Reconstructing climate variability and aridity in the Sierra Nevada, CA, based on isotopic evidence in sediments from Swamp Lake, Yosemite

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).An understanding of how climate in California responds to global and regional forcing mechanisms on multiple timescales is crucial for the management of scarce water resources and for predicting how natural patterns will interact with future climate warming. In light of the short instrumental record, only paleoclimatic records can provide the basis for understanding climate variability and ecosystem responses on longer timescales, capturing many cycles of the decadal and centennial-scale processes that control regional climate and determine water supplies, as well as the range of extreme conditions experienced under different climatic regimes.This grant develops new records of climatic variability in California based on isotopic evidence in the 19,000-year sedimentary sequence recovered from Swamp Lake in the central Sierra Nevada. This longer record allows high-resolution (20-50 yr) reconstructions for previously identified dry intervals in the mid- and late-Holocene, in order to better understand the decadal climate variability underlying long-term droughts. Previous work demonstrated that measurements of hydrogen isotopes (del-D) in biomarker compounds extracted from sedimentary organic matter (OM) provides a powerful paleohydrologic tool. The current project uses coupled del-D signatures of terrestrial plant and aquatic biomarkers to reconstruct past precipitation patterns, evaporative balance and water availability in the Sierra. A parallel record utilizing a suite of OM proxies (total C & N, C/N ratio, del-13C, del-15N, biomarker abundances) traces OM sources, lake productivity and other ecosystem responses to changing climate conditions. Climate reconstructions are supported by a multi-year field study to understand the isotope hydrology of the lake basin, calibration with the instrumental record, and comparisons with existing records from Swamp Lake, the Sierra Nevada, and California as a whole. The development of a decadally- to centennially-resolved record of Late Pleistocene-Holocene climatic variability for the Sierra Nevada represents a major step forward for paleoclimatic research in California. Such records are of direct societal importance because processes on these timescales determine water supplies, influence the distribution of plants and animals, and modulate the occurrence of higher-frequency events such as floods and droughts.The project provides involvement for underrepresented and minority undergraduate students in research, and participation in programs that aim to strengthen their leadership skills. Mentoring is coordinated for students from the AGEP program, and a 'first grad geology program - Geokids' at UCSC, and a K-12 education class 'Communicating ocean sciences' is offered. The project participates in the NSF-funded national education programs 'Science Diaries' and 'Kids Science Challenge' (through Pulse of the Planet, NPR). The PI also is developing an inquiry-based curriculum on the topic of paleoceangraphy and paleoclimatology.