Hydrologic variability and the onset of modern El Niño–Southern Oscillation: a 19 250‐year record from Lake Elsinore, southern California

Abstract

AbstractThere are very few terrestrial palaeoclimate archives spanning the Last Glacial Maximum through the Holocene from coastal southern California. Yet, knowledge of past climate dynamics is critical for assessing present and future constraints on the region's dwindling freshwater resources. We present initial results from two drill cores extracted from the present‐day edge of Lake Elsinore, southern California's largest natural lake. Using a multiproxy approach including lithologic description, mass magnetic susceptibility, LOI 550°C (total organic matter), and LOI 950°C (total carbonate), we infer first‐order, long‐term climate change over the past 19 250 calendar years. Furthermore, we suggest possible first‐order forcing mechanisms that drive this change, which include presence/absence of continental ice sheets, insolation, and complex ocean–atmosphere interactions. Our results indicate four distinct millennial‐scale climate modes over the past 19 250 calendar years. These modes include a wet Last Glacial Maximum (19 250–17 120 cal. yr BP), a relatively dry late‐Glacial/Holocene transition (17 120–9450 cal. yr BP), a wet early Holocene (9450–7670 cal. yr BP), and a highly variable mid‐to‐late Holocene climate (i.e., alternating wet/dry cycles; 7670 cal. yr BP–present). We attribute the mid‐to‐late Holocene climate interval to the onset of El Niño–Southern Oscillation ca. 7000 cal. yr BP and a more vigorous hydrologic system. These results are supported by a variety of regional terrestrial and marine palaeoclimate archives. Copyright © 2005 John Wiley & Sons, Ltd.