Seasonal flow variability as an indicator of mountain glacier basal conditions

作为山地冰川基本条件指标的季节性流量变化领导主管：Duncan Quincey(利兹大学)共同主管：Francesca Pellicciotti(WSL)，John Elliott(利兹)，Noel Gourmelen(爱丁堡)冰川热状况，特别是床上是否有融水，是冰下过程的关键控制因素。它控制着泥沙侵蚀、夹带和输送的速度1、地下水文网络的性质2以及冰川流动的模式和速度3。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状况4，这意味着在未来变暖的世界中，多热和温带冰川状况将变得更加普遍。因此，能够描述冰川基本条件及其变化的特征，对于预测地貌演变、融水储存和输送、冰川排放以及最终预测冰川消亡至关重要。鉴于对冰川下条件的直接观察仅限于局部暴露或洞穴调查5，作为冰下水储存的替代方法的遥感方法将是山区冰川学家的有用工具。以前的工作2，3表明，冰川速度的季节变化可以表明冰川下的水储存，与冰川滑动有关，因此是温和的冰(图1)。图1：喀喇昆仑的巴尔托罗冰川(左)，以及它的年平均中心线速度。季节速度(右)表示高海拔地区的温暖冰层，因为冰面偏离终点处约10公里。因此，该博士项目将寻求验证和扩展这一假设，通过初步获得具有已知热特征的山地冰川的季节速度数据，以描述流动的空间模式及其随时间的变化。它将建立在监督小组以前的工作基础上，主要利用图像特征跟踪和雷达干涉测量进行定制的速度分析，并辅之以来自现有储存库(如ITS_LIVE)的免费提供的数据集。它将探索一系列天基合成孔径雷达(例如哨兵1号)和光学(例如行星)图像，以及现成的和定制的数字高程数据集，并将开发现有的和派生出自动化处理工作流程的新例程。后续步骤将在模拟的气候、冰层厚度和能量平衡数据的支持下，吸收加速/减速的区域数据集，以推断更广泛的冰下条件。根据成功申请者的兴趣/技能，还有机会使用微型差动全球定位系统收集补充的现场速度数据。2.本等人，(2017年)10.5194/TC-11-2247-2017年。3.昆西等人，(2009年)10.3189/002214309790794913。4.文森特等人，(2020年)10.5194/TC-14-925-2020年。5.特明霍夫等人，(2018年)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.