Collaborative Research: Investigating Four Decades of Ross Ice Shelf Subsurface Change with Historical and Modern Radar Sounding Data

该奖项全部或部分由2021年美国救援计划法案（公法117-2）资助。冰架通过在其底部和侧面提供支撑，在限制地面冰川冰向海洋流动方面发挥着关键作用。因此，影响冰架长期稳定性的过程可能影响南极冰盖对全球海平面上升的未来贡献。罗斯冰架是地球上最大的冰架，它支撑着南极洲西部和东部的大片地区。以前对现代冰速度的研究表明，罗斯冰架的质量损失大致与其质量增加相平衡。然而，最近的研究表明，冰架可能不处于稳定状态，自20世纪90年代末以来可能会长期变薄。因此，为了准确地解释现代冰架的变化，长期观测对于评估这些最近的变化如何适应冰架变化的历史背景至关重要。该项目将研究罗斯冰架40多年的历史和现代机载雷达探测观测（跨越1971年至2017年），以调查十年时间尺度上的冰架变化。该团队将处理、校准和分析1971-79年野外活动期间收集的雷达数据，并将其与2011-17年期间收集的现代观测数据进行比较。 他们将通过检查冰架厚度的变化来估计基础融化率，并将确定融化的其他重要指标，包括冰架粗糙度，冰内温度和海冰形成。该项目将支持博士教育。三个参与机构的学生。此外，该项目还将支持培训放射冰川学和南极科学方面的本科生和高中研究人员，该项目将检验一种假设，即在十年的时间尺度内，罗斯冰架下的基底融化率一直很低，特别是在浅冰吃水的情况下，导致总体增厚和支撑潜力增加。该团队的目标是根据1971年至2017年期间发生的冰架厚度变化直接估计基底融化速率。该项目将扩展在Thwaites冰川完成的类似工作，并改进垂直比例的校准方法，以实现快速时间和深度转换。这项工作还将利用密集的现代调查，改进早期实地活动收集的雷达胶片的地理定位，以便更精确地比较当地大陆架厚度与现代数据。此外，该小组将进行冰内衰减分析，以计算冰内温度，从而推断当地基底融化的趋势。他们还将检查冰洋边界海床回波的辐射测量和散射测量特征，以表征冰架基底粗糙度、与局部基底冻结相关的海冰形成以及断裂过程造成的结构破坏的变化。该奖项反映了NSF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。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Ice shelves play a critical role in restricting the seaward flow of grounded glacier ice by providing buttressing at their bases and sides. Processes that affect the long-term stability of ice shelves can therefore influence the future contribution of the Antarctic Ice Sheet to global sea-level rise. The Ross Ice Shelf is the largest ice shelf on Earth, and it buttresses massive areas of West and East Antarctica. Previous studies of modern ice velocity indicated that the Ross Ice Shelf’s mass loss is roughly balanced by its mass gain. However, more recent work that extends further back in time reveals the ice shelf is likely not in steady state, with possible long-term thinning since the late 1990s. Consequently, to accurately interpret modern-day ice-shelf changes, long-term observations are critical to evaluate how these recent variations fit into the historical context of ice-shelf variability. This project will examine more than four decades of historical and modern airborne radar sounding observations of the Ross Ice Shelf (spanning 1971 to 2017) to investigate ice-shelf changes on decadal timescales. The team will process, calibrate, and analyze radar data collected during 1971-79 field campaigns and compare them against modern observations collected between 2011-17. They will estimate basal melt rates by examining changes in ice-shelf thickness, and will determine other important metrics for melt, including ice-shelf roughness, englacial temperature, and marine-ice formation. The project will support the education of a Ph.D. student at each of the three participating institutions. In addition, the project will support the training of undergraduate and high-school researchers in radioglaciology and Antarctic sciences.The project will test the hypothesis that, over decadal timescales, the basal melt rates beneath the Ross Ice Shelf have been low, particularly under shallow ice drafts, leading to overall thickening and increased buttressing potential. The team aims to provide a direct estimate of basal melt rates based on changes in ice-shelf thickness that occurred between 1971 and 2017. This project will extend similar work completed at Thwaites Glacier and improve the calibration methods on the vertical scaling for fast-time and depth conversion. The work will also leverage the dense modern surveys to improve the geolocation of radar film collected on earlier field campaigns to produce a more precise comparison of local shelf thickness with the modern data. In addition, the team will conduct englacial attenuation analysis to calculate englacial temperature to infer the trends in local basal melting. They will also examine the radiometric and scatterometric character of bed echoes at the ice-ocean boundary to characterize changes in ice-shelf basal roughness, marine-ice formation related to local basal freezing, and structural damage from fracture processes.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.