DOI: 10.5194/tc-8-319-2014
Scopus记录号: 2-s2.0-84895792322
论文题名: Gas diffusivity and permeability through the firn column at Summit, Greenland: Measurements and comparison to microstructural properties
作者: Adolph A ; C ; , Albert M ; R
刊名: Cryosphere
ISSN: 19940416
出版年: 2014
卷: 8, 期: 1 起始页码: 319
结束页码: 328
语种: 英语
英文关键词: diffusion
; error analysis
; gas transport
; glacial environment
; ice sheet
; measurement method
; microstructure
; numerical model
; permeability
; porosity
; three-dimensional modeling
; Arctic
; Greenland
; Greenland Ice Sheet
英文摘要: The physical structure of polar firn plays a key role in the mechanisms by which glaciers and ice sheets preserve a natural archive of past atmospheric composition. This study presents the first measurements of gas diffusivity and permeability along with microstructural information measured from the near-surface firn through the firn column to pore close-off. Both fine-and coarse-grained firn from Summit, Greenland are included in this study to investigate the variability in firn caused by seasonal and storm-event layering. Our measurements reveal that the porosity of firn (derived from density) is insufficient to describe the full profiles of diffusivity and permeability, particularly at porosity values above 0.5. Thus, even a model that could perfectly predict the density profile would be insufficient for application to issues involving gas transport. The measured diffusivity profile presented here is compared to two diffusivity profiles modeled from firn air measurements from Summit. Because of differences in scale and in firn processes between the true field situation, firn modeling, and laboratory measurements, the results follow a similar overall pattern but do not align; our results constitute a lower bound on diffusive transport. In comparing our measurements of both diffusivity and permeability to previous parameterizations from numerical 3-D lattice-Boltzmann modeling, it is evident that the previous relationships to porosity are likely site-specific. We present parameterizations relating diffusivity and permeability to porosity as a possible tool, though use of direct measurements would be far more accurate when feasible. The relationships between gas transport properties and microstructural properties are characterized and compared to existing relationships for general porous media, specifically the Katz-Thompson (KT), Kozeny-Carman (KC), and Archie's law approximations. While those approximations can capture the general trend of gas transport relationships, they result in high errors for individual samples and fail to fully describe firn variability, particularly the differences between coarse-and fine-grained firn. We present a direct power law relationship between permeability and gas diffusivity based on our co-located measurements; further research will indicate if this type of relationship is site-specific. This set of measurements and relationships contributes a unique starting point for future investigations in developing more physically based models of firn gas transport. © 2014 Authot (s). Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/74885
Appears in Collections: 影响、适应和脆弱性 气候变化与战略
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作者单位: Thayer School of Engineering, Dartmouth College, Hanover, NH, United States
Recommended Citation:
Adolph A,C,, Albert M,et al. Gas diffusivity and permeability through the firn column at Summit, Greenland: Measurements and comparison to microstructural properties[J]. Cryosphere,2014-01-01,8(1)