A magnetic resonance study of temperature-dependent microstructural evolution and self-diffusion of water in Arctic first-year sea ice

Abstract

The microstructural evolution of brine inclusions in granular and columnar sea ice has been investigated through magnetic resonnance imaging (MRI) for temperatures between -28 and-3°C. Thin-section and salinity measurements were completed on core samples obtained from winter sea ice near Barrow, Alaska, USA. Subsamples of granular (2-5 cm depth in core) and columnar sea ice (20-23 cm depth) were investigated with morphological spin-echo and diffusion-weighted imaging in a Bruker 4.7T MRI system operating at field gradients of 200 mTm-1 at temperatures of approximately -28, -15, -6 and -3°C. Average linear pore dimensions range from 0.2 to 1 mm and increase with bulk liquid volume fraction as temperatures rise from - 15 to -3°C. Granular ice pores are significantly larger than columnar ice pores and exhibit a higher degree of connectivity. No evidence is found of strongly non-linear increases in pore connectivity based on the MRI data. This might be explained by shortcomings in conditions or the absence of a percolation transition. Pore conncetivity increases between -6 and -3°C. Pore-number densities average at 1.4±1.2mm-2. The pore number density distribution as a function of cross-sectional area conforms with power-law and lognormal distributions previously identified, although significant variations ocur as a function of ice type and temperature. At low temperature ( <1 μm at