In situ field measurements of the temporal evolution of low-frequency sea-ice dielectric properties in relation to temperature, salinity, and microstructure

Abstract

Abstract. The seasonal evolution of sea-ice microstructure controls key ice properties, including those governing oceanatmosphere heat and gas exchange, remote-sensing signatures, and the role of the ice cover as a habitat. Nondestructive 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.

Low‐Frequency Induced Polarization of Porous Media Undergoing Freezing: Preliminary Observations and Modeling

“…In this model, we do not account for another polarization mechanism associated with the polarization of the ice itself. We will show later that the polarization of ice may actually happen but at higher frequencies (above 10–100 Hz, for more details about the polarization or dielectric characteristics of ice; Buchanan et al, ; Ingham et al, ; O'Sadnick et al, ).…”

Seasonal evolution of granular and columnar sea ice pore microstructure and pore network connectivity

“…At each step, an X-ray projection was captured on the instrument's 768 × 576 pixel 8-bit camera with a pixel size of 41.5 × 41.5 μm. The X-ray source was set to a voltage of 40 keV and a current of 1 mA with an exposure time of about 540 ms (O'Sadnick and others, 2016). We used the NRecon software (Bruker microCT, Kontich, Belgium) to reconstruct the 3D CT volume.…”

“…Despite the substantial contrasts in microstructure – described as tortuous (Weissenberger and others, 1992; Lieblappen and others, 2018) relative to columnar ice, quantitative data are lacking. The few existing measurements of permeability and resistivity (Freitag, 1999; Freitag and Eicken, 2003; Kawamura and others, 2006; O'Sadnick and others, 2016) are not sufficient to inform the development of fluid flow through granular ice. Hence, the presence of granular ice is often either not considered (Golden and others, 2007; Griewank and Notz, 2013) or aggregated with columnar ice in representations of ice stratigraphy (Buffo and others, 2018).…”