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n-Alkane evidence for the onset of wetter conditions in the Sierra Nevada, California (USA) at the mid-late Holocene transition, ~3.0ka

Street, Joseph H., Anderson, R. Scott, Rosenbauer, Robert J., Paytan, Adina
Quaternary research 2013 v.79 no.1 pp. 14-23
alkanes, aquatic plants, biomarkers, botanical composition, climate change, habitats, lakes, sediments, swamps, California, Sierra Nevada (California)
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.