¹⁷O_excess in Devils Hole calcite: an indicator of equilibrium fractionation and paleo moisture sources

Paleo-hydrology is typically based on measurements of δ¹⁸O in carbonate archives of environments on land. Triple oxygen isotopes (given as ¹⁷O_excess = 10⁶ [ln (10^–3 δ¹⁷O + 1) – 0.528 ln (10^–3 δ¹⁸O + 1)] in CaCO₃ has been recently shown to record ¹⁷O_excess of the carbonate parent water, thus providing additional paleo-hydrology information. Paleo rain-water ¹⁷O_excess, as recorded in speleothems, may be indicative of changes in moisture source location and evaporative conditions. The link between water and carbonate ¹⁷O_excess, as characterized by the fractionation slope θ (= ln¹⁷α / ln¹⁸α), has been determined in fast growing synthetic and biogenic carbonates, and in a few vadose speleothems. Here, we use the very slow growing mammillary calcite of Devils Hole to examine the fractionation slope at equilibrium, and to assess hypotheses of pluvial glacial periods in the Great Basin (USA). Results suggests that the equilibrium fractionation slope is consistent with that of fast-growing carbonates. ¹⁷O_excess values in Devils Hole paleo water are indistinguishable between glacial and interglacial extremes, as well as through Terminations II and IV. These reconstructed ¹⁷O_excess values are also similar to that of modern Devils Hole water (45 per meg). We interpret the observed ¹⁷O_excess to reflect significant continental recycling of the moisture reaching the inland site of Devils Hole during interglacials, but much reduced recycling during glacials.