Seasonal flow variability as an indicator of mountain glacier basal conditions

季节性流量变率作为山地冰川基础条件的指标领导：Duncan Quincey （University of Leeds）联合指导：Francesca Pellicciotti (WSL), John Elliott (Leeds), Noel Gourmelen （Edinburgh）冰川热状态，特别是河床融水的存在或缺失，是冰下过程的关键控制因素。它控制着沉积物侵蚀、携带和搬运的速率，地下水文网络的性质，以及冰川流动的模式和速率。有证据表明，即使在高海拔地区，气温上升也在影响冰川和冰下的热条件4，这意味着在未来变暖的世界中，多热和温带冰条件将变得更加普遍。因此，能够描述冰川基本条件及其变化的特征，对于预测景观演变、融水储存和输送、冰川流量以及最终预测冰川衰变至关重要。考虑到对冰下条件的直接观察仅限于局部暴露或洞穴调查，作为冰下水储存的代表的遥感方法对山地冰川学家来说将是一个有用的工具。先前的工作2,3表明，冰川流速的季节性变化可以指示与冰川滑动相关的冰下储水量，因此也可以指示温带冰（图1）。图1：喀喇昆仑Baltoro冰川（左）及其年平均中线速度。季节速度（右）表明在海拔较高的地方有温暖的冰，因为剖面在距离终点约10公里处偏离。因此，该博士项目将通过初步得出具有已知热特征的山地冰川的季节性流速数据，来描述流量的空间模式及其随时间的变化，从而寻求测试和扩展这一假设。它将建立在监督小组之前的工作基础上，主要利用图像特征跟踪和雷达干涉测量进行定制速度分析，并辅以ITS_LIVE等现有存储库中的免费数据集。它将探索一系列天基SAR（例如Sentinel-1）和光学（例如Planet）图像，以及现成和定制的数字高程数据集，并将开发现有的和派生新的自动化处理工作流程例程。后续步骤将吸收由模拟气候、冰厚和能量平衡数据支持的加速/减速区域数据集，以推断更广泛的冰下条件。还有机会根据成功申请者的兴趣/技能，使用微型dgps收集补充性的现场速度数据。参考文献，cook等，（2020）10.1038/s41467-020-14583-8。2. Benn等，（2017）10.5194/tc-11-2247-2017。3. Quincey等人，（2009）10.3189/002214309790794913。4. 张志强，张志强等，（2020）10.5194/tc-14-925-2020。5. Temminghoff等人，（2018）10.1080/04353676.2018.1545120。

Seasonal flow variability as an indicator of mountain glacier basal conditionsLead supervisor: Duncan Quincey (University of Leeds)Co-supervisors: Francesca Pellicciotti (WSL), John Elliott (Leeds), Noel Gourmelen (Edinburgh)Glacier thermal regime, and in particular the presence or absence of meltwater at the bed, is a key control of subglacial processes. It governs rates of sediment erosion, entrainment and transport1, the nature of subsurface hydrological networks2, and patterns and rates of glacier flow3. Evidence suggests that rising air temperatures are influencing englacial and subglacial thermal conditions even at high-altitude4, meaning that in a future warming world polythermal and temperate ice conditions will become more widespread. Being able to characterise glacier basal conditions, and how they change, will therefore be critical for predicting landscape evolution, meltwater storage and conveyance, glacier discharge, and ultimately for forecasting glacier decay.Given that direct observations of subglacial conditions are limited to localised exposures or speleological investigations5, a remote sensing approach that serves as a proxy for subglacial water storage would be a useful tool for mountain glaciologists. Previous work2,3 has suggested that seasonal changes in glacier velocity can indicate subglacial water storage, associated with glacier sliding, and therefore temperate ice (Figure 1).Figure 1: The Baltoro Glacier, Karakoram (left), and its annually averaged centreline velocity. Seasonal velocities (right) indicating warm ice at higher elevations as the profiles diverge at ~10 km from the terminus.This PhD project will therefore seek to test and expand this hypothesis, by initially deriving seasonal velocity data for mountain glaciers with known thermal characteristics, to describe spatial patterns of flow, and their change through time. It will build on previous work from within the supervisory group, primarily making use of image feature tracking and radar interferometry for bespoke velocity analyses, supplemented by freely available datasets from existing repositories such as ITS_LIVE. It will explore a range of space-based SAR (e.g. Sentinel-1) and optical (e.g. Planet) imagery, as well as off-the-shelf and custom-built digital elevation datasets, and will develop existing and derive new routines for automating processing workflows. Subsequent steps will assimilate regional datasets of speed-up/slow-down, supported by modelled climate, ice thickness and energy balance data, to infer broader subglacial conditions. There is also the opportunity to collect complementary field-based velocity data, using micro-dgps, depending on the interests/skills of the successful applicant.ReferencesCook et al., (2020) 10.1038/s41467-020-14583-8. 2. Benn et al., (2017) 10.5194/tc-11-2247-2017. 3. Quincey et al., (2009) 10.3189/002214309790794913. 4. Vincent, C. et al., (2020) 10.5194/tc-14-925-2020. 5. Temminghoff et al., (2018) 10.1080/04353676.2018.1545120.