Doctoral Dissertation Research: High-Resolution Time Series of Eastern Sierra California Climate Over the Late Quaternary

了解过去干旱事件的严重性，并评估这些事件与东太平洋情况的联系，对于加利福尼亚州和美国西南部邻近地区的长期水资源规划至关重要。这项博士论文研究项目将利用保存在对气候敏感的小型锡尔兰湖沉积物中的水生生物，特别是蚊蝇幼虫的遗骸，重建晚第四纪(过去13,000年)加州古温度和古水文的高分辨率记录。这项研究是早些时候NSF资助的一个项目的扩展，该项目评估了当今气温和降水、湖泊水温、盐度、深度和周围植被的差异如何反映在湖水的现代元素化学和氧同位素组成中，以及在锡尔然湖沉积物中发现的摇蚊(蚊虫)、枝角类(甲壳类)、硅藻(单细胞藻类)、花粉和气孔。以前的工作已经确定，锡尔然湖的现代蚊类分布是由夏季表层湖水温度、湖深、海拔和铁控制的。此外，还通过建立传递函数(将特定环境变量的值表示为植物或动物物种组成数据的函数的数学公式)来表征蚊虫分布与表层湖水温度之间的关系。这篇论文的研究项目将把新的传递函数应用于晚第四纪湖泊沉积岩芯中包含的化石侏儒组合，从而能够高分辨率地重建晚第四纪加州的古温度。内华达山脉早期的古环境研究表明，加州东部在晚全新世(最后3000年)发生了比仪器时期(过去100年)更严重的干旱事件。然而，由于现有古环境记录的碎片性，人们对早期干旱时期的了解有限。这项研究项目将提供过去13,000年来加州东部气候内在变异性的高分辨率记录。更具体地说，该项目将利用保存在Sierran湖沉积物中的蚊蝇幼虫遗骸，提供过去13,000年来加利福尼亚州内华达山脉东部发生的气候变化的敏感和详细的历史。这项工作的结果将有助于水文学家、古气候学家、海洋学家和气候模型师理解与加州第四纪晚期明显的高频气候振荡相关的时间、强度和原因机制。预期成果应有助于水资源管理人员为未来的水资源需求进行充分规划。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。

Understanding the severity of past drought events and assessing the linkages of these events to conditions in the eastern Pacific is essential for long-term water resource planning in California and adjacent portions of the southwestern United States. This doctoral dissertation research project will use the remains of aquatic organisms, specifically midge fly larvae, preserved within the sediments of small, climatically sensitive Sierran lakes to reconstruct a high-resolution record of paleotemperature and paleohydrology for California during the late-Quaternary (past 13,000 years). This research is an expansion of an earlier NSF-supported project that assessed how present-day differences in air temperature and precipitation, lake water temperature, salinity, depth, and surrounding vegetation are reflected in the modern elemental chemistry and oxygen isotopic composition of lake waters, and the chironomids (midge flies), cladocera (crustaceans), diatoms (unicellular algae), pollen, and stomates found in Sierran lake sediments. Previous work had determined that the modern distribution of midges in Sierran lakes is controlled by summer surface lake-water temperature, lake depth, elevation, and iron. The relationship between midge fly distributions and surface lake-water temperature also have been characterized through the development of a transfer function (mathematical formulae that express the value of a specific environmental variable as a function of plant or animal species composition data). This dissertation research project will apply the new transfer function to the fossil midge assemblages contained within late-Quaternary lake sediment cores, thereby enabling a high-resolution reconstruction of paleotemperature for California during the late-Quaternary.Earlier paleoenvironmental research in the Sierra Nevada indicates that drought events of greater severity than those experienced during the instrumental period (past 100 years) have occurred in eastern California during the late-Holocene (last 3,000 years). Because of the fragmentary nature of the existing paleoenvironmental records, however, understandings of earlier drought periods is limited. This research project will provide a high-resolution record of the inherent variability of eastern California climate during the past 13,000 years. More specifically, this project will use the remains of midge fly larvae preserved in Sierran lake sediments to provide a sensitive and detailed history of the climatic changes that occurred in the eastern Sierra Nevada, California over the last 13,000 years. The results of this work will assist hydrologists, paleoclimatologists, oceanographers, and climate modelers in understanding the timing, magnitude, and causal mechanisms associated with high frequency climate oscillations evident in California during the late-Quaternary. The expected results should assist water resource managers as they attempt to adequately plan for future water resource needs. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.