NSFGEO-NERC: Two-phase dynamics of temperate ice

从南极冰盖的冰的排放是由冰流流动，但没有共识，是什么控制的开始和冰流的几何形状或它们的演变。不同的观察清楚地表明，水在影响流动阻力的重要性，无论是在冰缘和在床上。然而，冰流模型还没有考虑到必要的温度，含水量和冰变形之间的反馈，以解决和询问这些过程。具体的观测突出了各种过程和知识差距：㈠冰流的基底水文造成了低基底剪切应力，使应力和应变集中在冰流边缘; ㈡冰流剪切边缘内的应变加热使冰的温度升高到压力熔点，造成内部耗散性融化，有助于控制温带冰的分布;（iii）冰流边缘的间隙水可能会显著软化冰，但动力学后果知之甚少;（iv）冰流变学对含水量的依赖性本身受到的限制很小;（v）温带冰的多相动力学，包括冰盖内的渗透率和排水率，尚不清楚;（vi）融水流向冰床和在冰床处的路线是对冰速的主要控制。如果没有解决这些过程的模型，冰盖的质量平衡和海平面贡献的预测将不可避免地是投机性的，没有完整的物理基础。这项研究将针对温带冰的动态，其首要目标是确定其对冰流的影响。该项目将有两个相互加强的组成部分：实验室实验，其中将使用爱荷华州州立大学现有的旋转装置来研究含水量对温带冰的流变性和渗透性的影响;牛津大学发展了一个两阶段的热力学理论，用于温带冰流--水的产生，储存，和路由-这将服务于冰流运动的完全动态和多维模型的基础。实验结果将指导本构规则和参数范围考虑的理论，和应用的理论元素将改善实验结果的解释。该理论和由此产生的模型将预测温带冰，水，应力，变形和基底滑移的耦合分布，控制冰流速度和几何形状的演变。

Discharge of ice from the Antarctic Ice Sheet is dominated by ice-stream flow, but there is no consensus as to what controls the onset and geometry of ice streams or their evolution. Diverse observations clearly indicate the importance of water in affecting flow resistance, both within the icestream margins and at the bed. However, ice-stream models do not yet account for the necessary feedbacks among temperature, water content, and ice deformation to resolve and interrogate these processes. Specific observations highlight processes and knowledge gaps: (i) the basal hydrology of ice streams is responsible for low basal shear stresses that focus stress and strain at ice-stream margins; (ii) strain heating within ice-stream shear margins raises the temperature of the ice to the pressure melting point, causing internal dissipative melting and helping to control the distribution of temperate ice; (iii) interstitial water in ice-stream margins may significantly soften the ice, with poorly known dynamical consequences; (iv) the dependence of ice rheology on water content is itself poorly constrained; (v) the multiphase dynamics of temperate ice, including permeability and drainage rates within ice sheets, are not known; (vi) routing of meltwater to and at the bed is a primary control on ice speed. Without models that address these processes, predictions of the ice sheet's mass balance and sea-level contribution will inevitably be speculative, with incomplete physical grounding.This study will target the dynamics of temperate ice, with the overarching goal of determining its effect on ice streaming. The project will have two components that reinforce each other: laboratory experiments in which an existing rotary device at Iowa State University will be used to study the effect of water content on the rheology and permeability of temperate ice; and development at Oxford University of a two-phase, thermo-mechanical theory for temperate ice flow-with water production, storage, and routing-that will serve at the basis for fully dynamic and multidimensional models of ice-stream motion. Results of the experiments will guide the constitutive rules and parameter ranges considered in the theory, and application of elements of the theory will improve interpretations of the experimental results. The theory and resultant models will predict the coupled distributions of temperate ice, water, stress, deformation, and basal slip that control the evolution of ice-stream speed and geometry.