UCLA

Lakes are responsive to climate, and in turn, sediment formed within lakes function as recorders of environmental change. This dissertation explores how the clumped and bulk stable isotope geochemistry of lacustrine sediments can be used to understand the terrestrial hydrologic cycle, both in the modern and past. To better understand the modern systematics of clumped isotopes in freshwater carbonates to extend to paleo-applications, Chapter 1 discusses the first extensive calibration study of different types of field-collected carbonates. We examine the uncertainties associated with the use of a single calibration in different types of carbonates, and evaluate relationships for material-specificity, allowing for more robust reconstructions of past temperature and water δ18O reconstructions. In the following three chapters, these calibrations are applied to late-Pleistocene lacustrine sediments from eleven lake basins in Western North America to evaluate multiple hydroclimate parameters, including temperature, water δ18O, evaporation, and precipitation, including for the Last Glacial Maximum (LGM; 23-19 ka) and deglaciation. In Chapter 2, we examine Lake Bonneville, which reached the size of a modern- day Great Lake at its maximum extent, and report the importance of evaporation suppression in setting and sustaining the lake, while also quantifying precipitation, with maxima during the early LGM and Heinrich Stadial 1 (HS1). In Chapter 3, we examine four basins in the Northern Great Basin to quantify the magnitude of evaporation and precipitation variation in the mid- latitudes, and test for a hypothesized precipitation dipole. At the two northernmost sites, we report evidence in support of enhanced evaporation depression and westerly-derived precipitation during the LGM and deglacial, leading to the presence of lakes in the region. We find at the southernmost site evidence for reduced evaporation and evidence for moisture advection into the continental interior from the south (e.g. higher atmospheric river and North American monsoonal precipitation) during the deglacial. In Chapter 4, we evaluate hydroclimatic changes using six basins in Arizona, New Mexico, and Northern Mexico, and find reduced temperatures and evaporation rates with increases in precipitation during the LGM and deglacial. The drivers of LGM and deglacial precipitation vary, with winter-derived precipitation the primary source of high levels of moisture in the Southwestern US, and tropical storms the likely origin of more modest enhancements in Northern Mexico.