The Trans-Sierra Climatic Contrast

更新世末期关键千年期间北美西南部气候和环境反应的区域格局以及该区域格局与全球气候变化的关系仍然是国家和国际上重要的研究专题。加利福尼亚州东部的内华达山脉是今天主要的气候和植被边界，但在上一个冰河时代结束时，大盆地般的植被覆盖在内华达山脉南部两侧的较低山坡上。在这个项目中，研究人员将收集、测定和检查加利福尼亚州东部塞拉峰以西的四个湖泊的湖芯年代学，以评估两种相互矛盾的假说，这两种假说解释了为什么西塞拉山脉在上一次冰期结束时更干燥，而东塞拉山脉更潮湿。第一种假设认为，季风活动增强是由于夏季日照增加和海陆热力对比增强所致。第二种选择通过冬季急流的南移解释了北方的干旱和南方的潮湿。这项研究将阐明我们对干旱的北美晚第四纪植被历史以及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以及区域变化与全球变化之间关系的理解。

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.