UC Davis

Stalagmite records of stable isotope (18Occ) variability from across the Southwestern United States change in-step with Northern Hemisphere temperature over the last deglaciation. The interpretations of 18Occ records, however, is complicated due to the multiple influences on 18Occ. These influences include seasonality of precipitation, regional temperature change, and variability in precipitation source, among others. To isolate the influence of temperature in 18Occ records, we must develop quantitative and independent records of temperature. Here, I use a multi-proxy approach in a previously studied stalagmite, ML-1, from western Sierra Nevada. We employ high-resolution 3-dimensional neutron computed tomography and x-ray computed tomography to map fluid inclusion distribution in the stalagmite. Water-rich regions in ML-1 occur contemporaneously with the lowest values of 18Occ. We also use ML-1 fluid inclusions to determine a noble gas temperature for the Last Glacial Maximum (18.8  0.3 ka), indicating a 5.2  1.7 (2) C cooling relative to today. Noble gas concentrations were measured using a progressive step-crushing technique originally developed for understanding noble gas abundances in basalt. The progressive step-crushing technique and a robust water calibration reduces uncertainty in the resulting NGT relative to previous studies that utilize pre-crushing techniques. The temperature from the Last Glacial Maximum is used to correct for temperature variability in 18Occ. Variability in 18Occ is ~2.0 ‰ on the centennial scale originally interpreted to reflect temperature and precipitation source shifts. Finally, a record of 45 stable isotope measurements from the stalagmite fluid inclusions reveal periods of increased kinetic fractionation at 18, 15.2, and 13.2 ka. The results of the stable isotope analysis reveal that these periods are times of lower effective moisture locally. The combined results from these three approaches illustrate that, in the western Sierra Nevada, temperature variability only accounts for a fraction of total 18Occ changes on the centennial scale and points to variability in precipitation source region and effective moisture as major influences on stalagmite paleoclimate records. Additionally, I conclude that the central Sierra Nevada is sensitive to changing precipitation dynamics in the western U.S. that are teleconnected to circulation and temperature variability in the Pacific and the Atlantic.