HR: 0800h
AN: PP11A-0220    [Abstracts]
TI: Paleoenvironmental Reconstruction of a Glacial-age Sediment Core From Baldwin Lake, Southern California: Evidence for Multi-timescale Climate Variability
AU: * Blazevic, M A
EM: mablazevic@gmail.com
AF: California State Univeristy, Fullerton, Department of Geological Sciences, 800 N. State College Blvd., Fullerton, CA 92831, United States
AU: Kirby, M E
EM: mkirby@fullerton.edu
AF: California State Univeristy, Fullerton, Department of Geological Sciences, 800 N. State College Blvd., Fullerton, CA 92831, United States
AU: Browne, B L
EM: bbrowne@fullerton.edu
AF: California State Univeristy, Fullerton, Department of Geological Sciences, 800 N. State College Blvd., Fullerton, CA 92831, United States
AU: Woods, A D
EM: awoods@fullerton.edu
AF: California State Univeristy, Fullerton, Department of Geological Sciences, 800 N. State College Blvd., Fullerton, CA 92831, United States
AU: Bowman, D D
EM: dbowman@fullerton.edu
AF: California State Univeristy, Fullerton, Department of Geological Sciences, 800 N. State College Blvd., Fullerton, CA 92831, United States
AB: A detailed multi-proxy sedimentological and high-resolution thin-section image analysis was conducted on a glacial-age (20,000-65,000 calendar years BP) 14-meter sediment core from Baldwin Lake, Southern California. The results are used to investigate the difference in depositional environment and process between the core's two predominant sediment units: massive versus laminated/semi-laminated sediments. Massive sediments produce typically high magnetic susceptibility, low total organic matter, and high mean grain-size values. An analysis of thin-sections from the massive sediments reveal a heterogeneous sediment fabric lacking any distinct structures. Laminated and semi-laminated sediments produce generally low magnetic susceptibility, high total organic matter, and low mean-grain-size values. Thin-sections from laminated sediments reveal very diffuse cm-scale laminae couplets of alternating light and dark layers. There are, however, two laminated sections, which deviate from the latter characterization. These two "anomalous" sections contain highly variable magnetic susceptibility, low total organic matter, and variable mean grain-size values. Based on the data above, four lacustrine facies are proposed: (L1) organic-poor, massive, medium-to coarse-silts with high magnetic susceptibility represent deposition in a playa lake environment; (L2) organic-rich, massive and semi-laminated, fine-to medium-silts with high magnetic susceptibility represent deposition in a shallow lake with highly variable lake levels; (L3) organic-poor, semi-laminated to laminated, fine-to coarse-silts with highly variable magnetic susceptibility represent a persistent shallow lake environment; and, (L4) organic-rich, semi-laminated to laminated fine-to medium silts with low magnetic susceptibility represent deposition in a deep lake environment. At the facies scale, the lake's hydrologic state appears related to hemispheric climate patterns based on a comparison to the GISP2 oxygen isotope record. To investigate the finer-scale (sub-centennial) variability, a gray- scale digital image analysis of the sediment thin-sections was pursued assuming a constant sedimentation age model between dates. The image analysis shows a high degree of variability within both massive and laminated sediments. Wavelet analysis and wavelet spectrum of the gray-scale data in the massive, semi-laminated, and laminated sediments reveal a fairly dominant multi-decadal scale signal (10-100 yrs). A weaker sub-decadal signal (2-7 yrs) is present for all sediment types, but only the laminated sediments show this sub-decadal signal consistently. Temporal variability in the wavelet spectrum for the massive and some laminated sediments argues for a non-stationary climate regime during the last glacial period. Tentatively, we assign sub-decadal variability to ENSO. The dominant multi-decadal scale signals may be linked to complex ocean-atmosphere dynamics such as the PDO and AMO. These results suggest that both ENSO and the PDO influenced glacial climate in Southern California. However, our data also suggest that these systems were non-stationary through time.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting