Scientists say that part of the world's largest ice shelf, the size of France, is melting 10 times faster than expected due to the warming of the sea around it.
The research suggests that the Ross ice shelf, a floating plate of Antarctic ice, several hundred meters thick, is more vulnerable to global warming than previously thought.
The loss of ice shelves removes a barrier to the glaciers that carry water into the ocean, allowing sea level to rise.
A four-year study by a team at Cambridge University investigated how the northwest portion of the ice interacted with the ocean beneath it.
Craig Stewart, a former Cambridge scientist, said: "The stability of ice shelves is thought to be related to exposure to hot ocean water, but we have found that solar-heated surface water also plays a crucial role in melting of the ice shelves ".
Temperature, salinity, melt rate and ocean currents were measured using instruments passed through a 260m (850ft) hole.
An oceanographic mooring installed under the ice shelf was also used to collect data, and a tailor-made radar system was used to assess the change in ice thickness.
The team found that water from the sun-warmed surface was entering the cavity under the ice shelf, causing melting rates to nearly triple in the summer.
Dr. Stewart added, "Climate change is likely to result in less sea ice and ocean temperatures on the higher surface in the Ross Sea, suggesting that melting rates in this region will increase in the future."
Co-author Poul Christoffersen of the University of Cambridge's Scott Polar Research Institute has pointed out that ice shelves can double or triple the speed with which glaciers flow into the ocean.
"The difference here is the size of Ross's ice shelf, which is 100 times larger than the ice shelves we've already seen disappear.
"The observations we made in front of the ice shelf have direct implications for many large glaciers that flow to the ice shelf, some up to 900 kilometers away."
The findings are published in the latest addition to the journal Nature Geoscience.