Deglacial temperature estimates from dual clumped-isotope measurements and fluid inclusion noble gas concentrations in a stalagmite from McLean’s Cave, western Sierra Nevada

Abstract

Clumped-isotope (Δ47) measurements from speleothem calcite have the potential to record formation temperatures with an uncertainty of ± 2°C but are strongly impacted by kinetic effects during mineral precipitation that lead to isotopic disequilibrium and erroneously high-temperature estimates. The application of dual clumped-isotope (Δ47-Δ48) measurements can identify the influence of kinetic effects and has the potential to provide temperature estimates that are corrected for the degree of isotopic disequilibrium, though this involves a decrease in precision (± 4.5°C). The concentration of noble gases in water that is trapped in fluid inclusions in speleothems is another independent estimate of paleo-temperatures that is based on the temperature dependence of noble gas solubility in freshwater systems.   We combine these two newly emerging techniques by applying dual-clumped isotope (n = 15) and fluid inclusion noble gas measurements (n = 3) to a speleothem from McLeans Cave, located in the western foothills of the Sierra Nevada, that grew during the last deglaciation (~11 to 19 ka). We obtain temperature estimates using the noble gas measurements as well as using the Δ47 measurements for samples that do not exhibit isotopic disequilibrium in dual clumped-isotope space and compare these estimates with other western US temperature records from proxy records and climate model simulations. Many of the dual clumped-isotope samples, however do exhibit isotopic disequilibrium. We assess the degree to which disequilibrium can be corrected for using dual clumped-isotopes and test the sensitivity of these isotopic relationships to different published corrections to assess the implications for estimates of paleo-temperatures. Additionally, we compare the new dual-clumped isotope data with coeval d18O and d13C measurements, as well we previously collected measurements of d18O and d2H from fluid inclusions in the sample to investigate what processes may be driving the isotopic variability in both speleothem calcite and fluid inclusion water in this sample.