex, although Mg content of ostracod shells may reflect water temperature, provided lake-water ionic composition has not changed. In marginal-marine environments, ostracod shell chemistry may indicate salinity changes that arise from mixing of marine and meteoric waters. Finally, in the deep oceans, the Mg content of benthic ostracods reflects ocean bottom-water temperature. In addition to these well-established approaches, ostracod shells also have potential as indicators of past metal pollution in the aquatic environment through measurements of heavy metal content of the shells, and as material for dating.