Paleoclimate proxies from an ocean core from Santa Barbara Basin indicate that there was an abrupt climate change in southern California in the late Pleistocene, 15-13 thousand years ago, that caused rapid changes in ocean conditions and a landscape scale reorganization of the vegetation. The goals of this project are to clarify the rate and timing of this rapid vegetation change and to determine the specific climate parameters that drove the shift. To determine the rate of change, this study will construct a pollen record with a minimum of bi-decadal resolution for the period of 15-13 thousand years ago from the ocean core from Santa Barbara Basin. Comparisons of stable isotope ratios from subfossil wood from Santa Cruz Island on the edge of the Santa Barbara Basin to the stable isotope ratios in modern wood will be used to determine what climate parameters changed. Preliminary analysis determined that the wood is Douglas fir, which no longer grows on the island, and that the trees grew during the period of rapid vegetation change recorded in the Santa Barbara Basin core. Samples from 6 more logs will be radiocarbon dated, and the oxygen and carbon stable isotopes from annual rings will be analyzed. To determine what specific climate parameters drive changes in stable isotopes in coastal California, this study will correlate carbon and oxygen stable isotope ratios in modern trees with climate parameters at sites along the coast of California. The stable isotope values from the subfossil wood will then be input into these correlations to determine the climate parameters when the trees were alive.
By investigating the rate of vegetation change and what climate parameters shifted, this study will clarify the causes of this rapid landscape transformation. In addition, these results will suggest if the climate change at end of the Pleistocene is an analog for modern global warming. Changes in temperature, sea level, and precipitation that are projected for the coming century may have dramatic impacts on arid urban areas such as coastal southern California. As a result, fine scale reconstructions of climate change such as those this dissertation seeks to construct can provide policy makers with a long-term perspective on rapid climate change in southern California.
