The response of marine-terminating outlet glaciers in northwestern Greenland to recent and near-future climate change

自20世纪90年代以来，格陵兰冰盖的质量损失不断增加，导致1992年至2018年全球海平面估计上升10.80.9毫米。质量损失的发生是由于海冰出口冰川的冰锋的表面融化增加和冰流量增加，这些冰川是快速流动的冰传送带，使冰盖流失。预计到2100年，北极气温将上升8摄氏度，这可能会进一步增加海运出口冰川的冰排放量，并在不久的将来显著导致海平面上升。然而，我们对控制冰流量的因素的认识还存在根本性的差距。21世纪初，冰流量的增加最初集中在格陵兰岛东南部。然而，自2005年以来，西北地区终止海洋的出口冰川的冰量开始加速排放，整个地区都在迅速加速、退缩和变薄。尽管如此，只有数量有限的区域研究，其中许多在空间和/或时间上受到限制，在格陵兰西北部进行了研究，以了解控制其最近动态变化的机制，对冰川行为的次年际变化的研究尤其不足。因此，目前冰川行为的变化在多大程度上是由大气和海洋强迫造成的，还是冰川床地形等冰川特有因素造成的，目前仍不清楚。该项目旨在利用遥感数据扩展以往的研究（如Carr et al. 2013b; Moon et al. 2015），在空间和时间上评估格陵兰西北部海洋终端出口冰川的终端位置、速度和地表高程的近期季节性变化，并确定控制其近期和近期行为的机制。它将解决以下研究问题：1。格陵兰西北海域出入口冰川的季节终点位置、速度和地表高度是如何演变的？它们在空间上是如何变化的？海冰在多大程度上控制着入海出海口冰川的动态，而这又如何随着峡湾形态和海冰特征的不同而变化？格陵兰岛西北部冰川的季节性速度模式是什么？它们的主要控制因素是什么？未来格陵兰岛西北部的冰川会如何变化？它们的基底地形会在多大程度上影响冰川的变化？为了解决这些问题，将从测量项目中获得季节性冰川速度，以评估冰速度的变化，将使用高分辨率Landsat 8和Sentinel-2卫星图像来测量终端位置的变化，并获取ICESat和北极DEM数据来评估地表高程变化。海冰和冰架（弱季节性冰架）对季节性冰川动态的影响将通过美国国家冰中心图表和从卫星图像中对冰川末端的海冰/冰架的刚性进行分类来检查。在此之后，将分析RACMO2.3p2和季节终点位置的地表径流测量值，以确定它们对整个地区季节性冰川速度的影响。在项目的最后阶段，将使用Úa有限元素冰流模型来评估海洋终端出口冰川未来对气候变化的敏感性，重点关注基底地形的影响。总体而言，该项目旨在进一步科学理解格陵兰岛西北部的海洋终端出口冰川如何应对最近的气候变化，确定哪些强迫机制主要控制它们的行为，并估计该地区的冰川如何应对近期的气候变化。

Summary of proposed projectThe Greenland Ice Sheet has experienced increased mass loss since the 1990s, resulting in an estimated global sea level rise of 10.8 0.9 mm from 1992-2018. Mass loss has occurred through increased surface melting and enhanced ice discharge at the ice-fronts of marine-terminating outlet glaciers, which are fast-flowing conveyor belts of ice that drain the ice sheet. Arctic air temperatures are projected to rise by up to 8 C by 2100, which are likely to further increase ice discharge from marine-terminating outlet glaciers and contribute significantly to near-future sea level rise. Nevertheless, there are fundamental gaps in our understanding of the factors controlling ice discharge. Increases in ice discharge were initially concentrated in southeastern Greenland during the early 2000s. However, since 2005 accelerated ice discharge from marine-terminating outlet glaciers has begun in the northwest, with rapid acceleration, retreat and thinning occurring throughout the region. Despite this, only a limited number of regional studies, many of which have been spatially and/or temporally constrained, have been conducted in northwestern Greenland to understand the mechanisms controlling its recent dynamic change, with sub-annual variations in glacier behaviour particularly understudied. Therefore, the extent to which current changes in glacier behaviour are being forced by atmospheric and oceanic forcing or are the result of glacier-specific factors such as the topography of the glacier bed remains unclear. This project aims to use remotely sensed data to extend previous studies (e.g. Carr et al. 2013b; Moon et al. 2015) spatially and temporally to assess recent seasonal changes in terminus position, velocity and surface elevation at marine-terminating outlet glaciers in northwestern Greenland and determine the mechanisms controlling their recent and near-future behaviour. It will address the following research questions:1. How have the seasonal terminus positions, velocities and surface elevations of marine-terminating outlet glaciers in northwestern Greenland evolved and how does this vary spatially?2. To what extent does sea ice control marine-terminating outlet glaciers dynamics, and how does this vary with the different fjord configurations and sea ice characteristics?3. What are the seasonal velocity patterns of northwestern Greenland's glaciers, and what are their primary controls?4. How might northwest Greenland glaciers behave in the future, and to what extent could this be influenced by their basal topography?To address these questions, seasonal glacier velocities will be obtained from the MEaSUREs Project to assess changes in ice velocity, high resolution Landsat 8 and Sentinel-2 satellite imagery will be used to measure variations in terminus position, and ICESat and Arctic DEM data will be acquired to assess surface elevation changes. The influence of sea ice and ice mélange (weak seasonal ice shelf) upon seasonal glacier dynamics will be examined from US National Ice Centre Charts and by categorising the rigidity of sea ice/ice mélange at the glacier termini from satellite imagery. Following this, surface runoff measurements from RACMO2.3p2 and seasonal terminus positions will be analysed to determine their influence upon seasonal glacier velocities throughout the region. In the final stages of the project, the Úa finite-elemental ice-flow model will be used to assess the future sensitivity of marine-terminating outlet glaciers to climate change, with focus given to the influence of basal topography. Overall, this project seeks to further the scientific understanding on how northwestern Greenland's marine-terminating outlet glaciers have responded to recent climate change, determine which forcing mechanisms are primarily controlling their behaviour and estimate how the region's glaciers may respond to near-future climate change.