Evidence for prolonged El Nino-like conditions in the Pacific during the Late Pleistocene: a 43 ka noble gas record from California groundwaters |
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| Authors: | J.T. Kulongoski D.R. Hilton J.A. Izbicki K. Belitz |
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| Affiliation: | 1. U.S. Geological Survey, California Water Science Center, San Diego, CA 92101, USA;2. Fluids and Volatiles Laboratory, Scripps Institution of Oceanography, UCSD, La Jolla, CA 92093-0244, USA;1. Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA;2. Department of Geosciences, University of Arizona, Tucson, AZ, USA;3. Department of Earth Sciences, University of Oxford, Oxford, UK;4. Lamont-Doherty Earth Observatory, Columbia University, New York, NY, USA;5. Department of Geology and Geophysics, University of Wyoming, Laramie, WY, USA;6. Department of Geosciences, University of Massachusetts Amherst, Amherst, MA, USA;7. Department of Earth Sciences, University of Minnesota, Minneapolis, MN, USA;8. Institute of Global Environmental Change, Xi''an Jiaotong University, Xi''an, China;1. California State University, Fullerton, Department of Geological Sciences, Fullerton, CA 92834, USA;2. University of Southern California, Department of Earth Sciences, Los Angeles, CA 90089, USA;1. Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10601, USA;2. California State University, Fullerton, Department of Geological Sciences, Fullerton, CA 92834, USA;1. University of Southern California, Department of Earth Sciences, 3651 Trousdale Pkwy, Los Angeles, CA 90089-0740, USA;2. Department of Geological Sciences, California State University, Fullerton, P.O. Box 6850, Fullerton, CA 92834-6850, USA;3. Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA |
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| Abstract: | Information on the ocean/atmosphere state over the period spanning the Last Glacial Maximum – from the Late Pleistocene to the Holocene – provides crucial constraints on the relationship between orbital forcing and global climate change. The Pacific Ocean is particularly important in this respect because of its dominant role in exporting heat and moisture from the tropics to higher latitudes. Through targeting groundwaters in the Mojave Desert, California, we show that noble gas derived temperatures in California averaged 4.2 ± 1.1 °C cooler in the Late Pleistocene (from ～43 to ～12 ka) compared to the Holocene (from ～10 to ～5 ka). Furthermore, the older groundwaters contain higher concentrations of excess air (entrained air bubbles) and have elevated oxygen-18/oxygen-16 ratios (δ18O) – indicators of vigorous aquifer recharge, and greater rainfall amounts and/or more intense precipitation events, respectively. Together, these paleoclimate indicators reveal that cooler and wetter conditions prevailed in the Mojave Desert from ～43 to ～12 ka. We suggest that during the Late Pleistocene, the Pacific ocean/atmosphere state was similar to present-day El Nino-like patterns, and was characterized by prolonged periods of weak trade winds, weak upwelling along the eastern Pacific margin, and increased precipitation in the southwestern U.S. |
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