In:
The Cryosphere, Copernicus GmbH, Vol. 14, No. 7 ( 2020-07-27), p. 2429-2448
Kurzfassung:
Abstract. The effect of grain size on strain rate of ice in the
upper 2207 m in the North Greenland Eemian Ice Drilling (NEEM) deep ice core
was investigated using a rheological model based on the composite flow law
of Goldsby and Kohlstedt (1997, 2001). The grain size was described by both
a mean grain size and a grain size distribution, which allowed the strain
rate to be calculated using two different model end-members: (i) the
microscale constant stress model where each grain deforms by the same
stress and (ii) the microscale constant strain rate model where each grain
deforms by the same strain rate. The model results predict that grain-size-sensitive flow produces almost all of the deformation in the upper 2207 m of
the NEEM ice core, while dislocation creep hardly contributes to
deformation. The difference in calculated strain rate between the two model
end-members is relatively small. The predicted strain rate in the fine-grained Glacial ice (that is, ice deposited during the last Glacial maximum
at depths of 1419 to 2207 m) varies strongly within this depth range and,
furthermore, is about 4–5 times higher than in the coarser-grained Holocene
ice (0–1419 m). Two peaks in strain rate are predicted at about 1980 and
2100 m depth. The prediction that grain-size-sensitive creep is the
fastest process is inconsistent with the microstructures in the Holocene age
ice, indicating that the rate of dislocation creep is underestimated in the
model. The occurrence of recrystallization processes in the polar ice that
did not occur in the experiments may account for this discrepancy. The
prediction of the composite flow law model is consistent with
microstructures in the Glacial ice, suggesting that fine-grained layers in
the Glacial ice may act as internal preferential sliding zones in the
Greenland ice sheet.
Materialart:
Online-Ressource
ISSN:
1994-0424
DOI:
10.5194/tc-14-2429-2020
Sprache:
Englisch
Verlag:
Copernicus GmbH
Publikationsdatum:
2020
ZDB Id:
2393169-3
