FOSSILIZED DRIP-WATER FROM A SIERRA NEVADA CAVE REVEALS CHANGING CONDITIONS OVER THE NORTH PACIFIC DURING THE LAST DEGLACIATION

Speleothem calcite stable isotope values (δ¹⁸O and δ¹³C) are considered reliable proxies of regional climate. Previous studies have shown that δ¹⁸O can be used to interpret changing continental temperatures and precipitation dynamics. However, the δ¹⁸O of speleothem calcite is not a direct measurement of the δ¹⁸O of precipitation given that temperature affects the water-calcite isotopic fractionation. Fluid inclusion stable isotope values (δ¹⁸O and δ²H) are considered to be more representative of precipitation as fluid inclusions are the fossilized drip-water that promoted the growth of a given stalagmite. In turn, inclusion waters 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. We use fluid inclusions in a previously studied stalagmite from the western Sierra Nevada (ML-1) to reconstruct conditions over the North Pacific, a predominant precipitation source for California. Here we show that fluid inclusion δ¹⁸O and δ²H values from ML-1 are consistent with the modern local meteoric water line (δ²H = 7.8 x δ¹⁸O + 9.2) in warm periods but show a trend towards high d-excess values (35 to 70 ‰) during the Last Glacial Maximum (18.9 to 17.5 ka), the Older Dryas (14.5 to 13.5 ka), and the Younger Dryas (12.7 to 11.04 ka). Our results suggest that periods of cooler global temperatures led to high relative humidity gradients in the North Pacific, similar to, but more extreme than, the current seasonal cycle that occurs in the North Pacific. Additionally, snow meltwater and changing evaporation regimes may have additionally influenced fluid inclusion isotopic signatures at this site. This record improves our understanding of the ML-1 proxy δ¹⁸O record and provides new insight into changes in atmospheric conditions over the North Pacific during the last deglaciation.