Masters Thesis

Possible millennial-scale climate cycles and their effect on Tulare Lake, CA during the Late Pleistocene

Tulare Lake level predominantly fluctuates due to varying amounts of runoff from the Sierra Nevada as a result of changes in regional climate. It is important to constrain the details of such change because they allow us to capture the range of natural hydrologic variability for the San Joaquin Valley. This study attempts to extend this record back into the late Pleistocene beyond the past 25 ka reported in previous works. A multi-proxy approach is used including: % total inorganic carbon, % total organic carbon, % nitrogen, CN ratios, granulometry, and magnetic susceptibility. Resulting clay percentages are affected by increases or decreases in Sierran runoff, while low TOC, N, CN, and TIC values throughout the core suggest that Tulare lake was unproductive, sterile, and fresh from resulting glacial stream runoff. Fluctuations in clay % versus depth are found to have similar morphology to the Dansgaard-Oeschgard (D-O) oscillations found in North Atlantic region marine ice cores, wherein increases in clay % correspond with interstadials (warm/deeper lake conditions) and decreases with stadials (cold/lower lake conditions). Samples analyzed from core drives 7-10 of the Tulare Lake TL054A core did not result in sufficient 14C for dating. Instead, ages were extrapolated using data from higher in the core. Also, an alternative age model for the sediments of this study was hypothesis-based on the presumed correlation of lake-level with climate conditions associated with the well dated GICC05 Greenland ice core record. The latter hypothesis suggests an age range of 25,000-35,000 cal yr BP and thus predicts the presence of the Mono Lake Excursion (MLE) in the TL05-4A core.

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