n-Alkane biomarker distributions in sediments from Swamp Lake (SL), in the central Sierra Nevada of California (USA), provide evidence for an increase in mean lake level ~3000yr ago, in conjunction with widespread climatic change inferred from marine and continental records in the eastern North Pacific region. Length distributions of n-alkane chains in modern plants growing at SL were determined and compared to sedimentary distributions in a core spanning the last 13ka. As a group, submerged and floating aquatic plants contained high proportions of short chain lengths (<nC25) compared to emergent, riparian and upland terrestrial species, for which chain lengths >nC27 were dominant. Changes in the sedimentary n-alkane distribution over time were driven by variable inputs from plant sources in response to changing lake level, sedimentation and plant community composition. A shift toward shorter chain lengths (nC21, nC23) occurred between 3.1 and 2.9ka and is best explained by an increase in the abundance of aquatic plants and the availability of shallow-water habitat in response to rising lake level. The late Holocene expansion of SL following a dry mid-Holocene is consistent with previous evidence for increased effective moisture and the onset of wetter conditions in the Sierra Nevada between 4.0 and 3.0ka.
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Reviews from Megan Young, Steven Silva, Ken Adams, and two anonymous reviewers improved the quality of the paper. We thank John Barron, Daniel Boone, Jordon Bright, Dan Cayan, Pamela Campbell, Alison Colwell, Douglas Hallett, Angela Lam, Ian McKenna, Cara Meeker, Scott Starratt, Alex Sessions, Susan Smith, Jan van Wagtendonk and Anne Walton for their assistance at various points in this project. This research was supported by grants from the National Science Foundation ( EAR-0902218 to A.P.; ATM-9521610 to R.S.A.), the Yosemite Fund (R.S.A.), funding from the USGS , and graduate student fellowships from Stanford University and the Calfed Bay-Delta Science Program (to J.S.). NAU Laboratory of Paleoecology Contribution #142.
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- Lake level
- Plant n-alkanes
- Sierra Nevada