We have drilled 13 boreholes within and around a through-cutting rift on the (unofficially named) Roi Baudouin Ice Shelf, East Antarctica. Logging by optical televiewer (OPTV) combined with core inspection has resulted in the identification and characterization of several material facies. Outside the rift, OPTV-imaged annual layering indicates ~150 years of accumulation over the 66 m length of one of the boreholes. Luminosity analysis of this image also reveals the presence of numerous dark melt layers as well as a systematic decrease in background luminosity, interpreted in terms of a progressive increase in light transmission during firnification. We identify four material facies within the rift: snow, granular ice, marine ice and unconsolidated platelets. We interpret the granular ice facies as snow that has been saturated by percolating sea water, and the underlying marine ice as compacted buoyant platelets that have adhered to the rift base. Core sections reveal the presence of tubular channels within the marine ice, indicating that it is macroporous and permeable to sea water. The lower boundary of this facies merges into a mushy layer of unconsolidated platelets that were successfully imaged by OPTV, revealing irregular sub-horizontal layering similar to that reported previously on the basis of (directional) borehole video.

During three summer field seasons (2003, 2005 and 2006) we carried out radio-echo sounding measurements with a 5MHz (central frequency) ice-penetrating radar on McCall Glacier, Arctic Alaska, USA, along the central flowline and 17 cross-profiles. Two-way travel time was, after migration, converted to ice thickness, which, in combination with a recent digital elevation model of the surface of the glaciated area, resulted in a detailed map of the bed topography. This reveals a complex basal topography in the confluence area of the different glacial cirques. The pattern of subglacial water flow following the hydraulic potential gradient was calculated for the whole glacier area and shows a confluence of subglacial water downstream from the confluence of the glacier cirques. From the ice-thickness map the total ice volume was estimated as slightly less than 0.5 km3. Bed reflection power (BRP) was determined for the glacier after correction for ice-thickness dependence. Results reveal a clear relationship between the BRP pattern and basal sliding anomalies along the central flowline.

To improve our understanding of the deformation properties of cold-based polar glaciers, we examine here some of the factors leading to the localization of strain within the amber ice facies. We present a crystallographic case study of amber ice (a fine-grained bubbly ice containing a relatively high impurity content) sampled at the base of two Antarctic glaciers. The crystal fabrics and textures of amber ice were computed by application of a recently developed automated method. To date, it was tedious and awkward to determine amber ice facies accurately because of the sub-millimetric crystal size and relatively high debris content of this facies. The authomatic analytical method applied in this study allows not only for improving analytical accuracy in this task but also for considerably reducing the time of analysis. Our investigations reveal highly homogeneous crystallographic properties for the studied amber ice. The ice crystals are mainly polygonal, equant and sub-millimetric, and show a strong lattice-preferred orientation. These properties, beside the relatively high impurity content, are likely to exert a major control on strain enhancement in amber ice when this facies is present at the base of cold glaciers.

Three debris-bearing ice facies were recognized at the base of Suess Glacier, a cold-based glacier damming a lake in Taylor Valley, South Victoria Land, Antarctica. These facies are termed “amber ice”,“solid facies” and “basal stratified facies”. This paper uses stable-isotope composition (δD and δ18O), gas content and gas composition (CO2, O2 and N2) to develop an understanding of the processes responsible for the formation of these facies. The basal ice is characterized by a striking difference in ice properties between the innermost end of a 25 m long tunnel dug 200 m upstream from the glacier front and the front itself. At the glacier front, co-isotopic data plot along a well-defined freezing slope (S = 5.6), whereas, inside the tunnel, the isotopic data offset from the freezing slope and from the local meteoric water-line (which has a slope of 8.2). CO2 concentrations rise from a minimum of about 1000 ppmv in the tunnel to about 220000ppmv at the front. Taken together, these characteristics strongly suggest an increasing contribution of liquid water in the formation of basal ice towards the glacier terminus. We therefore conclude that visually similar basal ice facies can have different origins.

