In a study that turns many age-old notions about the formation of polar ice sheets upside down, it has been found that the vast Antarctic ice sheets covering 98 per cent of the continent are not always formed by falling snow, but could have, in places, been the result of refreezing water from below.

The refrozen bottoms up component could in fact account for as much as half of the thickness of the sheet in many places.

Earlier studies had indicated that the overlying layers of ice insulate the base, hemming in heat created there by friction or radiating naturally from the warm planet, causing deeply buried ice to melt. Even if temperatures are below normal freezing point, at great depths the water remains liquid due to the pressure exerted on it.

It has now been established by the study that as this liquid melt-water gets squeezed up the valley walls of the sub-glacial Gamburtsev Mountains or collects in mountain ridges, lower temperatures coupled with decreasing pressure causes it to refreeze and attach itself to the sheet above, adding to the thickness of the overlying sheaf. Almost 24 percent of the ice in an area around Dome A, a 13,800 feet high plateau that forms the top of East Antarctica, is said to have been formed thus.

 This is like someone injected a layer of frosting at the bottom--a really thick layer, said Robin Bell, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory and a co-author of the paper.

The research was conducted as part of a six-nation project studying the invisible Gamburtsev Mountains and the findings have been published in this week's early online edition of the leading journal Science. They are expected to help scientists unravel further facts about the flows of Antarctic and Greenland ice sheets, and aid them in evolving responses to global warming.

Dr. Alexandra Isern, program director for Antarctic earth sciences in the National Science Foundation's Office of Polar Programs confirms this saying, This understanding is critical for the development of climate models that can accurately describe how our planet will react to increased global temperatures.