Developing a Record of Quaternary Climatic Oscillation for the Eastern Sahara through Analysis of Fossil-spring Tufas and Lacustrine Deposits, Western Desert, Egypt

该赠款开发了东撒哈拉第四纪的气候年表，并通过对目前极端干旱的埃及西部沙漠中的化石泉和湖泊沉积物的调查，绘图和分析来限制撒哈拉潮湿环境的条件。春季碳酸盐岩，或凝灰岩，可通过铀系和电子自旋共振技术确定年代，并直接记录北非降水增加的时间。这些潮湿阶段的环境条件重建通过稳定同位素地球化学的凝灰岩，湖相碳酸盐岩，腹足类壳文石，以及其他代理。利用湖泊沉积物的测量和地球化学分析资料，建立了湖泊水化学演化的水文和同位素平衡模型。这些模型产生了对多雨期湖泊寿命期间气候变化的定量估计。由此获得的数据被用来检验这样一个假设，即撒哈拉多雨期出现的频率高于间冰期最高值，这是对非洲季风中基于轨道岁差和湿度的波动的一种反应，建立东撒哈拉精确、详细的气候年表可以与区域气候记录进行详细比较（地中海和大西洋核心，东非裂谷湖核心），这有助于拼凑气候联系。U系列日期的预测精度还允许与轨道参数进行直接比较，以检验北非产生降雨的基于太阳辐射的机制，或查明该区域的非轨道气候波动。通过研究获得的气候历史还可以用来测试关于北非大陆在第四纪全球碳和甲烷预算中的作用的假设。像撒哈拉这样大面积地区的“绿化”，以及整个撒哈拉大面积湖泊的形成，将对气候系统产生重大的反馈。最后，更好地了解北非多雨期的频率和强度，将有助于重新评估撒哈拉在第四纪期间对现代人类从非洲向外扩散的障碍程度，人类起源研究的一个重要问题。拟议工作的更广泛影响包括通过举办一个简短的达赫莱绿洲第四纪地质学和地貌学实地技术课程。这项工作是攻读博士学位的基础。一个私家侦探的女研究生气候年表存放在基于网络的世界古气候数据中心数据库中，以便广泛使用。在野外工作中收集的样品成为古环境重建课程的一部分。

This grant develops a climate chronology for the Quaternary of the Eastern Sahara and to constrain the conditions of humid-phase environments in the Sahara via survey, mapping, and analysis of fossil-spring and lacustrine deposits in the currently hyperarid Western Desert of Egypt. The spring carbonates, or tufas, are datable by Uranium-series and Electron Spin Resonance techniques, and directly record times of increased precipitation in North Africa. The environmental conditions of these humid phases are reconstructed via the stable-isotope geochemistry of tufas, lacustrine carbonates, and gastropod-shell aragonite, among other proxies. Data from survey and geochemical analyses of lacustrine sediments are used to build hydrologic- and isotopic- balance models of lacustrine hydrochemical evolution. These models generate quantitative estimates of climatic variability during the lifespan of the pluvial -phase lakes. Data thus obtained is used to test the hypothesis that Saharan pluvial phases have occurred more frequently than interglacial maxima, as a response to orbital precession- and obliquity-based fluctuations in the African Monsoon.The establishment of a precise, detailed climate chronology for the Eastern Sahara allows for detailed comparison with regional climate records (Mediterranean and Atlantic cores, East African Rift Valley lake cores), which aids in piecing together climate linkages. The projected precision of the U-series dates also permits direct comparison with orbital parameters, in order to test insolation-based mechanisms for generating rainfall in North Africa, or to identify non-orbital climatic fluctuations in the region. The climatic history obtained by the research could additionally be used to test hypotheses regarding the role of the North African landmass in global carbon and methane budgets over the course of the Quaternary. The 'greening' of such a substantial area as the Sahara, as well as the formation of extensive lakes throughout the Sahara would generate significant feedbacks to the climate system. Finally, a better understanding of the frequency and intensity of North African pluvial phases would allow for a re-evaluation of the extent to which the Sahara acted as a barrier to the dispersal of modern humans out of Africa during the Quaternary Period, an important concern in human origins research.Broader impacts of the proposed work include the fostering of cooperation and collaboration with Egyptian scientists through the hosting of a short course on field techniques in Quaternary geology and geomorphology in Dakhleh Oasis. This work forms the basis of a Ph. D. for one of the PI.s female graduate students. The climate chronology is deposited with the web-based World Data Center for Paleoclimatology database, allowing widespread use. Samples collected during field work become part of a course on paleoenvironmental reconstruction.