Page last updated at 15:09 GMT, Friday, 26 February 2010

Vast Antarctic iceberg 'threatens marine life'

How the new iceberg was formed

Satellite image of the Mertz Glacier, plus graphic comparing size of London with size of new iceberg
7 January 2010: B9B iceberg, which is 97km long, approaches the Mertz Glacier tongue.
Satellite image of the Mertz Glacier, plus graphic comparing size of London with size of new iceberg
7 February 2010: the B9B iceberg makes contact with the tongue, which already had major rifts in it.
Satellite image of the Mertz Glacier, plus graphic comparing size of London with size of new iceberg
20 February 2010: the Mertz Glacier tongue breaks off creating another massive iceberg.
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A vast iceberg that broke off eastern Antarctic earlier this month could disrupt marine life in the region, scientists have warned.

They say the iceberg, which is 78km long and up to 39km wide, could have consequences for the area's colonies of emperor penguins.

The emblematic birds may be forced to travel further afield to find food.

The iceberg calved from the Mertz Glacier Tongue after it was hit by another huge iceberg, called B9B.

"It is a very active area for algae growth, especially in springtime," explained Dr Neal Young from the Australia-based Antarctic Climate and Ecosystems Co-operative Research Centre.

Iceberg 'size of Luxembourg' threat

"There are emperor penguin colonies about 200-300km away to the west. They come to this area to feed, and seals in the area also come to get access to the open water," he told BBC News.

He suggested that a change in the availability of open water could affect the rate of food production, which would have an impact on the amount of wildlife it could sustain.

"If the area gets choked up (with ice), then they would have to go elsewhere and look for food."

Changing landscape

The calving of the iceberg, which has an estimated mass of 700-800bn tonnes, has changed the shape of the local geography, Dr Young explained.

Large icebergs always attract a lot of attention due to their scale
Dr Mike Meredith,
British Antarctic Survey

"We have got two massive icebergs that - end to end - create a fence of about 180km.

"So the area's geography has changed from a situation where we effectively had a box in which two sides were open ocean," he told BBC News.

"Now we have a fence across one side of the box."

Before the formation of the iceberg, the Mertz Peninsula provided the right conditions for a polynia - an expanse of open water surrounded by sea-ice - to exist.

"Winds blow off the coast and clear anything in that region, including sea ice, exposing open water," Dr Young explained.

He added that as well as providing a feeding site for the region's wildlife, the polynia also was a key production site of "bottom water"; very cold, dense water that sinks to the ocean floor.

"Sea ice is relatively fresh compared to sea water, so the more sea ice you have (in the surrounding area), the more salt that is left in the remaining open water."

The rise in the concentration of salt increases the water's density, causing it to sink to the bottom of the ocean.

"This area around the Antarctic coastline, of which the Mertz Peninsula is one part, produces about one quarter of the Antarctic's bottom water, but the Mertz polynia is a major contributor," Dr Young said.

He added that the new iceberg had shortened the length of the Mertz Glacier Tongue, which could result in pack ice entering the area and disrupting the polynia.

"That means that the bottom water production rate... will decrease.

"The bottom water spills over the continental shelf, flows down the continental slope into the deep ocean."

This process helps drive the "conveyor belt" of currents in the Southern, Pacific and Atlantic Oceans.

Any disruption to the net flow of bottom water could result in a weakening in the deep ocean circulation system, which plays a key role in the global climate system.

'Natural laboratory'

However, the researchers say the changes to the region triggered by the formation of the new iceberg will not shut down the circulation system or affect the world's climate.

"Large icebergs always attract a lot of attention due to their scale," observed Dr Michael Meredith from the British Antarctic Survey, who was not involved in the research.

"Bottom water is indeed an important part of the global ocean overturning circulation and hence climate," he told BBC News.

"There are also a number of other locations of bottom water formation, however. So, it's unlikely that a large-scale sustained change of the order of magnitude required for a global climate impact will happen from this one event.

"The more important thing, I think, is that this event has been closely and carefully monitored by scientists, who will now look at the processes whereby such calvings can impact on the ocean and the ecosystem - and studying this natural laboratory will add to our knowledge of how the Antarctic system works."



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