Evidence of dynamic recrystallization in polar firn

Kipfstuhl, Sepp; Faria, Sérgio H.; Azuma, Nobuhiko; Freitag, Johannes; Hamann, Ilka; Kaufmann, Patrik; Miller, Heinrich; Weiler, Karin; Wilhelms, Frank (2009). Evidence of dynamic recrystallization in polar firn. Journal of geophysical research, 114(B5) Washington, D.C.: American Geophysical Union 10.1029/2008JB005583

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Microstructural analyses have been performed on polar firn from the European Project for Ice Coring in Antarctica drilling site in Dronning Maud Land, Antarctica. The results derived from images of the firn structure in microscopic resolution indicate that dynamic recrystallization is active in firn at all depths, and it dominates the evolution of the microstructure when the firn density exceeds a critical value of 730 kg/m3 (overburden snow load ∼0.2 MPa). At the firn-ice transition (density ∼820 kg/m3) the microstructure is characterized by many small grains and bulged or irregularly shaped grain boundaries. More than half of all grains show subgrain boundaries. Thus, strain-induced boundary migration is an essential feature to describe the irregular grain structure. In agreement with previous studies, significant grain growth has been observed with depth for the largest grains in the samples. However, our microscopic analysis reveals that the grain growth with depth in fact vanishes if all grains larger than 65 μm in diameter are taken into account. This result reflects the fact that the growth of the largest grains is counteracted by grain size reduction by shrinking and subdivision of old grains, as well as production of new grains. Consequently, previous conclusions that grain growth in polar firn is essentially analogous to normal grain growth in metallic and ceramic sinters and that the stored strain energy is small in comparison with grain boundary energy can no longer be supported. Additionally, our observations show that the incipience of dynamic recrystallization in polar ice sheets is not as sensitive to temperature as supposed so far. A discussion of the change of the mean grain size due to the measuring technique is imperative.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Climate and Environmental Physics
08 Faculty of Science > Physics Institute

UniBE Contributor:

Kaufmann, Patrik and Weiler, Karin

ISSN:

0148-0227

Publisher:

American Geophysical Union

Language:

English

Submitter:

Factscience Import

Date Deposited:

04 Oct 2013 15:23

Last Modified:

05 Dec 2022 14:26

Publisher DOI:

10.1029/2008JB005583

Web of Science ID:

000266365300001

BORIS DOI:

10.48350/37523

URI:

https://boris.unibe.ch/id/eprint/37523 (FactScience: 208799)

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