By Robin E. Bell
When standing on the surface of the East Antarctic ice sheet where the average temperature is -50°C, it is difficult to imagine water moves through a subglacial hydrologic network 3000 meters beneath the camp. While scientists have long thought that there should be water beneath thick ice sheets it has only been over the last 15 years that we have learned that water can collect in lake the size of Lake Ontario, can move between lakes on the order of months and may modulate the speed of ice flowing in the large ice streams and outlet glaciers. During the International Polar Year a seven nation aerogeophysical team surveyed a region the size of California in the high interior of East Antarctica. The radar data reveals a previously unrecognized process of freeze-on that results in significant mass redistribution at the bottom of the ice. While surface accumulation of snow is considered the primary mechanism for ice sheet growth, beneath Dome A 24% of the base by area is frozen-on ice. In some places up to half the ice thickness has been added from below. These ice packages result from conductive cooling of water ponded along ridges of the Gamburtsev Subglacial Mountains and super-cooling of water forced up steep valley walls. Persistent freeze-on thickens the ice column, alters the basal ice temperature and fabric and upwarps the overlying ice sheet, including the oldest atmospheric climate archive, and drives flow behavior not captured in present models.