Geoelectric Array Measurements of Sea Ice Porosity for Scientific and Operational In-situ Ice Property Assessments

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This Small Grant for Exploratory Research is to develop and field-test methods for taking automated in situ dc resistivity measurements in sea ice. This will allow researchers to track the evolution of sea ice profile properties and to fill a current gap in the real-time monitoring of local ice conditions needed to assess ice strength and trafficability. Experimental work involves cross-borehole tomography measurements not previously performed in sea ice, and applying a microstructurally-realistic improved analysis of Wenner array soundings. Both methods exploit the large resistivity contrast between saline brine and pure ice, which makes the bulk resistivity of sea ice very sensitive to the connectivity of the interior brine volume. The proposed site for this work is landfast first-year ice near Barrow, Alaska, offering the benefits of accessible and readily-monitored ice and proximity to logistics support. The measurements will be complemented by full ice characterization data collected at a nearby mass balance site installed by our group as part of the nascent Alaska Ocean Observing System. Through collaboration with a solid-earth geophysicist with expertise in geoelectric array measurements, substantial synergistic benefits will also be derived from this project. Resistivity measurements in low temperature winter ice and during spring warming are ideally suited to assess theoretical predictions of the appearance and evolution of a 'percolation threshold' in the brine volume connectivity, and other critical transitions in ice profile properties, such as substantial reductions in ice strength in the high-porosity (10%) regime. The lack of appropriate field data (in particular time series) is significantly limiting progress in the research field, and this work aims to evaluate potential benefits that can be derived from novel geoelectric array measurements, owing to their high sensitivity, nondestructive nature and suitability for easy deployment in existing drifting sensor networks. This project will enhance research infrastructure by (1) developing a method (and corresponding instrumentation) that helps close a significant gap in drifting sensor networks which do not provide information on the state of the ice cover and its transport properties; (2) providing for a means to test and refine the applicability of percolation theory to a number of important sea ice geophysical phenomena; (3) laying the foundation for routine in situ monitoring of the state of the ice cover as applicable for engineering and operational applications (such as those relying on sea ice as a stable platform for transport and logistics); and (4) enhancing collaboration and exchange between the solid-earth geophysics and sea-ice glaciology communities to address common problems of materials at high homologous temperatures. These aspects of the project will be introduced into education by involving graduate students in the research and integrating the collaboration into an interdisciplinary seminar series examining porous media from volcanological and glaciological perspectives.