This paper reports detailed textural and gas measurements conducted in cold basal ice (–17°C from the margin of Taylor Glacier, an outlet glacier of the East Antarctic ice sheet. The analyzed samples were retrieved from a basal ice sequence excavated at the end of a subglacial tunnel dug near the glacier snout. The basal sequence exhibits two contrasting ice facies, defined as the englacial and stratified facies. On the one hand, analysis of ice crystal textures from the basal ice sequence provides evidence for localized ductile deformation, especially within the stratified facies where significant dynamic recrystallization was detected. On the other hand, high-resolution gas analyses reveal that strong changes in gas composition occurred at the structural interfaces of the stratified facies. These gas composition changes are typical of melting–refreezing processes but are not associated with any significant loss of gas volume. Given the specific subglacial thermal conditions at the margin of Taylor Glacier, we interpret this phenomenon as resulting from microscopic phase changes involving selective gas redistribution through the pre-melt phase. It is argued that such processes may play an important role in the post-genetic geochemical evolution of cold debris-laden ice and may be enhanced through intense strain conditions.

This paper examines the basal ice sequence of Rhone Glacier, a cold-based glacier in the McMurdo Dry Valleys, Antarctica, using isotopic and solute chemistry data. Three different ice facies are identified: englacial, amber and stratified. The englacial facies is clean, bubbly ice of meteoric origin and is underlain by an amber facies. Amber ice is a characteristic of cold alpine glaciers in the McMurdo Dry Valleys and is distinctive for its high solute concentrations and much higher strain rates compared with the overlying englacial ice and the underlying stratified ice. Analysis of the stratified facies reveals an isotopic signature indicative of melt then refreeze processes and it is most likely associated with apron entrainment at the margin. By contrast, the amber facies has a co-isotopic slope of 8 and plots on a meteoric waterline. The inclusion of impurities in the amber ice reveals prolonged contact with the bed, and its depleted isotopic signature is consistent with ice formed during a cooler period. Comparison of the basal sequence of Rhone Glacier with other cold-based glaciers in the McMurdo Dry Valleys reveals strong similarities between valley-side glaciers (e.g. Meserve and Rhone Glaciers), whereas valley-floor glacier basal sequences (e.g. Suess Glacier) are characterized by structurally complex amalgamations of ice and debris.

Digital optical televiewing, recently developed to log and map terrestrial boreholes, provides a complete orientated image of borehole walls at a resolution of 1 mm along hole and typically <1 mm around hole. Here we provide an overview of optical televiewer (OPTV) technology and operation, and outline the potential contributions of the technique to ice-mass research with reference to an OPTV log of a borehole ∼21 m deep drilled in the lower accumulation area of Glacier de Tsanfleuron, Switzerland. The OPTV image of this borehole successfully reveals a variety of visibly contrasting ice types. These ice types have been characterized and their orientation mapped and, on the basis of this information, interpreted as: (1) primary foliation; (2) summer/autumn erosion surfaces; and (3) incipient foliation. Importantly, unrolled OPTV images can be inverted to recreate a virtual image of the borehole core, potentially, for the first time, allowing ice cores to be orientated.

Marine ice accretes at the base of ice shelves, often infilling open structural weaknesses and increasing ice-shelf stability. However, the timing and location of marine ice formation remain poorly understood. This study determines marine ice source water composition and origin by examining marine ice crystal morphology, water isotope and solute chemistry in ice samples collected from the southern McMurdo Ice Shelf (SMIS), Antarctica. The measured co-isotopic record together with the output of a freezing model for frazil crystals indicate a spatio-temporally varying water source of sea water and relatively fresher water, such as melted meteoric or marine ice. This is in agreement with the occurrence of primarily banded and granular ice crystal facies typical for frazil ice crystals that nucleate in a supercooled mixture of water masses. We propose that marine ice exposed at the surface of SMIS, which experiences summer melt, is routed to the ice-shelf base via the tide crack. Here frazil crystals nucleate in a double diffusion mechanism of heat and salt between two water masses at their salinity-dependent freezing point. Recycling of previously formed marine ice facilitates ice-shelf self-sustenance in a warming climate.