Permeability of young sea ice from microtomographic images

• Main Author: Büttner, Juliane
• Format: Master Thesis
• Language: English
• Published: The University of Bergen 2011
• Subjects: Microstructure; Porosity; Sea ice; Permability; VDP::Mathematics and natural science: 400::Geosciences: 450::Oceanography: 452; Borge; Svalbard; Kongsfjord*; Kongsfjorden
• Online Access: https://hdl.handle.net/1956/5633

The author has since publication changed name to: Juliane Borge. The permeability of sea ice controls the transport of substances through the ice and thereby its surface properties as well as the exchange of heat, salt and gas between ice, ocean and atmosphere. More observations and understanding are necessary to properly implement the impact of permeability on sea ice melt and growth in models. This study employs and evaluates a microscopical approach to determine permeability. We combine structure-preserving field sampling with non-destructive synchrotron-based microtomography (SXRT) and lattice Boltzmann modelling (LBM) of fluid flow. Samples of young sea ice from Kongsfjorden, Svalbard, were centrifuged at their respective in situ temperatures before SXRT was performed at temperatures below -40°C, resulting in 3-dimensional images 1.2x1.2x1.7cm3 in size with a resolution of 11.84 μm. From these images microstructural characteristics of sea ice were derived and fluid flow through the samples was modelled with LBM at 22 and 35 μm resolution to obtain directional values of permeability for all three directions. Our method is limited to small sample sizes due to constraints with respect to computer memory and imaging. Therefore it might not be appropriate for all types of ice. With increasing computer memory and parallelization the applicability of this method will increase. Its major advantage over conventional permeability measurements is that it produces a 3-dimensional representation of the pore space which allows for the derivation of microstructural quantities and for modelling processes such as fluid flow or radiative transfer. Quantities derived from the microstructure were different porosities, a critical length scale, minor and major ellipse axis lengths, pore volume to surface ratio, two-point correlation length, pore radius and area distributions as well as measures of hydraulic and electrical tortuosity. Their intercorrelations and porosity dependence varied with ice type. Our data suggested a ...