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区，拥有季节性活跃的水文系统，有溪流和盐湖。溪流由当地冰川和雪堤的夏季融水提供水源。因此，径流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。根据50年的监测，夏季溪流活动已经观察到变化，它可能在地质过去的变化，以应对区域气候变化和波动的冰川。因此，这些溪流的沉积物可以解决该地区过去气候，融水和湖泊水位变化的问题。冰川融水如何应对过去的气候变化？在冰川前进和后退期间，河流流量是如何变化的？在什么时候大湖泊填补了许多山谷和他们的范围是什么？研究人员计划获得干旱山谷的溪流活动记录，该记录将跨越三个最大的山谷，时间约为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谷底时沉积的。这项研究将提供一个长期的背景，以评估最近观察到的溪流活动和湖泊水位的变化。该研究将由两名女性职业中期调查员领导，并为学生的研究机会和教育做出重大贡献。这项研究将有助于研究生和本科教育，包括学生在现场和实验室研究，以及将数据和结果纳入课堂。这项研究将通过外展活动传播到K-12和非科学社区，包括马萨诸塞州东部K-12教师的专业发展培训，实践活动的开展，K-12教室的参观，以及北卡罗来纳州的STEM教育和扫盲活动。PI建议在2010年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。全新世和晚更新世。在干旱河谷50年的水文监测中，科学家们观察到溪流对夏季条件有明显的反应。以往的研究表明，冰川和湖泊沉积物在最近的间冰期和高湖泊水位期间和之后的末次冰期最大（LGM），潜在的显着的低和高的立场在全新世干旱河谷的区域冰川前进。然而，融水活动的地质记录缺乏约束。PI试图通过分析和确定冲积扇的年代来开发干旱山谷中河流沉积的第一个空间广泛的记录。鉴于冲积扇沉积的夏季融水流在一个相对稳定的构造环境，这一记录将作为一个代理的区域夏季气候条件。融水流是区域水文系统的重要组成部分，连接冰川和湖泊，影响生态系统和土壤。河流沉积记录是理解过去气候变化与区域水文之间关系的关键。拟议中的研究将包括冲积扇，河道和融水源的远程和实地测绘，以及在南方夏季模拟潜在的太阳辐射到风扇和水分来源。在野外，PI将记录地层学，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至3米的冰胶结沉积物垂直岩心。然后，PI将通过光激发光对河流砂进行沉积年代测定，并通过X射线粉末衍射和X射线荧光分析矿物学和大量主要元素化学。根据这些分析，PI建议（1）确定局部到区域规模的高河流沉积期的时间，（2）计算沉积速率，（3）限制沉积环境和沉积物来源。鉴于许多冲积扇发生在赖特和维多利亚山谷的冰川堰塞湖的假设最大范围之下，详细的地层学，沉积物来源和这些风扇的光释光测年可以揭示正在进行的辩论的时间和范围LGM和后LGM湖泊。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，涵盖地层学、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.