Controls on short-term calving glacier dynamics

山脉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据可查的后果，对下游水文和淡水供应以及海平面上升都有影响。在最近冰量减少的同时，在许多冰川末端观察到的冰川湖泊在数量和面积上都有所增加，因为冰川过深变得不结冰并充满了融水。这种湖泊的大小和数量预计在未来将会增加。已经观察到冰缘湖泊的存在通过一些热机械过程和正反馈改变了冰川的动态和行为。虽然崩解通量主要是冰速的函数，但冰川边缘退缩到越来越深的水中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脱钩，因为湖泊吸收热量以及水温、水深和环流模式的季节性波动影响着冰川的崩解状况。遥感数据表明，终止于湖泊的冰川的流动速度和消退速度大大快于附近的终止于陆地的冰川。这些变化提供了对局部尺度上的烧蚀机制的洞察，由于难以在必要的时间和空间尺度上获取数据，迄今在质量平衡和表面能量模型中对这些机制的量化很差。事实上，尽管对整个冰川质量损失作出了这些重要贡献，但记录和量化终止湖泊的冰川和冰盖的“锋面消融”(包括崩解、水下和空中锋面融化)的现场数据很少。实地传感器和监测/调查技术的进步，加上遥感平台的发展，在数据的数量、质量和可获得性方面产生了阶段性的变化。这些进展为在嵌套的空间和时间尺度范围内更好地理解冰川锋面消融的速度、控制和机制开辟了新的机会(在山区冰川和冰盖演化的数值模型中迫切需要这些数据)。该项目的目的是限制冰川崩解成冰缘湖泊的短期动态。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、短期重复的动态结构(SfM)冰川调查将由包裹船、船或无人驾驶飞行器(UAV)进行，并将提供有关冰解量、时间和机制的信息。气象站、跟踪摄像机以及压力传感器和热敏电阻串组成的网络将提供有关天气和湖泊条件的信息。最终的现场地点(S)将与任何成功的候选人讨论。项目组在包括喜马拉雅山脉、西格陵兰、北极瑞典和新西兰在内的一系列实地地点都有解决这些问题的既定历史和经验。由于这种冰川湖泊的后勤优势和数量，我们预计将在冰岛瓦特纳约库冰帽的出口冰川上进行初步实地工作。目标：(1)在一个地点收集一个季节/一年的环境/湖泊数据的同时，密切监测冰川崩解过程；(2)对该地点(或附近多个地点)的表面融化和崩解体积之间的质量损失进行划分；(3)通过更广泛的光接触监测活动/对其他数据源的分析和对较长期遥感数据档案的分析，确定对这种质量损失划分的控制。

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.