Ice crystal <i>c</i>-axis orientation and mean grain size measurements from the Dome Summit South ice core, Law Dome, East Antarctica

Abstract

Abstract. We present measurements of crystal c-axis orientations and mean grain area from the Dome Summit South (DSS) ice core drilled on Law Dome, East Antarctica. All measurements were made on location at the borehole site during drilling operations. The data are from 185 individual thin sections obtained between a depth of 117 m below the surface and the bottom of the DSS core at a depth of 1196 m. The median number of c-axis orientations recorded in each thin section was 100, with values ranging from 5 through to 111 orientations. The data from all 185 thin sections are provided in a single comma-separated value (csv) formatted file which contains the c-axis orientations in polar coordinates, depth information for each core section from which the data were obtained, the mean grain area calculated for each thin section and other data related to the drilling site. The data set is also available as a MATLAB™ structure array. Additionally, the c-axis orientation data from each of the 185 thin sections are summarized graphically in figures containing a Schmidt diagram, histogram of c-axis colatitudes and rose plot of c-axis azimuths. All these data are referenced by doi:10.4225/15/5669050CC1B3B and are available free of charge at https://data.antarctica.gov.au.

Crystallographic preferred orientations of ice deformed in direct-shear experiments at low temperatures

“…Many natural CPOs characterized by a single c-axis cluster occur, and some of these are attributed to shear deformation. It is difficult for us to make any comparison between CPOs in natural samples and experimental samples here, as many of the natural samples are not from areas with large-scale shear context (e.g., Treverrow et al, 2016). It is possible that these data represent CPOs in ice sheared to high shear strains.…”

“…Ice CPOs with a vertical c-axis cluster are common in nature (e.g., Gow and Williamson, 1976;Herron and Langway, 1982;Herron et al, 1985;Faria et al, 2014;Treverrow et al, 2016). Such CPOs could relate to vertical sample flattening or to shear with a horizontal shear plane.…”

“…Polycrystalline ice 1 h deformed in the laboratory (e.g., Kamb, 1972;Li et al, 2000;Wilson et al, 2014;Qi et al, 2017) and in nature (e.g., Gow and Williamson, 1976;Hudleston, 1977;Thorsteinsson et al, 1999;Treverrow et al, 2016;Weikusat et al, 2017) develops strong crystallographic preferred orientations (CPOs, often called crystal orientation fabric, COF, in the glaciological literature), usually presented as the preferred orientation of ice [0001] axes, i.e., c axes. As single crystals of ice are most easily deformed by glide on the (0001) plane, i.e., the basal plane (Nakaya, 1958;Wakahama, 1967;Duval et al, 1983), the manner in which the c axes are aligned affects the flow strength for the given applied deformation kinematics, for example, simple shear versus uniaxial compression (e.g., Shoji and Langway, 1988;Azuma, 1995;Li et al, 1996;Duval et al, 2010;Budd et al, 2013).…”

reply to comments of Referee 1

“…It is difficult for us to make any comparison between CPOs in natural samples and experimental samples here, as many of the natural samples are not from areas with large-scale shear context (e.g., Treverrow et al, 2016). It is possible that these data represent CPOs in ice sheared to high shear strains.…”

“…Polycrystalline ice 1 h deformed in the laboratory (e.g., Kamb, 1972;Li et al, 2000;Wilson et al, 2014;Qi et al, 2017) and in nature (e.g., Gow and Williamson, 1976;Hudleston, 1977;Thorsteinsson et al, 1999;Treverrow et al, 2016;Weikusat et al, 2017) develops strong crystallographic preferred orientations (CPOs, often called crystal orientation fabric, COF, in the glaciological literature), usually presented as the preferred orientation of ice [0001] axes, i.e., c axes. As single crystals of ice are most easily deformed by glide on the (0001) plane, i.e., the basal plane (Nakaya, 1958;Wakahama, 1967;Duval et al, 1983), the manner in which the c axes are aligned affects the flow strength for the given applied deformation kinematics, for example, simple shear versus uniaxial compression (e.g., Shoji and Langway, 1988;Azuma, 1995;Li et al, 1996;Duval et al, 2010;Budd et al, 2013).…”