NOAA/WDS Paleoclimatology - Lower Bear Lake, California 9170 Year Multiproxy Sediment Data

STUDY NOTES: Multiproxy lake sediment data from Lower Bear Lake, California covering the last 9170 years. Parameters measured include magnetic susceptibility, LOI 550C, LOI 950C, ostracod counts, gastropod counts, and molar CN ratios. Lower Bear Lake was a small lake within Big Bear Valley prior to construction of Big Bear Dam in 1884 AD. Modern bathymetry reveals a distinct depression in the near-center of modern Big Bear Reservoir, representing the original Lower Bear Lake. A single drive, 4.5 m-long sediment core (BBLVC05-1) was extracted from Lower Bear Lake in 2005. The core was split, described, digitally photographed, and sub-sampled in the CSUF Paleoclimatology and Paleotsunami Laboratory. Mass magnetic susceptibility, LOI 550C (% total organic matter), and LOI 950C (% total carbonate) were determined at 1 cm contiguous intervals. Lower Bear Lake, California USA: 34.254°N, 116.914°W, 2059m elev
ABSTRACT SUPPLIED BY ORIGINATOR: A well-dated, 9170 calendar year before present (cal yr BP) paleohydrologic reconstruction is presented from Lower Bear Lake in the San Bernardino Mountains of the coastal southwest United States. This new multi-proxy record is characterized by alternating organic-rich/carbonate-rich sediment units, interpreted to reflect hydrologically-forced changes in the lake's depositional environment. Our interpretation of the proxy data indicates nine decadal-to-multi-centennial pluvial episodes (PE) over the past 9170 cal yr BP. Of these nine inferred pluvials, five are interpreted as more pronounced based on their combined proxy interpretations: (PE-V) 9170?-8250, (PE-IV) 7000-6400, (PE-III) 3350-3000, (PE-II) 850-700, and (PE-I) 500-476 (top of core) cal yr BP. The Lower Bear Lake record indicates that the San Bernardino Mountains, source region for the Mojave River and its terminal playa, was wet during the same periods (within dating errors), to several of the major pluvials proposed from the lakes in the sink of the Mojave River. Our comparison extends north also to Tulare Lake, which drains the south-central western Sierra Nevada Mountains. This temporally and spatially coherent signal indicates that a similar climate forcing acted to increase regional wetness at various times during the past 9170 cal yr BP. As originally proposed by Enzel, Ely, and colleagues (e.g., Enzel et al., 1989; Enzel, 1992; Ely et al., 1994; Enzel and Wells, 1997), we too contend that Holocene pluvial episodes are associated with changing the frequency of large winter storms that track across a broad region at decadal-to-multicentennial timescales. We build upon their hypothesis through the addition of new and better-dated site comparisons, recent advances in the understanding of atmospheric rivers, and improved knowledge of the ocean-atmosphere dynamics that caused the early 20th century western United States pluvial.