A Multifaceted Approach to Speleothem Paleoclimate Reconstruction During the Holocene and MIS 5: Construction of Traditional Proxy Records and Experimental Novel Proxy Development

Abstract

Increasing greenhouse gas concentrations in Earth’s atmosphere are moving the climate system into a state with no historical analog. Therefore, the study of Earth’s past climate beyond the instrumental record is fundamental for evaluating potential climate patterns, feedbacks, and tipping points that may play important roles in the future. Speleothems, or secondary cave carbonate minerals, are valuable archives of past climate because their geochemical structure preserves evidence of climate conditions when the minerals formed. The western United States is a water-stressed region at risk of more frequent and severe droughts due to future warming. Therefore understanding past climate change and the evolution of modern climate patterns in the region is critical in the effort to prepare for future changes in precipitation. Here, I produce new speleothem records documenting past precipitation and drought in northern Wyoming and northern California. The Wyoming records span the past 6000 years and show links between more frequent El Niño events in the Pacific and drought in the northern Rocky Mountains. These interpretations are supported by the results of a multi-year effort monitoring cave temperature, pCO2, drip rate, and drip water and modern calcite geochemistry. The northern California record is the highest resolution record of terrestrial hydroclimate from North America during the most recent interglacial period, which enables the evaluation of millennial-scale changes in climate not possible in other regional records. Lastly, I perform the first systematic, cave-analog based investigation of triple oxygen isotope measurements in speleothems. I show that critical information on water source history and trajectory can be transferred to the cave system and to the precipitating minerals under a wide range of cave temperature, pCO2 and drip rate. Overall, this dissertation encompasses multiple aspects of speleothem-based paleoclimate reconstruction and demonstrates the value of these records in assessing past and future climate change.