Isotope Paleohydrology of Lakes Albert, Edward and Victoria, East Africa

9706522东非的大湖是大陆尺度热带水文的敏感监测器，它们提供了长期连续的十年尺度的水平衡和温度档案，以检验热带海洋水分输送的演变模式。我们的问题是如何解读和量化这些签名。该地区先前的研究缺乏明确区分温度和降水影响所必需的工具。相比之下，本研究提出了应用水生纤维素和脂质的氧和氢同位素分析新技术，这将使我们能够区分降水信号。目的是量化过去15000年来阿尔伯特湖、爱德华湖和维多利亚湖水平衡变化的幅度和时间，并确定它们对当地和区域生物圈的影响。这些湖泊中水动力学的时间序列也将与尼罗河沿岸植被和文明的历史进行比较。工作计划包括建立现代陆生和水生纤维素/ 18O数据库，以确定与温度无关和与物种无关的水生纤维素氧同位素生化分馏因子。该数据库将用于约束古水文解释。对所有三个湖泊的可用岩心样本进行少于300年增量的分析，将提供水生纤维素，从而提供过去15,000年的湖水氧同位素时间序列剖面。湖泊水体的主要氧同位素信号来源于P:E比值和停留时间的变化，地下水和高山水的影响可以忽略不计。对水生脂类的进一步分析有望反映湖水的D值。仔细考虑流域和湖泊水文之间的相互作用，以及过去的海洋同位素值，可以对这些盆地的水汽来源（大西洋与印度洋）的历史进行测试。该研究为热带地区的古水文研究提供了敏感的新方法，并有助于限制古气候模式的预测。

9706522 The large lakes of East Africa are sensitive monitors of continental-scale tropical hydrology that provide long continuous decadal-scale archives of water balance and temperature to test evolving models of tropical ocean moisture transport. Our problems is to read and quantify such signatures. Prior studies in the region have lacked the tools necessary to unequivocally separate temperature and precipitation effects. In contrast, this study proposes to apply new techniques of oxygen and hydrogen isotopic analyses of aquatic cellulose and lipids that will allow us to differentiate the precipitation signal. The objectives are to quantify the magnitude and timing of shifts in the water balances of Lakes Albert, Edward, and Victoria over the last 15,000 years and determine their implications for the local and regional biosphere. The time-series of water dynamics in these lakes will also be compared with the history of vegetation and civilization along the Nile. The workplan includes compilation of a modern terrestrial and aquatic cellulose/ 18O database to confirm the temperature-independent and species-independent oxygen isotopic biochemical fractionation factor of aquatic cellulose. This database will be used to constrain paleohydrologic interpretations. Analyses of available core samples from all three lakes at less than 300 year increments will provide aquatic cellulose and hence lake water oxygen isotopic time-series profiles over the last 15,000 years. These primary oxygen isotopic signals of the lake waters will derive from shifts in P:E ratios and residence times with negligible groundwater and high mountain water effects. Additional analyses in aquatic lipids are expected to reflect D values of the lake water. Careful consideration of interactions between the watershed and lake water hydrologies as well as of past ocean isotopic values may allow testing for the history of moisture sources (Atlantic vs. Indian Ocean) to these basin. This study should provide sensi tive new approaches to the study of paleohydrology in tropical regions and help constrain paleoclimate model predictions.