Doctoral Dissertation Research: High Resolution Reconstruction of Late Pleistocene Climate Change in Southern California

圣巴巴拉盆地海洋岩芯的古气候代用指标表明，在15-13万年前的晚更新世，加州南部发生了一次气候突变，导致了海洋环境的急剧变化和植被景观尺度的重组。 该项目的目标是澄清这种快速植被变化的速度和时间，并确定推动这种转变的具体气候参数。 为了确定变化率，本研究将从圣巴巴拉盆地的海洋岩芯中建立一个1.5 - 1.3万年前的花粉记录，其分辨率至少为20年。 来自圣巴巴拉盆地边缘的圣克鲁斯岛的亚化石木材的稳定同位素比与现代木材的稳定同位素比的比较将用于确定气候参数的变化。 初步分析确定，木材是道格拉斯冷杉，这不再生长在岛上，树木生长在快速植被变化期间记录在圣巴巴拉盆地核心。 将对另外6根原木的样品进行放射性碳年代测定，并分析年轮中的氧和碳稳定同位素。 为了确定哪些具体的气候参数驱动稳定同位素在沿海加州的变化，这项研究将相关的碳和氧稳定同位素比率在现代树木与气候参数沿着加州沿海的网站。 然后将亚化石木材的稳定同位素值输入到这些相关性中，以确定树木存活时的气候参数，通过调查植被变化的速率和气候参数的变化，本研究将阐明这种快速景观转变的原因。 此外，这些结果将提示更新世末的气候变化是否是现代全球变暖的一种模拟。 预计未来世纪的气温、海平面和降水量的变化可能会对干旱的城市地区产生巨大影响，如加州南部沿海地区。 因此，气候变化的精细尺度重建，如本论文试图构建可以提供政策制定者在南加州的快速气候变化的长期前景。

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.