Ice shelf breaks up

Tenth mass to recede or float away since 1950

European Space Agency

BREAKING UP: A satellite image of the early stage of the disruption of the ice bridge that connects the Wilkins Ice Shelf to Charcot and Latady Islands. The first rifts occured about seven hours after this image was taken.

PRECARIOUS: A 20 metre-high ice cliff forming the edge of the Wilkins Ice shelf on the Antarctic Peninsula is seen from a plane in January.

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The collapse of a crucial "hinge" section of an Antarctic ice shelf the size of Hawke's Bay is likely to create huge icebergs that could eventually head for New Zealand.

Satellite images of the Wilkins Ice Shelf, a plate of floating ice on the southwest Antarctic Peninsula, which stretches toward South America, show a 40km-long strip of ice holding it in place snapped at its narrowest point on Saturday.

Tim Naish, of Victoria University's Antarctic Research Centre, said scientists advised that the "pinning point" of the ice shelf to the land was pretty critical in keeping the shelf stable and "once it goes, the ice shelf itself is likely to completely disappear".

Angelika Humbert from Muenster University's Institute of Geophysics, has monitored daily satellite photos of the area where the ice bridge connects it to Charcot and Latady islands.

"In the past months, we have observed the ice bridge deforming and its narrowest location acting as a kind of hinge," Dr Humbert said.

Professor Naish said the shelf would probably break up and travel along the Antarctic circumpolar current to eastern New Zealand and the Pacific Ocean.

"That's when we see these icebergs, like the ones we saw ... [in 2006]."

The icebergs could take up to two years before they reached New Zealand, if they were big enough and got caught up in the right currents, and could be about the same size as those that drifted up the east coast of the South Island in 2006.

The 14,000 square kilometre Wilkins Ice Shelf has now become the 10th Antarctic ice shelf to recede or float away since 1950.

The Antarctic peninsula had experienced 2 1/2 degrees of warming in the past 50 years, making it "one of the hot spots on the planet", Professor Naish said.

"It's a consequence of global warming. Antarctica is behaving in a very strange way, bits of it are cooling and bits of it are warming. Our deep time records tell us that these ice shelves are the early warning signals; when they go, then we see quite dramatic and unstable changes in the ice sheets and glaciers feeding them."

Scientists believe the ice shelf have been in place for thousands of years.

Professor Naish said the breakdown of the Wilkins shelf would not contribute to rising sea levels, because it was already floating. "It's like an ice cube in a glass of water when the cube melts, the water level does not go up."

But as the ice shelves disappeared, it could cause connected glaciers and ice on the land mass to melt and flow into the ocean more quickly, which would raise sea levels, he said.

- © Fairfax NZ News