GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 89-13
Presentation Time: 11:15 AM


WORTHAM, Barbara E., Earth and Planetary Sciences, University of California at Davis, One Shields Ave, Davis, CA 95616, MONTAÑEZ, Isabel P., Earth and Planetary Sciences, University of California, Davis, One Shields Dr, Davis, CA 95616 and SWART, Peter K., Department of Marine Geosciences, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149

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.