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Stable and Clumped Isotope Analyses of Last Glacial Maximum Pluvial Lakes to Constrain Past Hydroclimate


The Last Glacial Maximum (LGM; ~23,000-19,000 years ago) and subsequent deglaciation (~19,000-11,000 years ago) represents the last major global climatological transition. In the Western United States, the LGM and deglacial were both characterized by increased effective moisture and expansive lake systems, with most lake growth and maximum lake extents achieved during the deglacial period. In stark contrast, the modern Great Basin is characterized by aridity and low effective moisture. The factors contributing to these large-scale changes in hydroclimates are critical to resolve, given this region is poised to undergo future anthropogenic-forced climate changes with large uncertainties in model simulations for the 21st century. Furthermore, there are ambiguous constraints on the magnitude and even the sign of changes in key hydroclimate variables between the LGM and present-day in both proxy reconstructions and climate model analyses of the Western United States.

In this work, I present new stable and clumped isotope data from several ancient lakes, analyze this new data in concert with previously published data, and compare both new and existing results to climate model simulations. Radiocarbon dated samples from ancient lakes constrain lake elevation and the timing of lake level fluctuations. Using a hydrological modeling framework, clumped isotope data constrain several other hydroclimate variables including temperature, precipitation rate, and evaporation rate, which are all used to assess climate model simulations of the same hydrological variables.

In Chapter 1, I compile new and existing radiocarbon ages from post-LGM lake basins, and provide an analysis of changing effective moisture through time and space. In Chapter 2, I provide a detailed analysis of our data from one specific basin, Lake Surprise, and provide evidence of evaporation depression as a key driver of lake growth. Finally, in Chapter 3, I use clumped and stable isotope analysis of samples collected across the Great Basin (by UCLA students and others) to provide evidence for spatial and temporal variation in hydroclimate. Concomitant analysis of proxy data and climate model simulations provides a robust means to understand past climate change, and by extension, predict how current hydroclimates may respond to expected future climate forcings.

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