Magnetic resonance imaging of sea-ice pore fluids: methods and thermal evolution of pore microstructure

Citation
H. Eicken et al., Magnetic resonance imaging of sea-ice pore fluids: methods and thermal evolution of pore microstructure, COLD REG SC, 31(3), 2000, pp. 207-225
Citations number
42
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Civil Engineering
Journal title
COLD REGIONS SCIENCE AND TECHNOLOGY
ISSN journal
0165-232X → ACNP
Volume
31
Issue
3
Year of publication
2000
Pages
207 - 225
Database
ISI
SICI code
0165-232X(200012)31:3<207:MRIOSP>2.0.ZU;2-#
Abstract
Microstructure and thermal evolution of sea-ice brine inclusions were inves tigated with magnetic resonance imaging (MRT) techniques. Ice samples were kept at temperatures between -2 degreesC and -25 degreesC during H-1 imagin g in a 4.7-T magnet at 200 MHz. Measurements were completed in a 20-cm diam eter cylindrical probe and actively shielded gradient coils (max. 50 mT m(- 1), pixel dimensions > 0.2 mm, slice thicknesses > 1 mm), and for higher re solution in a mini-imaging unit with a 9-cm diameter probe with gradient co ils of 200 mT m(-1) (pixel dimensions < 0.1 mm, slice thickness < 0.4 mm). Absorption of radio-frequency (RF) signals in the dielectrically lossy brin e resulted in degraded signals and was alleviated by use of a contrast agen t (decane). MRI data and sea-ice thin section images agree very well (< 5% deviation for pore microstructural parameters). Analysis of ice grown under different current speeds indicates that pores are smaller and pore number densities larger at higher current speeds. The thermal evolution of fluid i nclusions was studied on cold first-year ice samples, maintained at close t o in-situ temperatures prior to experiments. Warming from -21<degrees>C to -10 degreesC to -6 degreesC is associated with a distinct increase in pore size (from 1.5 to 1.7 to 2.6 mm for the upper 10-percentile in the vertical ) and elongation (4.0 to 4.2 to 6.2 for ratio of major to minor pore axes i n the vertical) and a decrease in number densities (0.75 to 0.62 to 0.58 mm (-3) in the vertical). Aspect ratios increased from 4:2:1 to 6:2:1 (upper I O-percentile), indicating expansion and merging of pores in the vertical, p ossibly promoted by microscopic residual brine inclusions. (C) 2000 Elsevie r Science B.V. All rights reserved.