An organic geochemical record of Sierra Nevada climate since the LGM from Swamp Lake, Yosemite
نویسندگان
چکیده
Sediment records from Swamp Lake (SL) in the central Sierra Nevada, California, provide evidence of climatic change on millennial and centennial timescales over the lastw20,000 years. Total organic carbon (TOC) abundancevaried in concertwith elemental and isotopic tracers of organicmatter (C/N, dCorg, d15N), 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 (w19.7e10.8 cal. kyr BP) was dominated by fluctuations between relatively warm/dry intervals with high TOC (17.4e16.5, 15.8e15.0, 13.9e13.2, 11.4e11.0 cal. kyr BP) and cold/wet intervals (16.5e15.8, 14.8e13.9, 13.1e11.6, 11.0e10.7 cal. kyr BP) characterized by low TOC and high detrital input. The Holocene (w10.7 cal. kyr BPe present)was characterized by three abrupt increases in TOC (after w10.8, 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 changingwinter 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 pastw20,000 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. ! 2012 Elsevier Ltd. All rights reserved.
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