Reconstructing precipitation variability in California using Sierra Nevada speleothems

Recent studies document the synchronous nature of shifts in North Atlantic regional climate, East Asian monsoon intensity, and precipitation in northern South America during the last glacial period. Yet questions remain as to what climate mechanisms influenced continental regions far removed from the North Atlantic and beyond the direct influence of the inter-tropical convergence zone. In the first three chapters of this dissertation, I develop multi-proxy, U-series-calibrated paleoclimate records from stalagmites from two central Sierra Nevada foothills caves that document precipitation changes that are approximately coeval with Greenland temperature changes during the last glacial period. The Moaning Cave stalagmite proxies record variations in precipitation between 16.5 and 8.7 ka. This record suggests drier and possibly warmer conditions, signified by elevated delta18O, delta13C, [Mg], [Sr], and [Ba], reduced dead carbon proportion, and more radiogenic 87Sr/86Sr, during Northern Hemisphere warm periods (Bolling, early and late Allerod) and wetter and possibly colder conditions during Northern Hemisphere cool periods (Older Dryas, Inter-Allerod Cold Period, and Younger Dryas). Similarly, paleoclimate proxy records from the McLean's Cave stalagmite, which precipitated between 68 and 56 ka, document drier conditions during interstadials and wetter conditions during stadials associated with the millennial-scale Dangsgaard- Oeschger temperature cycles noted in the Greenland ice core record. In the final chapter, I discuss observations of modern drip water variability in Black Chasm Cavern that support the interpretations of proxy records from Moaning and McLean's Cave stalagmites.The precipitation changes documented by the Moaning and McLean's Cave stalagmites are consistent with a broad picture of precipitation variability in the Northern Hemisphere in response to climate changes in the high northern latitudes. These records lend further support to growing evidence of strong connections between changes in ice extent at high northern latitudes and thermohaline circulation in the North Atlantic, and precipitation in western North America that persist despite changing boundary conditions throughout the last glacial period. Such relationships suggest that the Sierra Nevada region may see reductions in Pacific moisture under conditions of continued global warming, an occurrence that would have significant consequences in an area already characterized by marginally sufficient water resources.