Fluctuation in leaf wax D/H ratio from a southern California lake records significant variability in isotopes in precipitation during the late Holocene

The hydrogenisotopic composition of plant molecular markers in modern vegetation and marine sediments in southern California have been intensively studied. Here we report a late Holocene reconstruction from Zaca Lake in coastal southern California, together with modern hydrological and vegetation studies in the catchment. The small catchment and decadal sampling resolution throughout the 9 m, 3000 yr sedimentary record provided a high resolution terrigenous counterpart of nearby marine records from the Santa Barbara Basin. Today, delta D values of precipitation average -51.5 parts per thousand +/- 18 (1 sigma, n = 7). Modern plant leaf wax delta D values for the C-28 n-alkanoic acid averaged -141 parts per thousand +/- 11(1 sigma, n = 10) for Quercus agrifolia, with a calculated fractionation relative to precipitation (epsilon(wax/precip)) of -94 parts per thousand +/- 22(1 sigma, n = 10); in contrast, therewas negligible production of the C-28 acid by co-dominant Pinus coulteri. Downcore, the C-28 acid delta D values ranged between -101 parts per thousand and -177 parts per thousand (mean -150 parts per thousand +/- 8, 1 sigma, n = 490). Abundance distributions suggested that the sedimentary C-28 acid was dominated by Quercus, implying that paleoprecipitation varied between extremes of -8 parts per thousand and -92 parts per thousand (mean -63 parts per thousand +/- 14, compound 1 sigma, n = 490). The 3000 yr leaf wax D/H record from Zaca Lake revealed substantial temporal variability, greater than observed in a speleothem reconstruction of similar resolution. We suggest that the plant-based proxy may magnify the variability by sampling spring precipitation preferentially. Centennial-duration positive isotopic excursions were associated with more sub-tropical moisture sources and drier conditions including during the Medieval Climatic Anomaly, and negative excursions were associated with N Pacific sources and wetter conditions including during the Little Ice Age. (C) 2013 Elsevier Ltd. All rights reserved.