LAST GLACIAL MAXIMUM TO YOUNGER DRYAS PRECIPITATION VARIABILITY IN THE WESTERN SIERRA NEVADA

Calcite geochemical proxies (i.e. δ¹⁸O and δ¹³C of calcite; trace elements) typically applied to stalagmites are considered reliable records of regional terrestrial climate. However, variability in the cave environment and at the surface can confound calcite proxy signals, making the interpretation of specific processes challenging. Recent studies have documented that the stable isotope values (δ¹⁸O and δ²H) of fluids trapped as inclusions in stalagmites provide complementary information to calcite proxy records such as the isotopic composition of fossil drip water and quantitative cave air temperatures. In turn, inclusion fluids have great potential as proxies of paleo-precipitation δ²H and δ¹⁸O if a clear relationship between drip-water stable isotopic composition and local precipitation can be established. Here, we use a combination of computed tomography techniques to image and map the internal calcite structure and fluid inclusion distribution within a Sierra Nevada stalagmite (ML-1). Computed tomography results reveal that fluid is distributed in ML-1 independent of calcite density and/or fabric variability, demonstrating that water availability at the time of stalagmite growth controls fluid inclusion distribution. Moreover, fluid inclusion δ¹⁸O and δ²H values are consistent with the modern local meteoric water line (δ²H = 7.8 x δ¹⁸O + 9.2) for subsequent interstadials of the last deglaciation (Bölling/Allerød; 14.5 to 12 ka, n=8) but are more negative (Δδ¹⁸O ~ 4 ‰;Δδ²H ~ 20‰) and more variable during the LGM (18.9 to 17.5 ka, n=5) and ensuing stadial (Heinrich 1; 17.5 to 14.5 ka, n = 17). Our results suggest that during the last glacial maximum, more intense storms and/or storms from further afield sources delivered precipitation over the cave. Notably, during the deglaciation, precipitation amount decreased and evolved to a modern regime. The analysis of fluid inclusions in stalagmites have the potential to reveal new information and contribute to deconvolving the multiple influences on calcite proxy signals.