AN INTEGRATED APPROACH TO UNDERSTAND DISEQUILIBRIUM EFFECTS IN A STALAGMITE RECORD FROM A CENTRAL SIERRA NEVADA CAVE

Stalagmite records of stable isotope (δ¹⁸O_cc) variability from across the Southwestern United States change in-step with Northern Hemisphere temperature over the last deglaciation. The interpretations of δ¹⁸O_cc, however, is complicated due to the multiple influences on δ¹⁸O_cc. These influences include seasonality of precipitation, regional temperature change, and variability in precipitation source, among others. To isolate the influence of temperature in δ¹⁸O_cc records, we must develop quantitative and independent records of temperature. Here, we use a multi-proxy approach in a previously studied stalagmite, ML-1, from the central 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 δ¹⁸O_cc. We also use ML-1 fluid inclusions to create a record of 45 stable isotope measurements from the stalagmite fluid inclusions. The stable isotope results from the fluid inclusions reveal periods of anomalous temperature, d-excess, and fractionation at 18.0, 15.0, and 13.2 ka. To better constrain these periods, we use the forward proxy system model, Karstolution, integrated with isotope enabled climate modeling outputs of the western U.S. (iCESM1.3). The output of the Karstolution model reveals periods of disagreement between the predicted stalagmite record of δ¹⁸O_cc and the measured δ¹⁸O_cc from stalagmite ML-1 at 18.0, 15.0, and 13.2 ka. We interpret these integrated results as being caused by evaporative conditions and disequilibrium fractionation at these periods. Two of the three periods occur during warm interstadials during the deglaciation, suggesting that warm temperatures in California led to dry conditions in the central Sierra Nevada. This finding is in agreement with records of hydroclimate from across the Southwestern United States. The novel approach of integrating x-ray and neutron computed tomography, stable isotope measurements of fluid inclusions, and forward proxy system modeling, helps us understand the complex processes that impact stalagmite records of δ¹⁸O_cc in seasonal and arid climates.