Abstract
Abstract. We performed numerical simulations on the microdynamics of ice with air inclusions as a second phase. Our aim was to investigate the rheological effects of air inclusions and explain the onset of dynamic recrystallization in the permeable firn. The simulations employ a full-field theory crystal plasticity code coupled to codes simulating dynamic recrystallization processes and predict time-resolved microstructure evolution in terms of lattice orientations, strain distribution, grain sizes and grain-boundary network. Results show heterogeneous deformation throughout the simulations and indicate the importance of strain localization controlled by air inclusions. This strain localization gives rise to locally increased energies that drive dynamic recrystallization and induce heterogeneous microstructures that are coherent with natural firn microstructures from EPICA Dronning Maud Land ice coring site in Antarctica. We conclude that although overall strains and stresses in firn are low, strain localization associated with locally increased strain energies can explain the occurrence of dynamic recrystallization.
Highlights
The ice sheets on Greenland and Antarctica are composed of snow layers, originally containing a large proportion of air, which are transformed into solid ice due to compaction and sintering processes (Herron and Langway, 1980; Colbeck, 1983)
Systematic numerical studies of the effect of a second phase, in this case air, on plastic deformation and concurrent microstructure evolution during DRX are still lacking. In this contribution we investigate the implications of air inclusions on deformation and recrystallization to assess the importance of DRX at shallow levels of ice sheets
We used polyphase numerical models of deformation and recrystallization to investigate the occurrence of dynamic recrystallization in an air–ice composite such as polar ice and firn
Summary
The ice sheets on Greenland and Antarctica are composed of snow layers, originally containing a large proportion of air, which are transformed into solid ice due to compaction and sintering processes (Herron and Langway, 1980; Colbeck, 1983). At the firn–ice transition, the air is sealed off in bubbles as the pores are no longer connected and do not allow exchange with air from other layers or the atmosphere (Schwandner and Stauffer, 1984; Stauffer et al, 1985). For this reason, the ice sheets are considered as valuable archives of the palaeoatmosphere (Luethi et al, 2008; Fischer et al, 2008). For the interpretation of these records it is essential to understand the deformation dynamics of polycrystalline ice and the implications of a second phase in the form of air bubbles. We use the expression “air bubbles” whenever referring to the natural material and air inclusion only for numerical models, where the individual units of air are neither interconnected nor communicating
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