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N-alkanes as biomarkers for latest Pleistocene and Holocene precipitation in cores from Tulare Lake, CA, U.S.A.
With California suffering from one of the worst droughts on record, accurate models for paleohydrology are in high demand. Understanding the lake level histories of terminal lakes and their connection to Sierran runoff is an important step toward such models. Relative abundance and 𝛿13C measurements of n-alkanes extracted from Tulare Lake sediment cores are used to test previous interpretations of Holocene lake levels. Ratios of key n-alkanes are used to construct the Carbon Preference Index (CPI), Paq, and the C31 index. Both CPI and Paq values are in agreement with previously measured carbon/nitrogen data and indicate a mostly aquatic assemblage with small but steady input from terrestrial runoff over most of the last 20k years. The C31 index, combined with phytolith counts, shows a dominance of grass in the surrounding watershed during a time interval previously interpreted as containing high lake levels. 𝛿13C measurements reveal a strong depletion in 13C in this interval. Both the increase in grass abundance and depletion of 13C, particularly in the early Holocene, are taken as evidence of increasing precipitation.
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