Late Holocene Climate Variability From Eolian Lake Sediments in Relict San Luis Lakes

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。古气候研究从各种来源(如树轮、洞穴沉积物、海岸线、海滩沉积物和湖泊沉积物等)获得了许多替代记录。并提供了有关全新世晚期西南地区气候波动的重要信息。尽管如此，关于美国西南部晚全新世气候变异性的记录还远远没有完成。对于这一地区，记录三种不同气候系统的全流域特定季节历史的代理记录很少：冬季风暴、春季沙尘暴和暖季季风。特别是，对该地区过去沙尘暴动力学的变化知之甚少。根据其他人之前的工作和2007年7月从残存的圣路易斯湖采集的两个表层岩芯的初步结果，PI认为圣路易斯湖主要是风成沉积物夹层河流沉积，以及干涸湖泊的通货紧缩造成的离散缺失记录。对较长沉积岩芯的研究将使他们能够认识到该地区晚全新世气候变异性的主要强迫机制。他们正在研究圣路易斯湖沉积物的年代学、沉积学、元素和同位素地球化学，以重建美国西南部全新世晚期的十年变化，特别关注中世纪暖期和小冰期这两个截然不同的时期。该小组将从圣路易斯河谷封闭盆地地区的两个不同湖泊采集两个5米长的沉积物岩芯，通过对岩心下部沉积物中石英颗粒的光激发发光(OSL)分析和有机物质的放射性碳(14C)测年，建立沉积物年代学，并对岩心下部沉积物进行一系列沉积学、地球化学和同位素分析(磁化率、粒度分布、碳酸盐矿物学、镁/钙和Del-18O，这项研究的结果满足了美国西南部广大干旱地区的区域水资源管理的需要，该地区目前正在经历人口和经济的快速增长，并有助于了解圣路易斯湖在大沙丘(GSD)开发中的作用。该项目使生活在格兰德河谷的人们、研究美洲原住民居住模式的考古学家、研究GSD风沙系统的地质学家以及参观GSD的普通公众受益。该项目涉及两名本科生和一名研究生助理的现场和实验室工作。该项目的更广泛影响还包括1)促进与该领域知名科学家的多机构合作，2)培训本科生和研究生，3)在会议和同行评议的期刊出版物上传播研究成果。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Paleoclimate research has yielded a number of proxy records from a variety of sources (e.g. tree rings, cave deposits, shorelines, beach deposits, and lake sediments etc.) in the American Southwest and provided important information of southwest climate fluctuations during the late Holocene. Nevertheless, the documentation of late Holocene climate variability in the American Southwest is far from complete. For this area, proxy records documenting basin wide season-specific history of three distinct climatic systems are scarce: for winter storms, spring dust storms, and warm-season monsoons. In particular, little is known of past changes in dust storm dynamics in this region.On the basis of previous work by others and preliminary results of two surface cores taken from relict San Luis Lakes in July 2007, the PIs believe that San Luis Lakes were dominated by eolian sediments intercalated with fluvial deposits along with discrete missing records caused by deflation of dried-out lakes. Examination of longer sediment cores will allow them to recognize the dominant forcing mechanisms of late Holocene climatic variability in this region. They are studying the chronology, sedimentology, elemental and isotope geochemistry of sediments from San Luis Lakes to reconstruct decadally-resolved late Holocene variability in the American Southwest, with special attention to the two contrasting epochs of the Medieval Warm Episode and the Little Ice Age. The team will collect two 5-m-long sediment cores from two different lakes in the closed-basin area of the San Luis Valley, develop a sediment chronology through optically stimulated luminescence (OSL) analysis of quartz grains and radiocarbon (14C) dating of organic materials in downcore sediments, and conduct a series of sedimentological, geochemical and isotopic analyses of downcore sediments (magnetic susceptibility, grain size distribution, carbonate mineralogy, Mg/Ca and del-18O, etc).The results of this research serve the needs for policy makers of regional water resources management for the vast dryland region in the American Southwest currently undergoing rapid growth of population and economy and also help to understand the role of the San Luis Lakes in the development of the Great Sand Dunes (GSD). This project benefits people living in the Rio Grande valley, archeologists working on the habitation patterns of Native Americans, geologists studying the GSD eolian system, and the general public visiting the GSD. This project involves two undergraduate students and one graduate assistant in the field and laboratory work. The broader impacts of this project also include 1) fostering multi-institutional collaboration with established scientists in the field, 2) training undergraduate and graduate students, and 3) disseminating research findings at conferences and peer-reviewed journal publications.