Collaborative Research: Absolute-dated records of Late Quaternary paleohydrology in the Bonneville Basin, western U.S., from novel cave archives

技术摘要美国大盆地的水量平衡在很大程度上反映了西风风暴路径的位置和强度，这表明过去水文变化的记录为了解不同气候状态下风暴路径的行为提供了重要的见解。然而，有限的测年精度和样本分辨率的现有记录过去的水平衡，离开科学家无法解决的问题，精确的时间和过去的水平衡变化率，以及它们与其他古气候档案记录的突发事件的关系。此外，很少有明确的记录延续到末次冰期之后，这使得人们对以前的间冰期和冰川终止的了解很少。该项目将利用洞穴沉积物重建Bonneville盆地过去突然的水平衡变化，Bonneville盆地是最后一次冰期大盆地最大的古湖泊所在地。这项工作借鉴了a）湖相洞穴沉积物，形成于一系列被湖泊沃茨淹没的洞穴中，以及B）盆地西南边缘雷曼洞穴的洞穴沉积物。使用稳定同位素测量和U-Th和14 C测年的组合，该小组将能够产生前所未有的测年精度和样本分辨率的记录，涵盖最近的冰川终止以及前两次间冰期和终止。来自湖相洞穴沉积物的数据，一种新的古水文档案，表明它们形成于过去30 kyr的时期，当时湖泊都在给定的洞穴上方？的海拔高度和水文关闭。因此，这些沉积物记录了湖泊通过每个洞穴的高度以及盆地溢出的开始和停止;它们还保存了湖泊氧同位素组成和化学的高分辨率记录。重要的是，这些沉积物可以通过U-Th方法精确测定年代，这是第一个高精度的、绝对年代的邦纳维尔湖水平衡变化记录。校准的14 C年龄相匹配的湖相洞穴沉积物中的U-Th年龄，表明14 C水库的影响是最小的湖。作为该项目的一部分，一系列成对的U-Th和14 C年龄将被用来改善14 C校准数据集，集中在19和25万年之间的时期。雷曼洞穴洞穴的洞穴沉积物包括一个重要的补充，湖相洞穴碳酸盐岩，延伸回通过过去300 kyr的大部分。洞穴石笋的稳定同位素记录，锚定U-Th日期，将提供一些第一个良好的地区水文档案在前两个间冰期和冰川终止。雷曼洞穴和湖相洞穴的记录一起提供了关于大盆地东部在最近三个冰期周期中对突然的和轨道尺度的气候变化的反应的关键见解。非技术性摘要模型一致预测，由于温室效应，世界上的旱地平均将变得更干燥，但目前还不清楚这种干燥将如何影响特定地区。在美国，人们特别有兴趣了解大盆地未来干旱的可能性，大盆地是一个干旱易发地区，过去二十年来人口大量增长。过去的水资源记录为预测大盆地未来的变化提供了一个关键的起点，它向我们展示了该地区对各种气候的反应。在过去的3万年里，美国西部内陆大盆地的降水和蒸发平衡发生了巨大的变化，留下了今天的干涸湖床和高盐度湖泊，而在冰川时代存在着广泛的湖泊。该地区的水资源供应在很大程度上取决于冬季风暴轴带来的降水，这表明过去的水文变化记录提供了重要的见解风暴轴在不同的气候状态下的行为。然而，有限的测年精度和样本分辨率的记录，留给我们的只是一个一般意义上的过去的水文变化，并没有良好的记录，目前延伸到过去的间冰期warm periods.This项目将使用洞穴沉积物重建过去的水平衡变化在北方犹他州的博内维尔盆地，大盆地的古湖泊最大的网站。这些沉积物记录了过去30万年来盆地降水量的变化，并能够精确地确定日期，使我们有机会构建该地区过去气候变化的详细和扩展图片。重要的是，石笋从莱曼洞的盆地西部边缘记录了最后两个间冰期温暖的时期，使我们有机会研究该地区的水文的平均状态和变化的时候，该地区是温暖的或略高于现在。这项工作对我们了解过去的气候变化做出了重要贡献，并将有助于校准试图重现过去变化的模型，以便更好地预测未来。此外，这些记录将有助于我们解释流域过去的生态变化和该地区早期人类占领的历史。

TECHNICAL ABSTRACTWater balance in the U.S. Great Basin largely reflects the position and intensity of the westerly storm track, suggesting that records of past hydrologic changes offer important insights into the behavior of the storm track in different climate states. The limited dating precision and sample resolution of presently available records of past water balance, however, leave scientists unable to address questions about the precise timing and rates of past water balance changes and their relation to abrupt events recorded in other paleoclimate archives. Further, few well-dated records extend past the last glacial period, allowing little understanding of previous interglacials and glacial terminations. This project will use cave deposits to reconstruct past abrupt water balance changes in the Bonneville Basin, the site of the largest of the Great Basin's paleolakes during the last glacial period. The work draws upon both a) lacustrine cave deposits formed in a series of caves flooded by lake waters and b) speleothems from Lehman Cave on the southwestern edge of the basin. Using stable isotope measurements and a combination of U-Th and 14C dating, this group will be able to produce records with unprecedented dating precision and sample resolution covering the most recent glacial termination as well as the previous two interglacials and terminations. Data from lacustrine cave deposits, a novel paleohydrologic archive, indicate that they formed during periods of the last 30 kyr when the lake was both above a given cave?s elevation and hydrologically closed. The deposits thus record the passage of the lake through each cave's elevation and the onset and cessation of basin overflow; they also preserve high-resolution records of the lake's oxygen isotope composition