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

观测表明，在格陵兰冰盖西坡上，几年来夏季冰速度的增加与融水产量的增加之间存在关系。这个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（纬度约为北纬70度）内绘制冰穴（将地表融水输送到冰盖床上的垂直管道）的空间分布图。这位博士生将把观测到的moulin位置与基于1985年航空摄影的地形图上确定的历史moulin位置进行比较，以确定moulin分布随时间的变化。将推导出一个多元回归模型来解释整个研究区域的moulin密度。由冰穴密度确定的冰下水压将利用先前在高山冰川中验证过的滑动规律转化为基本滑动速度。然后，在当前和未来的气候条件下，将使用一个耦合的热力学冰盖模型模拟季节性融化加速现象，后者包括模拟的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。该项目的第二个目标是确定冰穴分布随时间的变化。将通过高分辨率（大约一米像素）商业卫星图像的特征提取来确定冰穴分布。海平面上升是一个高度相关的社会问题。目前对冰川和冰盖对海平面上升贡献的估计主要基于表面质量平衡，忽略了冰速变化的可能影响，其中冰损增加与冰山崩解增加有关。因此，该项目将直接解决提高对格陵兰冰盖冰流加速可能导致海平面上升的基本认识的需要。该项目的产品将是研究区域内的冰穴密度和基底滑动的大小和空间分布的地图。该项目将提供关于融水对冰盖冰动力的影响的新见解，通过提供新的表面水文模型（即moulin密度）以及基底滑动（冰下水压与冰基岩界面冰速度之间的关系）。在这个项目中所取得的参数化和概念上的进步也可能对高山冰川群落有用。该项目将应用这些理论进展来探索格陵兰冰盖西侧翼冰面速度与夏季融化持续时间之间观测到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.