HR: 0830h
AN: C11C-0842    [PDF]
TI: Layered Nature With Different Physical Properties Of Firn
AU: * Okuyama, J
EM: jokuyama@hhp2.lowtem.hokudai.ac.jp
AF: Graduate School of Environmental Earth Science, Hokkaido University, N10 W5, Sapporo, 060-0810 Japan
AU: Fujita, S
EM: sfujita@pmg.nipr.ac.jp
AF: National Institute of Polar Research, 1-9-10 Kaga, Itabashi-ku, Tokyo, 173-8515 Japan
AU: Takeya, S
EM: s.takeya@aist.go.jp
AF: National Institute of Advanced Industrial Science and Technology, 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo, 062-8517 Japan
AU: Koerner, R M
EM: RKoerner@NRCan.gc.ca
AF: Glaciology Section, Terrain Sciences Division, Geological Survey of Canada, 601 Booth Street, Ottawa, K1A 0E8 Canada
AU: Hondoh, T
EM: hnd@hhp2.lowtem.hokudai.ac.jp
AF: Institute of Low Temperature Science, Hokkaido University, N19 W8, Sapporo, 060-0819 Japan
AB: To better understand the formation mechanism of the layered structures in firn, we have introduced new methods to clarify the various physical properties relating to the firn-densification process; that is, the X-ray transmission method for detailed profile of density, the X-ray CT for the anisotropy of crystal shapes, the X-ray diffraction method for the crystallographic orientations of both 0002 and 11-20, and the open resonator method for the dielectric permittivity tensor at microwave frequency. These methods have been applied to the firn in both the Dome Fuji ice core from East Antarctica and the P96 ice core from Penny Ice Cap, Baffin Island, Canada. We have found by these measurements that (1) the crystal shapes elongated vertically near the surface turn into spherical ones with depth, (2) the layers with the preferential c axis orientations (fabrics) in vertical alternate with those in horizontal, (3) these preferential orientations gradually vary towards random ones with depth, but (4) there still exist the layered structures with different fabrics even at the close-off depth, and (5) the dielectric anisotropy, or the difference between the dielectric constants parallel and perpendicular to the core axis, decreases with depth. On the basis of these findings, we propose a grain-rotation mechanism during the firn-densification process, which well explains the finding (3). The finding (4) suggests that ice below the close-off depth is also composed of the layered structures with different fabrics. Since the difference in fabrics between layers increases by plastic deformation of grains below the close-off depth, the layered structures with different fabrics must be developed with depth.
DE: 1827 Glaciology (1863)
DE: 3902 Creep and deformation
DE: 5109 Magnetic and electrical properties
DE: 5112 Microstructure
SC: Cryosphere [C]
MN: 2003 Fall Meeting