Sulphuric acid at grain boundaries in Antarctic ice

It has been suggested1,2 that acids in the cold polar ice sheets may exist as aqueous mixtures at grain boundaries. This assumption can correctly predict the d.c. conductivity of polar ice2, but this does not prove the existence of acids or liquid veins at grain boundaries, and this remains controversial3–5. In this study we used a scanning electron microscope (SEM), equipped with a cold stage and an energy-dispersive X-ray microanalysis facility, to determine the location of sulphur in ice from the Antarctic Peninsula. As expected, sulphur was undetectable in the bulk of the ice. However, at the junctions where three grains met (triple-junctions), sulphur was found in concentrations greater than 1 M in areas of < 1 μm2. Calculations show that between 40 and 100% of the sulphuric acid present in this ice was found at the triple-junctions, and would have been liquid at ice-sheet temperatures. This finding, if general, has considerable implications for many of the physical properties of polar ice

Recent atmospheric warming and retreat of ice shelves on the Antarctic Peninsula

IN 1978 Mercer1 discussed the probable effects of climate warming on the Antarctic Ice Sheet, predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the Antarctic Peninsula. Analyses of 50-year meteorological records have since revealed atmospheric warming on the Antarctic Peninsula2,3, and a number of ice shelves have retreated4–8. Here we present time-series of observations of the areal extent of nine ice shelves on the Antarctic Peninsula, showing that five northerly ones have retreated dramatically in the past fifty years, while those further south show no clear trend. Comparison with airtemperature data shows that the pattern and magnitude of ice-shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability, the isotherm associated with this limit having been driven south by the atmospheric warming. Ice shelves therefore appear to be sensitive indicators of climate change