Stable isotope evidence for a foggy climate on Santa Cruz Island, California at ~ 16,600 cal. yr. B.P.

In this study we use stable isotope analysis to investigate the climate in southern coastal California during the last 10,000 years of the Pleistocene by comparing the carbon and oxygen stable isotope ratios of preserved Douglas-fir (Pseudotsuga menziesii) wood from Santa Cruz Island to modern Douglas-fir wood from northern California. AMS age determination indicates that the preserved trees grew at about 16,600 ± 270 cal. yr. B.P. After isolating cellulose from both the modern and Pleistocene wood to remove any potential bias due to differential decomposition rates of wood components [Loader, N.J., Robertson, I., McCarroll, D., 2003. Comparison of stable carbon isotope ratios in whole wood, cellulose, and lignin of oak tree-rings. Palaeogeography, Palaeoclimatology, Palaeoecology 196, 395–407.], we find that the Pleistocene Douglas-fir wood has significantly greater carbon isotope discrimination and significantly more enriched δ18O than the modern Douglas-fir wood, which suggests that the Douglas-fir trees growing on Santa Cruz Island at ~ 16,600 cal. yr. B.P. experienced less moisture stress and used more enriched water from fog than Douglas-fir trees at Point Reyes today.