CARBONATE STABLE ISOTOPES | Speleothems

The oxygen isotopic composition of calcite speleothems (stalagmites, etc.) can be used as a record of changing climate. In deep caves, calcite grows in isotopic equilibrium with drip water and, if δ18O of past drip waters were known, could provide paleotemperatures for caves, equivalent to average surface temperature above the cave. Isotopic records can be dated with high precision by U series up to 500,000 years. Equilibrium O isotope records have been widely used as relative climate indicators by comparison with other climate archives (δ18O in ice cores and foraminifera). Carbon isotope (δ13C) variations reflect changes in vegetation above the cave. Fluid inclusions in speleothem represent trapped drip waters, from which H isotope (δD) records can be used to estimate δ18O of paleowaters.