Temporal variations in sea ice resistivity: Resolving anisotropic microstructure through cross‐borehole DC resistivity tomography

Abstract

[1] The distribution and connectivity of brine pockets in first year sea ice has a determining influence on the bulk properties of the ice and its interaction with the environment. The structure of the brine network depends upon both temperature and salinity, and a full understanding of the temporal evolution of sea ice physical properties requires measurements that are sensitive to the microstructure and can also be made without disturbing the natural state of the ice. Direct current resistivity techniques are suited to this as the brine fraction is orders of magnitude more conductive than solid ice. However, due to the preferential vertical alignment of brine inclusions, the bulk resistivity of first year sea ice is anisotropic. Although this makes the interpretation of surface resistivity soundings extremely difficult, consideration of the theory of resistivity measurements in an anisotropic medium shows that the anisotropic resistivity structure may be resolved through cross-borehole measurements. Borehole pairs with one current and one potential electrode in each hole allow the determination of the horizontal component of the anisotropic bulk resistivity (r H ). Use of four boreholes allows an estimate of the geometric mean resistivity (r m ) to be derived. Combining these measurements allows calculation of the vertical resistivity (r V ). This is illustrated by measurements made in first year sea ice near Barrow, Alaska in April-June 2008. Over this period significant changes in resistivity are observed which may be shown to be related to both the brine volume fraction and the microstructure of the ice.

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

“…The positive relationship found between ε and brine volume fraction is therefore in agreement with the relationship between ε and temperature. Similarly the strong positive correlation at all frequencies between ε and brine volume fraction is in agreement with the increase in bulk DC conductivity of sea ice which occurs as brine volume fraction increases -previously observed and modeled by Jones et al (2010Jones et al ( , 2012. How temperature and brine volume fraction may separately influence measurements of ε is displayed in Fig.…”

“…The relationship between ε and connectivity is established for laboratory grown and modeled sea ice (D. Jones et al, 2010). The data we present expand on previous findings and reveal a similar relationship in natural sea ice.…”

“…They tie errors in estimates of ice thickness derived from surface resistivity to ice anisotropy and link the error to significant differences in the horizontal vs. vertical resistivity. Building on this finding, Jones et al (2010) applied a cross-borehole technique to track ice anisotropy and the formation and growth of brine channels more closely; their results show a relationship between resistivity, the temperature of the ice, and time of year. The study by Jones et al (2010) supports the ability of electrical measurements to track the connectivity of brine pores as the ice nears the percolation threshold (D. J.…”

Electrical anisotropy in sea ice and a dual-polarization radar system to mitigate the effects of preferential attenuation in imaging sea ice

“…In general, these brine pockets are probably ellipsoidal or cylindrical ( Fig. 1) (Jones et al, 2010;Kovacs and Morey, 1986;Morey et al, 1984). Nevertheless, the volume fraction, size, shape, and connectivity of the brine inclusions vary over several orders of magnitude depending on environmental factors (Arcone et al, 1986a;Buchanan et al, 2011;Jones et al, 2010).…”

“…The concentration of the brine within the inclusions depends largely on the rate of ice growth for early-or mid-season ice. Ice growth rates, in turn, depend on temperature and on the age and thickness of the ice (Arcone et al, 1986b;Jones et al, 2010).…”