G.K. Gilbert’s 1890 monograph on Lake Bonneville published by the United States Geological Survey initiated over a century of research on Quaternary lakes in the American west. The continuation of this work is increasingly pertinent today with the need to test climate models used to forecast future water resources in the region as the climate warms. Importantly the presence or absence of lakes in terminal basins provide an unequivocal measure of wetness. In this work I will show that wetter conditions during both colder- and warmer-than-present periods in the past are recorded in shoreline and outcrop data from the latest Pleistocene and the middle-Pliocene. In conjunction with paleotemperature data, derived from pollen, macrofossil assemblages and carbonate clumped isotope measurements, I will show scaling relationships implying that: 1) Pleistocene lakes during glacial maxima in the northern Great Basin do not require substantial precipitation increases to explain lake shoreline extents; and 2) middle-Pliocene lakes would have required up to a doubling of precipitation in the southwest. These inferences provide quantitative targets for assessing the performance of climate model simulations of the terrestrial water cycle. In addition, I will show ongoing work associated with the application of carbonate clumped isotope thermometry and triple oxygen isotope measurement to lacustrine lake sediments in the western United States.
Speaker: Daniel Ibarra, UC Berkeley
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