A Clumped Isotope Calibration for Lacustrine Carbonates

Friday, 19 December 2014
Bryce Akio Mitsunaga1, John Arthur Mering1, Victoria A Petryshyn1, Robert B Dunbar2, Andrew S Cohen3, Xingqi Liu4, Darrell S Kaufman5, Robert Eagle1 and Aradhna Tripati1, (1)University of California Los Angeles, Department of Earth, Planetary, and Space Sciences, Los Angeles, CA, United States, (2)Stanford University, School of Earth Sciences, Los Altos Hills, CA, United States, (3)University of Arizona, Department of Geosciences, Tucson, AZ, United States, (4)Capital Normal University, College of Environmental Resources and Tourism, Beijing, China, (5)Northern Arizona University, School of Earth Sciences and Environmental Sustainability, Flagstaff, AZ, United States
Our capacity to understand Earth’s environmental history is highly dependent on the accuracy of past climate reconstructions. Unfortunately, many terrestrial proxies—tree rings, speleothems, leaf margin analyses, etc.—are influenced by the effects of both temperature and precipitation. Methods that can isolate the effects of temperature alone are needed, and clumped isotope thermometry has the potential to be a useful tool for determining terrestrial climates. Multiple studies have shown that the fraction of 13C—18O bonds in carbonates is inversely related to the temperature at which the rocks formed and may be a useful proxy for reconstructing temperatures on land. An in-depth survey of lacustrine carbonates, however, has not yet been published. Therefore we have been measuring the abundance of 13C18O16O in the CO2 produced by the dissolution of modern lake samples’ carbonate minerals in phosphoric acid and comparing results to independently known estimates of lake water temperature and air temperature. Some of the sample types we have investigated include endogenic carbonates, freshwater gastropods, bivalves, microbialites, and ooids.