INTERVIEW - New Antarctic iceberg split no threat-scientist
Date: 20-May-02
Country: AUSTRALIA
Author: Michael Byrnes
The latest breakoff from the Ross Shelf, known as C-19, is 200 kilometres long by 31 kilometres wide and covers an area of almost 3,900 square kilometres.
"It almost completes the breakoff of the ice between Roosevelt Island and McMurdo. That takes it (the shelf) back a lot closer to where the 1902 edge was. It's like a 100 year event," Bill Budd, Professor of Meteorology at the Antarctic Cooperative Research Centre (CRC) told Reuters from Hobart.
The latest iceberg and another smaller iceberg about half its size which split from the Ross Shelf a week earlier both resulted from normal "calving", as thick layers of ice gradually slide down the high Antarctic plateau.
In contrast, climate warming has been blamed for causing the break-up of ice shelves on the Antarctic Peninsula, which juts out toward the southern tip of South America.
The latest breaks had been monitored for some time and were expected, Budd said.
"You can see the large rifts developing back where the calving takes place. Those rifts correspond to that earlier position where the front was back at the beginning of last century," he said.
ANTARCTIC COINCIDENCE
Budd said it was coincidental that big breaks were occurring from the Ross Shelf at the same time as major climate-related breaks from the Peninsula.
The latest break completed a series of big splits from the Ross Shelf that began in 1987. "There's not much left of that large advance to break off," Budd said. "This last one was such a large piece that it's taken most of the advanced ice back for the whole stretch of that width of the ice shelf."
Antarctic ice moves forward at 400 to 900 metres a year, taking 100 years to grow the 30-40 kilometres into the sea which typically break off.
The huge bergs now drifting in Antarctic waters were unlikely to pose a threat to shipping. "But they can be a nuisance value," Budd said.
Icebergs from recent breaks were now drifting in the McMurdo area, affecting Antarctic shipping lanes and also the ocean circulation in the area, he said.
The icebergs would not drift as far north as Sydney, but could drift for years in the Ross Sea, following an uncertain route.
If they became caught in the circumpolar flow, which would take them toward South America, they would not last more than a year before breaking up and melting before reaching the Drake Passage, between the southern tip of South America and the Antarctic Peninsula, Budd said.
It they followed the Antarctic coast westward they could stay in cold water for up to 10 years.
"Icebergs don't go as far north these days... partly because of global warming.... as more than 100 years ago," he said.
Unlike 100 years ago, it was unlikely icebergs would drift as far north as New Zealand. Westward floating icebergs could get as far as 90 degrees east, between Western Australia and South Africa. This would steer them north toward Heard Island where a stream could carry them toward Macquarie Island, south of New Zealand, he said.
"That's a long way south of us still," he said.
