EAGER - feasibility study in reconstructing Holocene drought history from sediment cores in Fallen Leaf Lake, CA

美国西部的研究表明，在过去10- 13000年（全新世）干旱模式的深刻，长期变化对生态系统和人类产生了历史和史前影响。这项赠款将从内华达州北方塞拉山脉的沉积物岩心中开发一个长期干旱记录，这是一个气候敏感地区。该项目将侧重于流域的高山部分，那里冬季降水不足的影响比终端湖泊流域更直接可测量。这些影响包括在干旱阶段降低湖泊水位，温暖的湖泊温度，热分层的强度和深度的变化，以及改变生物结构。特别是，湖泊沉积物中的化石硅藻群落预计会因干旱而变化，并可用作气候变化和长期干旱的指标。一个很好的硅藻记录可能存在于太浩湖流域落叶湖的沉积物作为古气候指标，预计几十年到百年的分辨率。2010年采集的岩心初步年龄模型显示，很有希望制定详细的年表。岩芯包含了13，300年前的连续记录，沉积速率平均为1.4毫米/年。该团队将测试亚高山湖泊沉积物中的硅藻是否可以作为冬季降水变化的指标，以及硅藻，沉积学和选定的地球化学指标的变化是否与中世纪气候异常和其他全新世长期干旱期间的干旱条件有关。该湖是一个很好的选择，因为它记录了大量的降水驱动的湖平面变化，该地区的水平衡和水文响应干旱是可测量的。初步数据表明，硅藻物种数量的变化与有据可查的数百年干旱有关。该团队将通过观察离散样本的有机地球化学（%有机质和C，N同位素），化合物特定地球化学和花粉分析来研究硅藻对干旱条件的反应。此外，该团队还将以高分辨率（0.2-0.5mm）对生物二氧化硅和有机物含量进行X射线荧光扫描。将使用各种多变量和交叉频谱技术对所有核心代用数据进行交叉相关。区域树木年轮气候记录将被用作验证水文变率的一种独立手段。拟议的研究对社会有更大的影响，这些数据应该引起关注淡水水生系统对气候变化长期反应的水生生态学家、自然资源管理者和气候科学家的兴趣。长期干旱的时间和影响也将引起人类学家的兴趣，他们将重建美洲原住民在干旱条件下的迁徙，包括北方派尤特人、迈杜人、瓦肖人、约库特人和西莫诺人的祖先。此外，更好地将硅藻作为气候变化指标的努力可以增加用于解释区域气候变化及其对人类活动的相关影响的工具数量。该项目将提供建立高质量年龄模型所需的年龄和扫描XRF分析，并为这套全新世岩心建立基本的沉积学框架。这个框架是所有正在进行的古生物学和地球化学工作的必要的第一步，这些工作是由各种研究生和教职员工正在进行的。它还将提供各种专门指标（硅藻、有机地球化学、花粉分析）所需的离散样品和硅藻工作所需的分析。目前，5名研究生依靠这些岩心进行论文和学位论文研究，并将通过额外的年龄控制，地球化学数据和样品受益匪浅。岩芯和数据将在明尼苏达州国家湖泊岩芯储存库存档。

Work in the western US indicates that profound, long-term shifts in patterns of drought throughout the past 10-13,000 years (the Holocene) have had both historic and prehistoric impact on ecosystems and on humans. This grant will develop a long-term drought record from sediment cores in the northern Sierra Nevada, a climatically sensitive region. The project will focus on the alpine portion of the watershed where the effects of winter precipitation deficits are more directly measurable than in terminal lake basins. These effects include lowered lake levels during drought stages, warmer lake temperatures, variations in strength and depth of thermal stratification, and altered biotic structure. In particular, fossil diatom communities in lake sediments are expected to vary in response to drought, and may be used as a indicators of climate change and long-lasting droughts. An excellent diatom record potentially exists in sediments of Fallen Leaf Lake in the Lake Tahoe watershed for use as paleoclimate indicators, with expected multi-decadal to centennial resolution. Preliminary age models on cores taken in 2010 show great promise for developing a detailed chronology. The cores contain a continuous record extending back 13,300 yrs, with sedimentation rates averaging 1.4 mm/year. The team will test whether diatoms in sub-alpine lake sediment can serve as indicators of changes in winter precipitation, and whether changes in diatom, sedimentologic, and selected geochemical indicators can be related to drought conditions during the Medieval Climatic Anomaly and other Holocene long-term droughts. The lake is a good choice because it records large precipitation-driven lake level shifts, and the area's water balance and hydrologic response to drought is measurable. Preliminary data indicates shifts in the number of diatom species associated with a well documented multi-hundred year drought. The team will investigate diatom response to drought conditions by looking at organic geochemistry from discrete samples (% organic matter and C, N isotopes), compound specific geochemistry, and pollen analysis. In addition, the team will conduct X-ray fluorescence scans for biogenic silica and organic matter content at high resolution (0.2-0.5mm). All core proxy data will be cross-correlated using a variety of multivariate and cross spectral techniques. Regional tree-ring climatic records will be used as an independent means of validating hydrological variability.The proposed research has larger impacts to society, and this data should be of interest to aquatic ecologists, natural resource managers, and climate scientists concerned with the long-term response of fresh-water aquatic systems to climatic change. The timing and effects of prolonged drought will also be of interest to anthropologists reconstructing the migrations of Native Americans in response to drier conditions, including the ancestors of the Northern Paiute, the Maidu, the Washoe, the Yokuts, and the West Mono. Further, this effort to better establish diatoms as indicators of climate variation could add to the number of tools used to interpret regional climate change, and its associated impacts on human activities. This project will provide ages and scanning XRF analyses needed to build a quality age model, and establish the basic sedimentologic framework for this set of Holocene cores. This framework is a necessary first step for all of the ongoing paleontologic and geochemical work that is underway with these cores by various graduate students and faculty members. It will also provide the discrete samples needed for the various specialized indicators (diatoms, organic geochemistry, pollen analysis) and analyses necessary for the diatom work. At present, 5 graduate students rely on these cores for their thesis and dissertation research, and will benefit greatly by additional age control, geochemical data, and samples. Cores and data will be archived at the National Lacustrine Core Repository, Minnesota.