and chemistry. Importantly, the deposits can be precisely dated by U-Th methods, providing the first high-precision, absolute-dated records of Lake Bonneville's water balance changes. Calibrated 14C ages match U-Th ages in lacustrine cave deposits, indicating that 14C reservoir effects were minimal in the lake. As a part of the project, a series of paired U-Th and 14C ages will be used to improve the 14C calibration dataset, focusing on the period between 19 and 25 calendar ka.Lehman Cave speleothems comprise an important complement to the lacustrine cave carbonates, extending back through substantial portions of the last 300 kyr. Stable isotope records from the cave's stalagmites, anchored by U-Th dates, will provide some of the first well-dated archives of regional hydrology during the previous two interglacials and glacial terminations. Together, Lehman Cave and lacustrine cave records promise key insights into the eastern Great Basin's response to both abrupt and orbital-scale climate changes during the last three glacial cycles.NON-TECHNICAL ABSTRACTModels consistently predict that the world's drylands will become drier on average in response to greenhouse warming, but it is unclear how this drying will affect specific regions. In the U.S., there is particular interest in understanding the potential for future drying in the Great Basin, a drought-prone region that has experienced substantial population growth over the last two decades. Records of past water availability provide a key starting point for forecasting future changes in the Great Basin by showing us the region's responses to a wide variety of climates.The balance of precipitation and evaporation in the Great Basin in the western interior of the U.S.A. has changed dramatically over the past 30,000 years, leaving dry lake beds and hypersaline lakes today where extensive lakes existed during glacial times. Water availability in the region largely depends upon precipitation brought by the winter storm track, suggesting that records of past hydrologic changes offer important insights into the behavior of the storm track in different climate states. The limited dating precision and sample resolution of present records, however, leave us with only a general sense of past hydrologic changes, and no well-dated records currently extend to past interglacial warm periods.This project will use cave deposits to reconstruct past water balance changes in northern Utah's Bonneville Basin, the site of the largest of the Great Basin's paleolakes. These deposits record changes in precipitation in the basin over much of the past 300,000 years and are able to be precisely dated, offering us the opportunity to construct a detailed and extended picture of past climate changes in the region. Importantly, stalagmites from Lehman Cave on the western edge of the basin record the last two interglacial warm periods, allowing us the opportunity to study the mean state and variability of the region's hydrology during times when the region was as warm as or slightly warmer than at present. This work represents an important contribution to our understanding of past climate changes and will help calibrate models seeking to reproduce past changes in order to better forecast the future. In addition, these records will assist us in interpreting past ecological changes in the basin and the history of early human occupation in the region.