NSFGEO-NERC: Two-phase dynamics of temperate ice

南极冰盖的冰的排放主要是冰流的流动，但对于是什么控制了冰流的开始和几何形状或它们的演变，还没有达成共识。不同的观测结果清楚地表明水在影响冰流边缘和河床的流动阻力方面的重要性。然而，冰流模型尚未考虑到温度、含水量和冰变形之间的必要反馈，以解决和询问这些过程。具体的观测结果突出了过程和知识差距：(i)冰流的基础水文是造成低基底剪应力的原因，这种剪应力和应变集中在冰流边缘；（ii）冰流切变边缘的应变加热使冰的温度升高到压力熔点，引起内部耗散融化，有助于控制温带冰的分布；（iii）冰流边缘的间隙水可能显著软化冰，其动力学后果鲜为人知；（iv）冰流变学对含水量的依赖性本身约束较差；(v)温带冰的多相动力学，包括冰盖内的渗透率和排水率，是未知的；（六）融水流向和流向河床是对冰速的主要控制。如果没有解决这些过程的模型，对冰盖质量平衡和海平面贡献的预测将不可避免地是推测性的，没有完整的物理基础。这项研究将以温带冰的动力学为目标，以确定其对冰流的影响为总体目标。该项目将有两个相互加强的组成部分：实验室实验，其中爱荷华州立大学现有的旋转装置将用于研究含水量对温带冰的流变学和渗透性的影响；牛津大学的两阶段热力学理论研究——包括水的产生、储存和输送——将成为冰流运动的全动态和多维模型的基础。实验结果将指导理论中考虑的本构规则和参数范围，理论元素的应用将改进对实验结果的解释。理论和由此产生的模型将预测控制冰流速度和几何演变的温带冰、水、应力、变形和基底滑移的耦合分布。

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.