Controls on short-term calving glacier dynamics

山地冰川和冰盖边缘的全球退缩和变薄是最近气候变化的一个有充分记录的后果，影响下游的水文和淡水供应以及海平面上升。随着最近冰量的减少，在许多冰川末端观测到的原冰期湖泊在数量和面积上都有所增加，因为冰川过深变得无冰并充满融水。这类湖泊的规模和数量预计在未来还会增加。已经观察到冰缘湖的存在通过一些热机械过程和正反馈改变了冰川的动力学和行为。虽然产冰通量主要是冰速的函数，但冰川边缘的退缩逐渐进入更深的水会改变冰川的纵向应力分布。此外，湖泊本身可以将冰川质量损失与气候强迫分离，因为湖泊的吸热以及水温、深度和环流模式的季节性波动都会影响产冰状态。遥感数据表明，湖泊末端冰川的流速和退缩要比附近陆地末端冰川快得多。这些变化提供了对局部尺度烧蚀机制的深入了解，迄今为止，由于难以获得必要的时空尺度数据，在质量平衡和表面能量模型中很少量化烧蚀机制。事实上，尽管这些对总体冰川质量损失有重要贡献，但很少有记录和量化湖泊末端冰川和冰盖的“锋面消融”（包括裂冰、水下和陆上锋面融化）的实地数据。现场传感器和监测/调查技术的进步，加上遥感平台的发展，使数据的数量、质量和可得性发生了逐步变化。这些进展为在空间和时间尺度的嵌套范围内更好地理解冰川锋面消融的速率、控制和机制开辟了新的机会。这些数据迫切需要在山地冰川和冰盖演化的数值模型中更好地代表湖-冰川相互作用。该项目的目的是限制冰川崩解成冰边缘湖的短期动态。将部署一系列新的现场监测技术，作为数据采集的一部分。高分辨率、短期重复的运动结构（SfM）冰川调查将由木筏、船只或无人驾驶飞行器（UAV）进行，以提供有关产冰量、时间和机制的信息。气象站、跟踪摄像机、压力传感器网络和热敏电阻串将提供有关天气和湖泊状况的信息。最终的场地将在与任何成功的候选人讨论后选择。项目团队在喜马拉雅山脉、西格陵兰岛、瑞典北极和新西兰等一系列现场研究这些问题方面有着悠久的历史和经验。由于后勤方面的优势和此类前冰期湖泊的数量，我们预计将在冰岛Vatnajökull冰帽的出口冰川上进行初步的实地考察。此外，在这个地点有潜在的机会来检查大规模的碎片添加到冰川表面对监测关系的影响。目标(1)在一个地点收集一个季节/年的环境/湖泊数据的同时，密切监测冰川崩解过程；(2)将该站点（或附近多个站点）的表面熔体和崩解体积之间的质量损失进行分配；(3)通过更广泛的轻触监测活动/对其他数据源的分析和对长期遥感数据档案的分析，确定对质量损失分区的控制。

The global retreat and thinning of mountain glaciers and ice sheet margins is a well-documented consequence of recent climate changes, impacting both downstream hydrology and freshwater availability and eustatic sea-level rise. Alongside recent reductions in ice volume, proglacial lakes observed at the termini of many glaciers have increased in both number and areal extent as glacier overdeepenings become ice-free and fill with meltwater. The size and number of such lakes is projected to increase in future.The presence of an ice-marginal lake has been observed to change the dynamics and behaviour of a glacier via a number of thermo-mechanical processes and positive feedbacks. While calving fluxes are mostly a function of ice velocity, the retreat of a glacier margin into progressively deeper water alters the longitudinal stress distribution of a glacier. Moreover, the lake itself can decouple glacier mass loss from climate forcing as heat absorption by the lake and seasonal fluctuations in water temperature, depth and circulation patterns influence the calving regime Remote sensing data indicates that the flow velocity and retreat of lake-terminating glaciers is substantially faster than nearby land-terminating glaciers. These changes provide an insight into ablation mechanisms at a local scale that have hitherto been poorly quantified in mass balance and surface energy models because of the difficulty of acquiring data at the necessary temporal and spatial scale. Indeed, despite these important contributions to overall glacier mass loss, there is a paucity of field data documenting and quantifying "frontal ablation" (including calving, subaqueous and subaerial frontal melt) of lake-terminating glaciers and ice sheets. Advances in field sensors and monitoring/survey techniques, coupled with developments in remote sensing platforms have created a step-change in the quantity, quality and availability of data. Such advances have opened up new opportunities to better understand the rates, controls and mechanisms of glacier frontal ablation at a nested range of space and time scales These data are urgently needed to better represent lake-glacier interactions in numerical models of mountain glacier and ice sheet evolution). The aim of this project is to constrain the short-term dynamics of glaciers calving into ice marginal lakes. An array of novel field monitoring techniques will be deployed as part of data acquisition. High resolution, short-term repeat Structure-from-Motion (SfM) glacier surveys will be undertaken from a packraft, boat or Uncrewed Aerial Vehicle (UAV) and differenced to provide information on calving volumes, timing and mechanisms. A weather station, trail cameras and networks of pressure sensors and thermistor strings will provide information on weather and lake conditions.The final field site(s) will be chosen in discussion with any successful candidate. The project team have an established history and experience of working on these questions at a range of field sites including the Himalayas, West Greenland, Arctic Sweden and New Zealand. Owing to the logistical advantages and number of such proglacial lakes, we anticipate initial fieldwork to be conducted on outlet glaciers of the Vatnajökull Ice Cap, Iceland. Moreover, at this site there is the potential opportunity to examine the impact of large-scale additions of debris onto the glacier surface on the monitored relationships.Objectives(1) To intensely monitor glacier calving processes alongside environmental/lake data collection at one site for a season/year;(2) To partition mass loss between surface melt and calving volumes at that site (or multiple sites nearby);(3) To determine the controls on that mass loss partition from a wider light touch monitoring campaign/analyses of other data sources and analysis of the longer-term remote sensing data archive.