Microstructural Investigation of Sea Ice and Imaging of Oil in Sea Ice by X-Ray micro-computed tomography

Abstract

The alarming decline of sea ice extent over the last few decades has made the polar marine region and its resources more accessible to humans. This has resulted in increased shipping and mining activities in this area which in turn raise the probability of extremely hazardous and environmentally damaging oil spills in ice-covered waters. Experimental studies and scientific analyses of sea ice microstructure are essential to describe the morphological, physical and physiomechanical properties of sea ice and hence develop strategies to deal with potentially devastating oil spills in ice-covered waters. To this end, we performed laboratory and field experiments combined with non-destructive X-ray micro-computed tomography investigations of clean sea ice and sea ice hosting oil and diesel. Based on the acquired data sets i) the evolution of sea ice on a pore scale and ii) the effect of oil in the sea ice pore space were studied. Oil-free sea ice cores harvested during a field experiment in spring 2016 allowed us to study a wide variety of properties of young Arctic sea ice. Our investigations show that bulk properties such as salinity and density and structural properties such as the pore size strongly depend on the total brine porosity. The collected data set demonstrated little change in the variation of salinity, density, and pore sizes between samples. Nevertheless, we examined a significant decrease in pore number and an increase in pore connectivity over time. In order to accurately analyse and interpret the distribution of oil and diesel distribution within sea ice imaged from computed tomography scans, different segmentation methods were developed. The segmentation approach methods developed in this study were designed to differentiate the low absorption contrast of oil/ diesel and ice and allowed us to investigate the oil and diesel distribution on a microscopic scale. We investigated the oil and diesel distribution on a selection of samples from four different experiments. We examined dispersed spread oil in the upper part of the ice cores and more channelized oil inclusion in the lower part of sea ice and with an average oil filled pore size of 0.04-0.2 mm.