A Speleothem Record of Great Basin Paleoclimate: The Leviathan Chronology, Nevada

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Speleothem studies from vadose-zone caves in the Great Basin have provided insight into the timing and controls of climatic change over the last 175,000 years. These studies integrate stable oxygen, carbon, and trace-element data to infer past temperature and wetness in the Great Basin, yielding new insights into the controls and timing on climate change on timescales ranging from centuries to orbital scales. This manuscript summarizes some of these records, with a focus on a long orbital-scale, oxygen-isotope reconstruction from Nevada called the Leviathan chronology, newly extended to 208,000 yr B2K (before year 2000). This speleothem-paleoclimate reconstruction is comprised of samples collected from Leviathan, Pinnacle, and Lehman Caves, Nevada, and shows orbital-scale variations in stable oxygen isotopes (δ18O) that closely follow the variations in Milankovitch-controlled summer insolation in the northern hemisphere. The data show that glacial-interglacial terminations arrive “on-time” as expected from Milankovitch variations, and that their duration was set by insolation. The strong match between Great Basin δ18O values and insolation is also evident in minimum (cold) δ18O values during marine isotope stages (MIS) 5d and 7, when insolation was low despite minimal ice volume. Holocene climate variation followed the orbital insolation trend, and agrees with Antevs’ formulation of a distinct altithermal interval in the Great Basin. Surprisingly, the timing of δ18O variations in the Leviathan chronology is markedly different to those originally published from Devils Hole, Nevada, suggesting that the phreatic origin of Devils Hole calcite may impart a nonclimatic forcing on calcite δ18O values. This observation is confirmed by new Devils Hole cores that generally support the discoveries enabled by the Leviathan chronology, but which show a delayed and dampened δ18O signal arising from dispersion in the regional carbonate aquifer. © 2016 Elsevier B.V.