Sediment records from Swamp Lake (SL) in the central Sierra Nevada, California, provide evidence of climatic change on millennial and centennial timescales over the last ∼20,000 years. Total organic carbon (TOC) abundance varied in concert with elemental and isotopic tracers of organic matter (C/N, δ 13C org, δ 15N), biogenic silica content, total magnetic susceptibility, and sediment lithology. We interpret the down-core proxy records as representing the response of the lake environment, in terms of temperature, seasonal ice cover, mixing regimes, runoff and in situ OM and nutrient cycling, to shifting climate states. These environmental factors in turn drove changes in algal productivity, OM sources, microbial OM regeneration and secondary production, and detrital input. The late Pleistocene (∼19.7-10.8 cal. kyr BP) was dominated by fluctuations between relatively warm/dry intervals with high TOC (17.4-16.5, 15.8-15.0, 13.9-13.2, 11.4-11.0 cal. kyr BP) and cold/wet intervals (16.5-15.8, 14.8-13.9, 13.1-11.6, 11.0-10.7 cal. kyr BP) characterized by low TOC and high detrital input. The Holocene (∼10.7 cal. kyr BP - present) was characterized by three abrupt increases in TOC (after ∼10.8, 8.0, and 3.0 cal. kyr BP) and numerous century-scale fluctuations. TOC increases reflected enhanced lake productivity and OM recycling, and reduced detrital input, in response to changing winter temperature and hydrologic regimes. Inferred environmental changes at SL correlate with other Sierra Nevada paleorecords, and with reconstructed sea surface temperatures along the California margin. Parallel changes in the SL and SST records over the past ∼20,000 years provide new evidence that continental climate in the Sierra Nevada and the California Current system have responded, on multiple timescales, to common drivers in North Pacific ocean-atmospheric circulation.
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Three anonymous referees contributed reviews that improved the quality of the paper. Scott Starratt, Douglas Hallett and John Barron also provided helpful comments at various points in this project. We thank Jan van Wagtendonk, Dan Cayan, John Barron and James Stringfellow for logistical assistance; Daniel Boone, Jordon Bright, Alison Colwell, Elizabeth Derse, Douglas Hallett, Justin Holl, Erin Hult, Karen Knee, Tim Lambert, Jackie Liu, Ian McKenna, Nadine Quintana-Krupinski, Lydia Roach, and Benjamin Saenz for field assistance; and Cara Meeker and Susan Smith for laboratory assistance. Initial core characterization was carried out at LacCore (National Lacustrine Core Facility), Department of Geology and Geophysics, University of Minnesota. Biogenic silica measurements were made by Jordon Bright in the Sedimentary Records of Environmental Change laboratory at NAU. This research was supported by grants from the National Science Foundation ( EAR-0902218 ) (A.P.), Calfed Bay-Delta Science Program (J.S.), and The Yosemite Fund (R.S.A.), and by funding from the U.S. Geological Survey . J.S. was supported by graduate student fellowships from Stanford University and the Calfed Bay-Delta Science Program. Laboratory of Paleoecology Contribution # 132.
Copyright 2012 Elsevier B.V., All rights reserved.
- Sedimentary organic matter
- Sierra Nevada, California
- Stable isotopes