The Trans-Sierra Climatic Contrast

更新世末期关键千年北美西南部气候与环境响应的区域格局及其与全球气候变化的关系一直是国内外重要的研究课题。今天，加州东部的内华达山脉是一个主要的气候和植被边界，但在最后一个冰河时代结束时，内华达山脉南部两侧较低的斜坡上覆盖着类似大盆地的植被。在这个项目中，研究者将收集、确定日期并检查加州东部塞拉峰以西的四个湖泊的湖芯年表，以评估两种相互竞争的假设，这两种假设解释了为什么西塞拉在最后一个冰期结束时更干燥，而东塞拉更湿润。第一种假说认为，季风活动的增强是由于夏季日晒量的增加和海陆热对比的增强。第二种解释是冬季急流向南移动来解释北方干旱和南方潮湿。该研究将阐明我们对干旱的北美晚第四纪植被史和影响它的气候模式的理解。这些知识将增加我们对气候和植被变化过程的理解，以及区域变化与全球变化的关系。

Regional patterns of climate and environmental response in southwestern North America during the pivotal millennia of the end of the Pleistocene epoch, and the relations of that regional pattern to global climate change continue to be nationally and internationally important research topics. The Sierra Nevadas of eastern California are a major climatic and vegetational boundary today, but at the end of the last ice age Great Basin-like vegetation coverered lower slopes on both sides of the southern Sierra Nevada. In this project, the investigator will collect, date, and examine lake-core chronologies from four lakes west of the Sierra crest in eastern Calfornia in order to evaluate two competing hypotheses that explain why the western Sierra was drier and the eastern Sierra was wetter at the end of the last glacial period. The first hypothesis argues that enhanced monsoonal activity was due to greater summer insolation and an enhanced land-sea thermal contrast. The second alternative explains the northern aridity and the southern moistness by a southward displacement of the winter jet stream. The study will illuminate our understanding of the late Quaternary vegetation history of arid North America and the climatic patterns that have influenced it. This knowledge will increase our understanding of processes of climatic and vegetation change and the ways the regional changes relate to global changes.