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程度，并评估这些事件与东太平洋条件的联系，对于加州和美国西南部邻近地区的长期水资源规划至关重要。这个博士论文研究项目将使用保存在气候敏感的Sierran小湖泊沉积物中的水生生物遗骸，特别是蠓幼虫，重建晚期第四纪（过去13000年）加利福尼亚古温度和古水文的高分辨率记录。这项研究是对早期nsf支持的一个项目的扩展，该项目评估了当今气温和降水、湖水温度、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Sierran湖沉积物中发现的chironomids（蠓）、cladocera（甲壳类动物）、硅藻（单细胞藻类）、花粉和气孔中。先前的工作已经确定，Sierran湖泊中蠓的现代分布受夏季湖面水温、湖泊深度、海拔和铁的控制。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），还描述了蠓分布与湖表面水温之间的关系。本论文将新的传递函数应用于晚第四纪湖泊沉积物岩心中的蚊化石组合，从而实现加州晚第四纪古温度的高分辨率重建。内华达山脉早期的古环境研究表明，在全新世晚期（最近3000年），加利福尼亚东部发生了比仪器记录时期（过去100年）所经历的更严重的干旱事件。然而，由于现有古环境记录的碎片性，对早期干旱期的理解是有限的。这个研究项目将提供过去13000年来加州东部气候固有变化的高分辨率记录。更具体地说，该项目将使用保存在塞拉兰湖沉积物中的蚊幼虫遗骸，为过去13000年来发生在加州内华达山脉东部的气候变化提供敏感而详细的历史。这项工作的结果将有助于水文学家、古气候学家、海洋学家和气候建模者了解加州晚第四纪高频气候振荡的时间、幅度和因果机制。预期的结果应有助于水资源管理人员设法充分规划未来的水资源需要。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.