Stable isotope studies of fluid inclusions in speleothems and their paleoclimatic significance

Fluid inclusions found trapped in speleothems (cave deposited travertine) are interpreted as samples of seepage water from which enclosing calcium carbonate was deposited. The inclusions are assumed to have preserved their D/H ratios since the time of deposition. Initial 18O/16O ratios can be inferred from δD because rain- and snow-derived seepage waters fall on the meteoric water line (δD = 8δ18O + 10). Estimates of temperature of deposition of the carbonate can be calculated from inclusion D/H ratios and δ18O of enclosing calcite in Pleistocene speleothems. For most speleothems investigated (0–200,000 yr old) δ18O of calcite appears to have decreased with increasing temperature of deposition indicating that the dominant cause of climate-dependent change in δ18O of calcite was the change in Kcw, the isotope fractionation equilibrium constant, with temperature; δ18O of meteoric precipitation generally increased with increasing temperature, but not sufficiently to compensate for the decrease in Kcw.