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

来自圣巴巴拉盆地海洋岩心的古气候代用物表明，在更新世晚期（15-13万年前），南加州发生了一次突变气候变化，导致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，并确定推动这种变化的具体气候参数。为了确定变化的速度，本研究将从圣巴巴拉盆地的海洋核中建立一个15- 1.3万年前的花粉记录，其分辨率最低为双年代际。将圣巴巴拉盆地边缘圣克鲁斯岛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进行比较，将用于确定气候参数发生了哪些变化。初步分析确定，这些木材是道格拉斯冷杉，这种树木已不再生长在岛上，而且这些树木生长在圣巴巴拉盆地中心记录的快速植被变化时期。另外6个原木的样本将进行放射性碳测年，并分析来自年轮的氧和碳稳定同位素。为了确定是什么特定的气候参数驱动了加利福尼亚沿海地区稳定同位素的变化，本研究将把现代树木的碳和氧稳定同位素比率与加利福尼亚沿海地区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，以确定树木活着时的气候参数。通过调查植被变化的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，这些结果将提示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、海平面和降水的变化可能会对南加州沿海等干旱城市地区产生巨大影响。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.