The Relevance of Grain Dissection for Grain Size Reduction in Polar Ice: Insights from Numerical Models and Ice Core Microstructure Analysis

Frontiers in Digital Humanities

Pennock, Gill M.¹  Eichler, Jan¹  Drury, Martyn R.³  Steinbach, Florian³  Weikusat, Ilka³  Bons, Paul D.⁴  Kuiper, Ernst-Jan N.⁵  Griera, Albert⁵ 

[1] Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Germany;Departament de Geologia, Universitat AutòDepartment of Geosciences, Eberhard Karls University TüDepartment of Geosciences, Utrecht University, Netherlands;bingen, Germany;noma de Barcelona, Spain

关键词: Ice microstructure modelling;    cryo-EBSD;    Fabric analyser;    Ice deformation;    Dynamic recrystallisation;    Grain size evolution;    grain dissection;    NEEM ice core;   

DOI  :  10.3389/feart.2017.00066

学科分类：社会科学、人文和艺术（综合）

来源: Frontiers

【 摘 要 】

The flow of ice depends on the properties of the aggregate of individual ice crystals, such as grain size or lattice orientation distributions. Therefore, an understanding of the processes controlling ice micro-dynamics is needed to ultimately develop a physically based macroscopic ice flow law. We investigated the relevance of the process of grain dissection as a grain-size-modifying process in natural ice. For that purpose, we performed numerical multi-process microstructure modelling and analysed microstructure and crystallographic orientation maps from natural deep ice-core samples from the North Greenland Eemian Ice Drilling (NEEM) project. Full crystallographic orientations measured by electron backscatter diffraction (EBSD) have been used together with c-axis orientations using an optical technique (Fabric Analyser). Grain dissection is a feature of strain-induced grain boundary migration. During grain dissection, grain boundaries bulge into a neighbouring grain in an area of high dislocation energy and merge with the opposite grain boundary. This splits the high dislocation-energy grain into two parts, effectively decreasing the local grain size. Currently, grain size reduction in ice is thought to be achieved by either the progressive transformation from dislocation walls into new high-angle grain boundaries, called subgrain rotation or polygonisation, or bulging nucleation that is assisted by subgrain rotation. Both our time-resolved numerical modelling and NEEM ice core samples show that grain dissection is a common mechanism during ice deformation and can provide an efficient process to reduce grain sizes and counter-act dynamic grain-growth in addition to polygonisation or bulging nucleation. Thus, our results show that solely strain-induced boundary migration, in absence of subgrain rotation, can reduce grain sizes in polar ice, in particular if strain energy gradients are high. We describe the microstructural characteristics that can be used to identify grain dissection in natural microstructures.

【 授权许可】

CC BY