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Title: Bubbles and bubble pressures in Antarctic glacier ice
Authors: National Science Foundation (U.S.). Office of Antarctic Programs
Gow, A. J. (Anthony Jack)
Keywords: Ice
Ice density
Ice cap
Ice sheet
Ice cores
Glacier ice
Drill hole
Publisher: Cold Regions Research and Engineering Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Research report (Cold Regions Research and Engineering Laboratory (U.S.)) ; 249.
Description: Research Report
Abstract: Application of the gas law to fourth-place density measurements of ice samples from two deep drill holes at Byrd Station and Little America V, Antarctica, shows that virtually all density increase beyond the pore close-off density (0.830 g/cm^3) can be attributed to compression of the entrapped bubbles of air. Data from Byrd Station also indicate that the lag between overburden pressure and bubble pressure, initially 4-5 kg/cm^2 at pore close-off, diminishes to less than 1.0 kg/cm^2 at about 200-m depth. By substituting the overburden pressure for the bubble pressure in the pressure-density relationship based on the gas law, ice densities below 200 m can be calculated more accurately than they can be measured per se on cores because of the relaxation that occurs in samples recovered from high confining pressures. This relaxation, resulting in a progressive increase in the bulk volume of the ice with time, is generally attributed to decompression of the entrapped air bubbles following removal of the ice from high confining pressures. However, calculations of the stress in ice due to bubble pressure, together with measurements of bubble sizes in cores from various depths at Byrd Station, both tend to indicate that there has'been negligible decompression of the inclosed bubbles. It is suggested that most of this relaxation may be due to the formation of microcracks in the ice. Anomalous bubble pressure-density relations at Little America V tend to confirm abundant stratigraphic evidence of the existence of considerable deformation in the upper part of the Ross Ice Shelf. Studies of crystal-bubble relations at Byrd Station revealed that the concentration of bubbles in ice remains remarkably constant at approximately 220 bubbles per cm^3. Bubbles and crystals were found to be present in approximately equal numbers at pore close-off at 64-m depth, at which level the average bubble diameter was 0.95 mm, decreasing to 0.49 mm at 116 m and to 0.33 mm at 279 m. Despite a tenfold increase in the size of crystals between 64 and 279 m, the bubbles showed no tendency to migrate to grain boundaries during recrystallization of the ice. The observation that most of the bubbles had assumed substantially spherical shapes by 120-m depth points to essentially hydrostatic conditions in the upper layers of the ice sheet at Byrd Station.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Research Report

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