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Metamorphism of stratified firn at Dome Fuji, Antarctica : A mechanism for local insolation modulation of gas transport conditions during bubble close off

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Title: Metamorphism of stratified firn at Dome Fuji, Antarctica : A mechanism for local insolation modulation of gas transport conditions during bubble close off
Authors: Fujita, Shuji Browse this author
Okuyama, Junichi Browse this author
Hori, Akira Browse this author
Hondoh, Takeo Browse this author
Issue Date: 30-Sep-2009
Publisher: American Geophysical Union
Journal Title: Journal of Geophysical Research : Earth Surface
Volume: 114
Start Page: F03023
Publisher DOI: 10.1029/2008JF001143
Abstract: The evolution of the structure of a 112.59-m-long firn core recovered at Dome Fuji, East Antarctica, was investigated in order to improve understanding of firn densification and bubble formation processes, which are important for interpreting local insolation proxies used for astronomical dating of deep ice cores. Using selected samples, we measured physical properties including (i) the relative dielectric permittivities in both the vertical and horizontal planes, (ii) the bulk density at a resolution of millimeters, (iii) the three-dimensional geometric structure of pore space, and (iv) crystal orientation fabrics. We found that the firn at Dome Fuji contains horizontal strata with thicknesses of several centimeters. Near the surface of the ice sheet, these strata are characterized by contrasting bulk density. Earlier field studies suggest that summer insolation causes densification of surface firn. Down to ~30 m, density maxima exhibited a clear positive correlation with the strength of structural anisotropy and c-axis clustering around the vertical. In contrast, the correlation is negative in deeper firn, confirming previous findings that initially less dense firn became denser than initially dense firn. In addition, numerous examples of textures indicating that deformation preferentially occurred in weaker layers were found. Moreover, the initially dense firn layers were more permeable for air near the bottom of firn. We propose a model linking firn properties with conditions for the gas transport processes near the bottom of firn. The model explains how stronger insolation can lead to bulk ice with a lower O2/N2 ratio and smaller total gas content.
Rights: An edited version of this paper was published by AGU. Copyright 2009 American Geophysical Union.
Type: article (author version)
Appears in Collections:低温科学研究所 (Institute of Low Temperature Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 本堂 武夫

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