Scientists are concerned that greater collapses will now occur in the Antarctic Peninsula.
Satellite images from the European Space Agency show that a 25-mile-long strip of ice believed to pin the Wilkins Ice Shelf in place had splintered at its narrowest point, about 500 metres wide.
The Wilkins ice shelf has snapped for the first time, causing consternation at the state of the environment
This may now allow ocean currents to wash away far more of the Wilkins shelf.
David Vaughan, a glaciologist with the British Antarctic Survey, said: 'We've waited a long time to see this. My feeling is that we will lose more of the ice, but there will be a remnant to the south.'
The Wilkins, now the size of Jamaica, is one of ten shelves to have shrunk or collapsed in recent decades on the peninsula.
Cores of sediments on the seabed indicate that some of these ice shelves had been in place for at least 10,000 years
Since 1950, the ice bridge that cracked apart on Saturday had more than halved in length.
Temperatures in the Antarctic have risen by up to about 5.4f (3c) in the past 50 years, the fastest rate of warming in the Southern Hemisphere.
Antarctica's response to warming will go a long way to deciding the pace of global sea level rise.
The loss of ice shelves does not affect sea levels - floating ice contracts as it melts and so does not raise ocean levels.
But their loss can allow glaciers on land to slide more rapidly towards the sea, adding water to the oceans.
About 175 nations have been meeting in Bonn, Germany, since March 29 as part of a push to agree by the end of 2009 a new U.N. treaty to combat climate change.
Scientists say change in the Antarctic is rarely as dramatic as it has been in recent times
The U.S. is also pushing to protect Antarctica's fragile environment by imposing mandatory limits on the size of cruise ships sailing there and the number of passengers they bring ashore, minimising the likelihood of oil spills.At a conference starting today in Baltimore, U.S. diplomats will propose amending the 50-year-old international Antarctic Treaty.