Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 2: The role of grain size and premelting on ice deformation at high homologous temperature
<p>The ice microstructure in the lower part of the North Greenland Eemian Ice Drilling (NEEM) ice core consists of relatively fine-grained ice with a single maximum crystallographic preferred orientation (CPO) alternated by much coarser-grained ice with a partial (great circle) girdle or multi...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-07-01
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| Series: | The Cryosphere |
| Online Access: | https://tc.copernicus.org/articles/14/2449/2020/tc-14-2449-2020.pdf |
| Summary: | <p>The ice microstructure in the lower part of the North
Greenland Eemian Ice Drilling (NEEM) ice core consists of relatively fine-grained ice with a single maximum crystallographic preferred orientation
(CPO) alternated by much coarser-grained ice with a partial (great circle)
girdle or multi-maxima CPO. In this study, the grain-size-sensitive (GSS)
composite flow law of Goldsby and Kohlstedt (2001) was used to study the
effects of grain size and premelting (liquid-like layer along the grain
boundaries) on strain rate in the lower part of the NEEM ice core. The
results show that the strain rates predicted in the fine-grained layers are
about an order of magnitude higher than in the much coarser-grained layers.
The dominant deformation mechanisms, based on the flow relation of Goldsby
and Kohlstedt (2001), between the layers is also different, with basal slip
rate limited by grain boundary sliding (GBS-limited creep) being the
dominant deformation mechanism in the finer-grained layers, while
GBS-limited creep and dislocation creep (basal slip rate limited by
non-basal slip) contribute both roughly equally to bulk strain in the coarse-grained layers. Due to the large difference in microstructure between finer-grained ice and the coarse-grained ice at premelting temperatures
(<span class="inline-formula"><i>T</i>>262</span> K), it is expected that the fine-grained layers deform at
high strain rates, while the coarse-grained layers are relatively stagnant.
The difference in microstructure, and consequently in viscosity, between
impurity-rich and low-impurity ice can have important consequences for ice
dynamics close to the bedrock.</p> |
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| ISSN: | 1994-0416 1994-0424 |