HR: 1330h
AN: PP22A-1201    [PDF]
TI: A Holocene Sediment Record From Lake Elsinore, Southern California: Evidence for Relative Lake Level Change and the Onset of ENSO.
AU: * Kirby, M E
EM: mkirby@fullerton.edu
AF: Cal-State University, Fullerton, Dept. of Geological Sciences, Fullerton, CA 92834 United States
AU: Lund, S P
EM: slund@usc.edu
AF: University of Southern California, Dept. of Earth Sciences, Los Angeles, CA 90089 United States
AU: Poulsen, C J
EM: poulsen@umich.edu
AF: University of Michigan, Dept. of Geological Sciences, Ann Arbor, MI 48109 United States
AB: There are very few complete terrestrial, Holocene paleoclimate records from coastal southwestern North America. Lake Elsinore, located 120km southeast of Los Angeles, represents one of the only natural, non-playa lakes in the region. Furthermore, it is well documented that coastal southwestern North America is highly sensitive to changes in atmospheric circulation and its affect on regional hydrodynamics. As shown by Kirby et al. (in press), modern lake levels at Lake Elsinore respond directly to total annual precipitation, particularly winter season amounts. The lake is also located along the eastern Pacific Ocean where changes in ocean circulation and its thermal structure modulate the overlying atmosphere, and thus the adjacent continental climate. Here, we present two 7 meter sediment core records from Lake Elsinore spanning the entire Holocene. Although the cores are from the lake's littoral zone, they show surprisingly complete records with very little lithologic evidence for major hiatuses. A combination of sedimentological analyses (e.g., mass magnetic susceptibility (CHI); total percent carbonate; total organic matter) and lithologic descriptions provide insight to lake dynamics over the Holocene. Using the historical calibration between magnetic susceptibility and relative lake level (i.e., high lake levels = high CHI values and vice versa) from Kirby et al. (in press), we developed a first-order estimate of Holocene relative lake levels for Lake Elsinore. The historic calibration is extrapolated through the sediment record based on the assumption that, like today, first order lake level change is directly related to precipitation amount. Both total percent carbonate and total organic matter support our historical calibration between CHI and lake level. Our data suggest a relative increase in lake levels during the mid-Holocene (ca. 8,000 cal yr BP) and through to the present day. From this observation, we hypothesize that regional hydrology as linked to precipitation became more vigorous during the mid-Holocene (i.e., an increase in winter precipitation via an increase in the passage of winter cyclones). Because precipitation amount in coastal southwestern North America is so closely linked to ENSO variability, we further suggest that our observations support the hypothesis that modern ENSO variability and conditions developed during the mid-Holocene. This statement is in concert with recent findings from South America and the western Pacific that suggest a mid-Holocene onset of modern ENSO conditions. Our results are also supported by the recently published isotope data from Santa Barbara Basin (Friddell et al., 2003), which indicate an increase in more frequent "warm" ENSO events during the mid-Holocene. Our findings add to the growing number of terrestrial archives that document ENSO related Holocene variability and its timing of onset.
DE: 1512 Environmental magnetism
DE: 1610 Atmosphere (0315, 0325)
DE: 1620 Climate dynamics (3309)
DE: 1655 Water cycles (1836)
DE: 1833 Hydroclimatology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting