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

来自圣巴巴拉盆地洋芯的古气候指标表明，在15-1.3万年前的晚更新世，加州南部发生了一次突然的气候变化，导致了海洋条件的快速变化和植被的景观尺度重组。该项目的目标是澄清这种快速植被变化的速度和时间，并确定驱动这种变化的具体气候参数。为了确定变化的速度，这项研究将从圣巴巴拉盆地的海洋岩芯中建立起15-13000年前的最低十年分辨率的花粉记录。来自圣巴巴拉盆地边缘圣克鲁斯岛的亚化石木材的稳定同位素比率与现代木材的稳定同位素比率的比较将被用来确定哪些气候参数发生了变化。初步分析确定，这些树木是不再生长在岛上的道格拉斯冷杉，这些树木是在圣巴巴拉盆地岩心记录的植被快速变化期间生长的。来自另外6个原木的样品将进行放射性碳年代测定，并将对年轮的氧和碳稳定同位素进行分析。为了确定是什么特定的气候参数驱动了加州沿海地区稳定同位素的变化，这项研究将把现代树木中的碳和氧稳定同位素比率与加州海岸沿线的气候参数联系起来。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。通过调查植被变化速度和气候参数的变化，本研究将阐明这种快速景观变化的原因。此外，这些结果将表明，更新世末期的气候变化是否与现代全球变暖类似。预计下个世纪气温、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，如南加州沿海地区。因此，本文试图构建的气候变化的精细尺度重建可以为政策制定者提供对南加州快速气候变化的长期视角。

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.