Collaborative Research: Holocene and Late Pleistocene Stream Deposition in the McMurdo Dry Valleys, Antarctica as a Proxy for Glacial Meltwater and Paleoclimate

麦克默多干谷是南极洲最大的无冰地区，拥有季节性活跃的水文系统，有溪流和咸水湖。溪流的水源来自当地冰川和雪堤的夏季融化水。因此，径流与夏季气候条件有关，如气温、地面温度、风和即将到来的太阳辐射。根据50年的监测，观察到夏季溪流活动发生了变化，在过去的地质时期，它可能会随着区域气候变化和冰川波动而发生变化。因此，来自这些溪流的沉积物可以解决有关该地区过去气候、融化水和湖泊水位变化的问题。融水径流对过去的气候变化有何反应？在冰川进退期，水流是如何变化的？大型湖泊在什么时候填满了许多山谷？它们的范围有多大？研究人员计划获取干旱山谷的溪流活动记录，该山谷将跨越三个最大的山谷，时间周期约为10万年。这一记录将来自一系列活跃的古代冲积扇，这些冲积扇是由溪流从山谷侧壁流到山谷底部时沉积的。这项研究将提供一个长期背景，用来评估最近观察到的河流活动和湖泊水位的变化。这项研究将由两名职业生涯中期的女性调查人员领导，并为学生的研究机会和教育做出重大贡献。这项研究将把学生纳入实地和实验室研究，并将数据和结果纳入课堂，从而为研究生和本科教育做出贡献。这项研究将通过外展向K-12和非科学社区传播，包括对马萨诸塞州东部的K-12教师进行专业发展培训，开展动手活动，访问K-12教室，以及北卡罗来纳州的STEM教育和扫盲活动。PIS建议限制全新世和晚更新世期间麦克默多干燥山谷的河流沉积速度和河流活动增加的时期。在对干旱河谷进行了50年的水文监测期间，科学家们观察到溪流对夏季条件表现出显著的响应。以前对冰川和湖泊沉积的研究表明，在最近的间冰期，干燥山谷中的冰川区域推进，在末次冰盛期(LGM)期间和之后，湖泊水位较高，在全新世期间可能出现显著的低水位和高水位。然而，融水活动的地质记录并没有受到很大的限制。PI试图通过分析和测定冲积扇的年代来开发第一个空间上广泛的干谷河流沉积记录。考虑到冲积扇是由夏季融水流在相对稳定的构造环境中沉积的，这一记录将作为区域夏季气候条件的替代。融水溪流是区域水文系统的重要组成部分，将冰川与湖泊连接起来，并影响生态系统和土壤。河流沉积的记录是理解过去气候变化和区域水文之间关系的关键。拟议的研究将包括冲积扇、河流渠道和融水源的远程和现场测绘，以及模拟南半球夏季可能传入到扇和水汽来源的太阳辐射。在野外，PI将记录地层，从四个山谷(泰勒、皮尔斯、赖特和维多利亚)的25个扇体收集近地表沉积物，并从三个冲积扇复合体收集2-3米垂直冰胶结岩芯。然后，PI将通过光激发发光对河流砂岩进行沉积测年，并利用X射线粉末衍射和X射线荧光分析矿物学和主体常量元素化学。根据这些分析，PI建议(1)确定局部到区域尺度的高河流沉积时期的时间，(2)计算沉积速率，(3)限制沉积环境和沉积物来源。考虑到许多冲积扇出现在莱特山谷和维多利亚山谷冰川堰塞湖的假设最大范围以下，这些扇的详细地层、沉积物来源和OSL测年可能会为正在进行的关于末次盛冰期和末次盛冰期后湖泊的时间和范围的辩论提供线索。这项工作将支持一名博士后研究员、一名博士生以及许多本科生和硕士生进行跨学科研究，涉及地层学、地球化学、古气候学和物理学。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The McMurdo Dry Valleys are the largest ice-free region in Antarctica and home to a seasonally active hydrologic system, with streams and saline lakes. Streams are fed by summer meltwater from local glaciers and snowbanks. Therefore, streamflow is tied to summer climate conditions such as air temperatures, ground temperatures, winds, and incoming solar radiation. Based on 50 years of monitoring, summer stream activity has been observed to change, and it likely varied during the geologic past in response to regional climate change and fluctuating glaciers. Thus, deposits from these streams can address questions about past climate, meltwater, and lake level changes in this region. How did meltwater streamflow respond to past climate change? How did streamflow vary during periods of glacial advance and retreat? At what times did large lakes fill many of the valleys and what was their extent? The researchers plan to acquire a record of stream activity for the Dry Valleys that will span the three largest valleys and a time period of about 100,000 years. This record will come from a series of active and ancient alluvial fans that were deposited by streams as they flowed from valley sidewalls onto valley floors. The study will provide a long-term context with which to assess recent observed changes to stream activity and lake levels. The research will be led by two female mid-career investigators and contribute significantly to student research opportunities and education. The research will contribute to graduate and undergraduate education by including students in both field and laboratory research, as well as incorporating data and results into the classroom. The research will be disseminated to K-12 and non-scientific communities through outreach that includes professional development training for K-12 teachers in eastern Massachusetts, development of hands-on activities, visits to K-12 classrooms, and STEM education and literacy activities in North Carolina.The PIs propose to constrain rates of fluvial deposition and periods of increased fluvial activity in the McMurdo Dry Valleys during the Holocene and late Pleistocene. During 50 years of hydrologic monitoring in the Dry Valleys, scientists have observed that streams exhibit significant response to summer conditions. Previous studies of glacial and lacustrine deposits indicate regional glacier advance in the Dry Valleys during recent interglacial periods and high lake levels during and after the Last Glacial Maximum (LGM), with potentially significant low and high stands during the Holocene. However, the geologic record of meltwater activity is poorly constrained. The PIs seek to develop the first spatially-extensive record of stream deposition in the Dry Valleys by analyzing and dating alluvial fans. Given that alluvial fans are deposited by summer meltwater streams in a relatively stable tectonic setting, this record will serve as a proxy of regional summer climate conditions. Meltwater streams are an important component of the regional hydrologic system, connecting glaciers to lakes and affecting ecosystems and soils. A record of fluvial deposition is key to understanding the relationship between past climate change and regional hydrology. The proposed research will include remote- and field-based mapping of alluvial fans, stream channels, and meltwater sources as well as modeling potential incoming solar radiation to the fans and moisture sources during the austral summer. In the field, the PIs will document stratigraphy, collect near-surface sediments from 25 fans across four valleys (Taylor, Pearse, Wright, and Victoria), and collect 2- to 3-m vertical cores of ice-cemented sediments from three alluvial fan complexes. The PIs will then conduct depositional dating of fluvial sands via optically stimulated luminescence and analyze mineralogy and bulk major element chemistry with X-ray powder diffraction and X-ray fluorescence. From these analyses, the PIs propose to (1) determine the timing of local- to regional-scale periods of high fluvial deposition, (2) calculate depositional rates, and (3) constrain depositional environments and sediment provenance. Given that many of the alluvial fans occur below the hypothesized maximum extents of glacially-dammed lakes in Wright and Victoria valleys, detailed stratigraphy, sediment provenance, and OSL dating of these fans could shed light on ongoing debates regarding the timing and extent of LGM and post-LGM lakes. The work will support a postdoctoral researcher, a PhD student, and many undergraduate and master’s students in cross-disciplinary research that spans stratigraphy, geochemistry, paleoclimatology and physics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.