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| DOI | 10.5194/tc-8-91-2014 |
| Impact of physical properties and accumulation rate on pore close-off in layered firn | |
| Gregory S.A.; Albert M.R.; Baker I. | |
| 发表日期 | 2014 |
| ISSN | 19940416 |
| 卷号 | 8期号:1 |
| 英文摘要 | Investigations into the physical characteristics of deep firn near the lock-in zone through pore close-off are needed to improve understanding of ice core records of past atmospheric composition. Specifically, the permeability and microstructure profiles of the firn through the diffusive column influence the entrapment of air into bubbles and thus the ice age-gas age difference. The purpose of this study is to examine the nature of pore closure processes at two polar sites with very different local temperatures and accumulation rates. Density, permeability, and microstructure measurements were made on firn cores from the West Antarctic Ice Sheet (WAIS) Divide, a site that has moderate accumulation rates with a seasonal climate archive, and Megadunes in East Antarctica, a site that is a natural laboratory for accumulation rate effects in the cold low-accumulation desert. We found that the open pore structure plays a more important role than density in predicting gas transport properties, throughout the porous firn matrix. For firn below 50 m depth at both WAIS Divide and Megadunes, finer-grained layers experience close-off shallower in the firn column than do coarser-grained layers, regardless of which grain size layer is the denser layer at depth. Pore close-off occurs at a critical open porosity that is accumulation rate dependent. Defining pore close-off at a critical open porosity for a given accumulation rate as opposed to a critical total porosity accounts for the pore space available for gas transport. Below the critical open porosity, the firn becomes impermeable despite having small amounts of interconnected pore space. The low-accumulation sites, with generally coarse grains, close off at lower open porosities (∼<10%) than the open porosity (∼>10%) of high-accumulation sites that have generally finer grains. The microstructure and permeability even near the bottom of the firn column are relic indicators of the nature of accumulation when that firn was at the surface. The physical structure and layering are the primary controlling factors on pore close-off. In contrast to current assumptions for polar firn, the depth and length of the lock-in zone is primarily dependent upon accumulation rate and microstructural variability due to differences in grain size and pore structure, rather than the density variability of the layers. © 2014 Author(s). |
| 学科领域 | accumulation rate; bubble; cryosphere; firn; gas transport; grain size; microstructure; permafrost; physical property; porosity; Antarctica; East Antarctica |
| 语种 | 英语 |
| scopus关键词 | accumulation rate; bubble; cryosphere; firn; gas transport; grain size; microstructure; permafrost; physical property; porosity; Antarctica; East Antarctica |
| 来源期刊 | Cryosphere
 |
| 文献类型 | 期刊论文 |
| 条目标识符 | http://gcip.llas.ac.cn/handle/2XKMVOVA/120167 |
| 作者单位 | Thayer School of Engineering, Dartmouth College, Hanover, NH 03766, United States |
| 推荐引用方式 GB/T 7714 | Gregory S.A.,Albert M.R.,Baker I.. Impact of physical properties and accumulation rate on pore close-off in layered firn[J],2014,8(1). |
| APA | Gregory S.A.,Albert M.R.,&Baker I..(2014).Impact of physical properties and accumulation rate on pore close-off in layered firn.Cryosphere,8(1). |
| MLA | Gregory S.A.,et al."Impact of physical properties and accumulation rate on pore close-off in layered firn".Cryosphere 8.1(2014). |
| 条目包含的文件 | 条目无相关文件。 | |||||
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