Abstract
Abstract. The seasonal evolution of sea-ice microstructure controls key ice properties, including those governing ocean–atmosphere heat and gas exchange, remote-sensing signatures, and the role of the ice cover as a habitat. Non-destructive in situ monitoring of sea-ice microstructure is of value for sea-ice research and operations but remains elusive to date. We examine the potential for the electric properties of sea ice, which is highly sensitive to the brine distribution within the ice, to serve as a proxy for microstructure and, hence, other ice transport properties. Throughout spring of 2013 and 2014, we measured complex dielectric permittivity in the range of 10 to 95 kHz in landfast ice off the coast of Barrow (Utqiaġvik), Alaska. Temperature and salinity measurements and ice samples provide data to characterize ice microstructure in relation to these permittivity measurements. The results reveal a significant correlation between complex dielectric permittivity, brine volume fraction, and microstructural characteristics including pore volume and connectivity, derived from X-ray microtomography of core samples. The influence of temperature and salinity variations as well as the relationships between ice properties, microstructural characteristics, and dielectric behavior emerge from multivariate analysis of the combined data set. Our findings suggest some promise for low-frequency permittivity measurements to track seasonal evolution of a combination of mean pore volume, fractional connectivity, and pore surface area-to-volume ratio, which in turn may serve as proxies for key sea-ice transport properties.
Highlights
Sea ice covers a significant fraction of the polar oceans for much of the year
The dispersal of pollutants released under the sea ice is largely controlled by its microstructure, with brine volume fraction and pore connectivity playing a key role in the upward migration and potential surfacing of pollutants such as oil (Karlsson et al, 2011)
Our results show quantitatively that at frequencies below about 10–100 Hz the complex dielectric permittivity of sea ice is largely controlled by the evolution of microstructural characteristics
Summary
Sea ice covers a significant fraction of the polar oceans for much of the year. Ice extent ranges between 3.4 and 15 million km in the Arctic and 2.3 and 20 million km in the Antarctic (Fetterer et al, 2016). In contrast to freshwater ice, the microstructure of sea ice is characterized by brine pores and channels which evolve in size, shape, and spatial arrangement from initial ice formation through melt. These features govern the thermal and mechanical properties of the ice and resultantly impact its behavior on the macroscale (Petrich and Eicken, 2016). Research into the electric properties of sea ice and their link to microstructure was first conducted in the 1970s (Addison, 1969, 1970; Vant et al, 1978; Milton, 1981). With the exception of work by Addison (1969, 1970), the relationship between low-frequency measurements and microstructure remains largely unexplored
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