We employed a new, multi-proxy record from Baldwin Lake (∼125–10 ka) to examine drivers of terrestrial Southern California climate over long timescales. Correlated bulk organic and biogenic silica proxy data demonstrated high-amplitude changes from 125 to 71 ka, suggesting that summer insolation directly influenced lake productivity during MIS 5. From 60 to 57 ka, hydrologic state changes and events occurred in California and the U.S. Southwest, though the pattern of response varied geographically. Intermediate, less variable levels of winter and summer insolation followed during MIS 3 (57–29 ka), which likely maintained moist conditions in Southern California that were punctuated with smaller-order, millennial-scale events. These Dansgaard-Oeschger events brought enhanced surface temperatures (SSTs) to the eastern Pacific margin, and aridity to sensitive terrestrial sites in the Southwest and Southern California. Low temperatures and reduced evaporation are widespread during MIS 2, though there is increasing evidence for moisture extremes in Southern California from 29 to 20 ka. Our record shows that both orbital-scale radiative forcing and rapid North Atlantic temperature perturbations were likely influences on Southern California climate prior to the last glacial. However, these forcings produced a hydroclimatic response throughout California and the U.S. Southwest that was geographically complex. This work highlights that it is especially urgent to improve our understanding of the response to rapid climatic change in these regions. Enhanced temperature and aridity are projected for the rest of the 21st century, which will place stress on water resources.
Bibliographical noteFunding Information:
We are grateful for the financial support provided by the UCLA Institute of the Environment and Sustainability Presidential Fund, UCLA Graduate Division, Limnological Research Center, Geological Society of America, UCLA Dept. of Geography John Muir Memorial Endowment, Society of Woman Geographers, and the Department of the Interior Southwest Climate Science Center. Fieldwork and core recovery were greatly assisted by Katie Nelson, Scott Eliason, and Gina Griffith of the San Bernardino National Forest; Larry Winslow of Big Bear, CA; and Gregg Drilling, L.L.C. KCG especially thanks Wendy Barrera for leading IRSL subsampling and preparation at the UCLA Luminescence Laboratory, assistance from Jessica Rodysill and Kristina Brady while visiting the Limnological Research Center at the University of Minnesota, and Katherine Whitacre at Northern Arizona University's Amino Acid Geochronology Lab. We thank several students for their assistance in the field and lab, including Lauren Brown, April Chaney, Elaine Chang, Christine Hiner, Tamryn Kong, Alec Lautanen, Jennifer Leidelmeijer, Setareh Nejat, Alex Pakalniskis, Sargam Saraf, Nicole Tachiki, Marcus Thomson, Alice Wong, Alex Woodward and Ren?e Yun. The thorough and thoughtful comments of two anonymous reviewers greatly improved the paper, and are much appreciated. Candid conversation and feedback from many of the investigators cited, too numerous to name here, have also improved our discussion of long-term climate change in the North American West.
Copyright 2017 Elsevier B.V., All rights reserved.
- Dansgaard-Oeschger events
- Last glacial maximum
- Marine isotope stages
- Orbital forcing
- San Bernardino Mountains
- Southern California
- Summer insolation
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