Hydraulic Permeability of Temperate Ice

水调节着影响海平面上升的海洋冰川和冰流的快速流动。具体地说，冰川在快速流动的冰边缘深处的流动，那里的冰接近其压力熔点，取决于储存在冰粒边界处的矿脉网络中的液态水的比例。因此，了解这些系统的渗透性是至关重要的。该项目的目标是通过对实验室冰和冰川冰的测试，更好地了解对冰渗透性的控制。实验室冰的实验将揭示颗粒大小和水含量如何影响渗透率，而冰川冰的实验将研究冰的变形如何影响渗透率。这些实验的结果将使人们更好地了解冰在压力熔点附近的渗透率随颗粒大小、水分含量和变形的变化。这些实验并不是为了模拟冰川中的间隙水流动。该项目包括研究生和本科生的参与，旨在包括PolarTREC项目的一名参与者，让学生在K-12课堂上参与。该项目将首次测量温带冰的渗透率，作为其颗粒大小、水分含量和叶化的函数。该团队将使用为这一应用而设计和测试的落水头渗透仪。直径140毫米、厚度达70毫米的冰盘被保持在压力和压力融化温度下，而冷水在允许随时间减少的磁头下瞬时流过磁盘。水头下降率提供了渗透率值。不同的水含量将通过改变冰的盐度来获得，并将使用在先前的冰变形实验中成功使用的量热方法来测量。引入冰盘的冷水将含有荧光素染料，以便在实验后对流动网络进行薄层研究。用从阿尔伯塔省阿萨巴斯卡冰川浅岩心采集的冰川冰进行实验，将评估冰叶类型和方向对渗透性的影响。这些测量还可能指出实验室制造的冰和冰川冰的渗透率之间的差异，这些差异与结构的各向异性无关。这些实验的结果将为基于水在理想静脉网络中的Poiseuille流动的渗透率模型提供第一次测试。这些未经检验的模型是估计冰川流动模型中冰渗透率的主要基础。该项目产生的新的基于经验的渗透率模型将允许估计冰流剪切边缘温带部分的水分含量，从而改进剪切边缘中水软化冰的模型和相关的冰流运动学。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Water regulates the fast flow of marine-terminating glaciers and ice streams that affect sea-level rise. Specifically, the flow of glacial ice at depth in the margins of fast-flowing ice, where the ice is near its pressure melting point, depends on the fraction of liquid water stored in the network of veins at ice-grain boundaries. It is therefore critical to understand the permeability of these systems. The goal of this project is to better understand controls on ice permeability through tests on laboratory ice and glacier ice. Experiments with laboratory ice will inform on how grain size and water content affect permeability, while experiments with glacier ice will examine how deformation of the ice affects permeability. Results of these experiments will provide a better understanding of permeability of ice near its pressure melting point as a function of grain size, water content, and deformation. The experiments are not intended to simulate interstitial water flow in a glacier. This project includes graduate and undergraduate participation and seeks to include a participant from the PolarTREC program to engage students in K-12 classrooms.This project will measure for the first time the permeability of temperate ice as a function of its grain size, water content, and foliation. The team will use a falling-head permeameter designed and tested for this application. A disk of ice, 140 mm in diameter and up to 70 mm thick, is kept under pressure and at the pressure-melting temperature while chilled water transiently flows through the disk under a head that is allowed to decrease with time. The rate of head decrease provides the permeability value. Different water contents will be achieved by varying the salinity of the ice and will be measured with a calorimetric method used successfully in prior ice-deformation experiments. Chilled water introduced to ice disks will contain fluorescein dye to allow flow networks to be studied in thin-sections after experiments. Experiments with glacier ice, collected from shallow cores at Athabasca Glacier, Alberta, will evaluate the effect of ice foliation style and orientation on permeability. These measurements may also point to differences between permeability of lab-made and glacier ice that are unrelated to structural anisotropy. Results of these experiments will provide the first test of permeability models based on Poiseuille flow of water though idealized vein networks. These untested models are the primary basis for estimating ice permeability in glacier flow models. New empirically-grounded permeability models resulting from this project will allow the water content of temperate portions of ice-stream shear margins to be estimated, thereby improving models of ice softening by water and associated ice-flow kinematics in shear margins.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.