Doctoral Dissertation Research: Modeling the Influence of Surface Meltwater on the Ice Dynamics of the Greenland Ice Sheet

观测表明，在格陵兰冰盖的西坡上，夏季冰速的增加与几年来融化水产量的增加之间存在着关系。这一博士论文研究项目将根据高分辨率卫星图像，在西格陵兰岛雅各布港/伊卢利萨特东北1100平方公里的内陆冰区域(北纬约70度)内绘制Moulins(将表面融化的水输送到冰盖床的垂直管道)的空间分布图。博士生将把观测到的磨坊位置与1985年航空摄影地形图上确定的历史磨坊位置进行比较，以确定磨坊分布随时间的变化。将得到一个多元回归模型来解释整个研究区域的摩林密度。根据冰川密度确定的冰下水压将转化为基础滑动速度，使用之前验证过的高山冰川滑动定律。然后，将在现在和未来的气候条件下使用耦合热力学冰盖模型来模拟季节性融化加速现象，后者包括模拟地表融水产量的增加。该项目的主要目标是模拟观测到的融化引起的冰流加速的物理基础，并预测这一机制将如何影响未来的冰盖动力学。该项目的次要目标是确定Moulin分布随时间的变化。Moulin分布将通过从高分辨率(大约一米像素)的商业卫星图像中提取特征来确定。海平面上升是一个高度相关的社会问题。目前估计的冰川和冰盖对海平面上升的贡献主要基于表面物质平衡，忽略了冰速变化的可能影响，冰山崩解增加导致冰损失增加。因此，该项目将直接解决增进对格陵兰冰盖中冰流加速可能导致的海平面上升贡献的基本了解的需要。该项目的产品将是研究区域内冰川密度以及基岩滑坡的规模和空间分布的地图。该项目将提供关于融化水对冰盖冰动力学影响的新见解，通过贡献新的地表水文学模型(即莫林密度)和基底面滑动(冰层下水压力和冰基岩界面处的冰速度之间的关系)。该项目所取得的参数和概念上的进展可能也将对高山冰川社区有用。该项目将应用这些理论进展来探索观测到的格陵兰冰盖西侧冰面速度与夏季融化持续时间之间的相关性的物理基础。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。

Observations have shown a relationship between increased summer ice velocity and increased meltwater production over several years on the western slope of the Greenland Ice Sheet. This doctoral dissertation research project will map the spatial distribution of moulins (vertical conduits that transmit surface meltwater to the bed of the ice sheet) based on high-resolution satellite imagery within a 1,100 square-km area of the inland ice northeast of Jakobshavn/Ilulissat, West Greenland (at a latitude of roughly 70-degrees N). The doctoral student will compare observed moulin locations to historical moulin locations as identified on a topographical map based on 1985 aerial photography in order to identify changes in moulin distribution over time. A multivariate regression model will be derived to explain moulin density across the study area. Subglacial water pressures, determined from moulin density, will be translated into basal sliding speed using sliding laws previously validated for alpine glaciers. The seasonal melt-acceleration phenomenon then will be modeled using a coupled thermodynamic ice sheet model under both present day and future climatic conditions, with the latter including a simulated increase in surface meltwater production. The primary goal of this project is to model the physical basis of the observed melt-induced acceleration of ice flow and predict how this mechanism will influence ice sheet dynamics in the future. The secondary goal of the project is to identify changes in moulin distribution over time. Moulin distribution will be determined via feature extraction from high resolution (with roughly one meter pixels) commercial satellite imagery.Sea-level rise is a highly relevant societal concern. The estimated sea-level rise contribution from glaciers and ice sheets currently is based primarily on surface mass balance and ignores the possible influence of changing ice velocity, with increased ice loss related to increased iceberg calving. This project therefore will directly address the need to improve basic understanding of the potential sea-level rise contribution due to accelerated ice flow in the Greenland Ice Sheet. The products of this project will be maps of moulin density and of the magnitude and spatial distribution of basal slide within the study area. This project will provide new insights regarding the influence of meltwater on the ice dynamics of ice sheets by contributing novel models of surface hydrology (i.e moulin density) as well as basal slide (the relation between subglacial water pressure and ice velocity at the ice-bedrock interface). The parameterizations and conceptual advances made in this project likely will be useful for the alpine glacier community as well. This project will apply these theoretical advances to probe the physical basis of the observed correlation between ice surface velocity and duration of summer melt on the western flank of the Greenland Ice Sheet. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.