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，也是季节性活跃的水文系统的所在地，有溪流和盐湖。溪流的水源来自当地冰川和雪滩的夏季融水。因此，河流流量与夏季气候条件有关，如气温、地面温度、风和入射的太阳辐射。基于50年的监测，夏季河流活动已经观察到变化，并且它可能在过去的地质时期随着区域气候变化和冰川波动而变化。因此，这些溪流的沉积物可以解决有关该地区过去气候、融水和湖泊水位变化的问题。融水流是如何对过去的气候变化做出反应的？在冰川前进和后退期间，水流是如何变化的？在什么时候大型湖泊填满了许多山谷？它们的范围有多大？研究人员计划获取干谷的河流活动记录，该记录将跨越三个最大的山谷，时间跨度约为10万年。这一记录将来自于一系列活跃的古代冲积扇，这些冲积扇是由河流从山谷的侧壁流到谷底时沉积下来的。这项研究将提供一个长期的背景，以评估最近观察到的河流活动和湖泊水位的变化。这项研究将由两名处于职业生涯中期的女性调查员领导，并为学生的研究机会和教育做出重大贡献。这项研究将通过让学生参与实地和实验室研究，并将数据和结果纳入课堂，为研究生和本科教育做出贡献。这项研究将通过对马萨诸塞州东部K-12教师的专业发展培训、开展实践活动、参观K-12教室以及北卡罗来纳州的STEM教育和扫盲活动等外展活动，传播到K-12和非科学社区。PIs建议在全新世和晚更新世期间限制麦克默多干谷的河流沉积率和河流活动增加的时期。在对干谷50年的水文监测中，科学家们观察到，河流对夏季条件表现出显著的反应。先前对冰川和湖泊沉积的研究表明，在最近的间冰期，干谷的区域冰川在推进，在末次盛冰期（LGM）期间和之后的湖泊水位较高，在全新世期间可能存在显著的低洼和高洼。然而，关于融水活动的地质记录很少。通过对冲积扇的分析和定年，pi试图在干谷中开发第一个空间广泛的河流沉积记录。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代表。融水流是区域水文系统的重要组成部分，连接着冰川和湖泊，影响着生态系统和土壤。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。拟议的研究将包括对冲积扇、河道和融水源的远程和实地测绘，以及在南方夏季对扇和湿气源的潜在太阳辐射的建模。在现场，pi将记录地层学，从四个山谷（Taylor, Pearse， Wright和Victoria）的25个扇中收集近地表沉积物，并从三个冲积扇复群中收集2至3米的垂直冰结沉积物岩心。然后，pi将通过光学激发发光对河流砂进行沉积测年，并使用x射线粉末衍射和x射线荧光分析矿物学和主要元素化学。根据这些分析，PIs建议(1)确定局部到区域高河流沉积期的时间，(2)计算沉积速率，(3)约束沉积环境和沉积物物源。考虑到许多冲积扇发生在赖特和维多利亚山谷中冰川坝湖泊的假设最大范围以下，这些扇的详细地层学，沉积物来源和OSL定年可以阐明关于LGM和后LGM湖泊的时间和范围的持续争论。这项工作将支持一名博士后研究员、一名博士生以及多名本科生和硕士生进行跨地层学、地球化学、古气候学和物理学的跨学科研究。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.