Geological Society of America

T34 Advances in Nontraditional Stable Isotope Measurements and Utility as Proxies in Modern and Paleo-Settings (Posters)

Sunday, 22 September 2024
8:00 AM - 5:30 PM
Hall D

DEGLACIAL TEMPERATURE ESTIMATES FROM DUAL CLUMPED-ISOTOPE MEASUREMENTS AND FLUID INCLUSION NOBLE GAS CONCENTRATIONS IN A STALAGMITE FROM MCLEAN'S CAVE, WESTERN SIERRA NEVADA

Paper number: T34-5
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Cameron de Wet Presenting Author
Middlebury College, Middlebury, VT
Cameron de Wet Presenting Author
University of California, Davis, Davis, CA
Barbara Wortham
University of California, Davis, Davis, CA
Daniel A. Stolper
University of California Berkeley, Berkeley, CA
Ziman Wu
University of California Berkeley, Berkeley, CA
Kian Kafaie
University of California Berkeley, Berkeley, CA
Sujoy Mukhopadhyay
University of California at Davis, Davis, CA
Isabel Montañez
University of California, Davis, Davis, CA

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 a fluid inclusion noble gas measurement 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 measurement as well as using the Δ₄₇measurements 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. The majority 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.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-404536

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