Geological Society of America

T135 Cenozoic Lakes Across Western North America – from the Varved Beds of the Green River Formation to the Ice-Covered Alpine Lakes of the Sierra Nevada

Monday, 23 September 2024
1:30 PM - 5:30 PM
213B

TWENTIETH CENTURY EXTREME PRECIPITATION DETECTED IN A HIGH-RESOLUTION, COASTAL LAKE SEDIMENT RECORD FROM CALIFORNIA

Paper number: T135-3
Program: Technical Sessions
Time: 1:55 PM – 2:15 PM

Authors

Clarke Knight Presenting Author
Mountain View, CA
Scott Starratt
Geology, Minerals, Energy, and Geophysics Science Center, Menlo Park, CA
David Wahl
University of California, Berkeley, Berkeley, CA
David Wahl
U.S. Geological Survey, Moffett Field, CA
Jason Addison
Geology, Minerals, Energy, and Geophysics Science Center, Menlo Park, CA
Mark Baskaran
Wayne State University, Detroit, MI
R. Scott Anderson
Northern Arizona University, Flagstaff, AZ
Marie Champagne
Geology, Minerals, Energy, and Geophysics Science Center, Moffett Field, CA
Lysanna Anderson
U.S. Geological Survey, Reston, CA
Liubov Presnetsova
Geology, Minerals, Energy, and Geophysics Science Center, Menlo Park, CA
Beth Caissie
Oregon State University, Corvallis, OR

Abstract

California faces increasing economic and societal risks from extreme precipitation and flooding associated with atmospheric rivers (ARs) under projected twenty-first century climate warming. Lake sediments can retain signals of past extreme precipitation events, allowing reconstructions beyond the period of instrumental records. Here, we provide a pre-instrumental record of AR-related extreme precipitation from the last century using a natural archive of lake sediments. Our site – Wildcat Lake, Point Reyes National Seashore – is in the latitudinal zone of the highest frequency landfall for modern ARs in California. First, we cored Wildcat Lake in 2021 and estimated the sediment ages using a Bayesian-based ²¹⁰Pb, ¹³⁷Cs, and ²²⁶Ra model (± 4 years in the calibration period) and obtained high-resolution imagery, elemental data from XRF, and grain size data to identify detrital layers in the sediment core. Excursions in erosional proxy data (Ti/Al) are positively and significantly correlated (rmedian = 0.45, pmedian = 0.04) with modern records of integrated vapor transport (kg m-1 s-1), a key metric of AR intensity, using correlations that incorporate age model uncertainty. Signals of extreme precipitation – Ti/Al and K/Al excursions – coincide with every extreme AR year (n=23) that occurred since CE 1948. Water years with short or less intense ARs were not captured by this record, suggesting a site-specific threshold for energetic sediment delivery to the core site or the efficiency of the sediment runoff from nearby slopes. Despite the land-use change near the study site, the data suggest intense and long-lasting AR storms are identifiable in this sedimentary record. These results demonstrate the potential of lacustrine archives to provide records of extreme AR activity and provide context for modern variability in AR frequency and magnitude.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-401970

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