Mammoth iceberg 'could alter ocean circulation'

Marlowe Hood Yahoo News 26 Feb 10;

PARIS (AFP) – An iceberg the size of Luxembourg knocked loose from the Antarctic continent earlier this month could disrupt the ocean currents driving weather patterns around the globe, researchers said.

While the impact would not be felt for decades or longer, a slowdown in the production of colder, dense water could result in less temperate winters in the north Atlantic, they said Thursday.

The 2,550 square-kilometre (985 square-mile) block broke off on February 12 or 13 from the Mertz Glacier Tongue, a 160-kilometer spit of floating ice protruding into the Southern Ocean from East Antarctica due south of Melbourne, researchers said.

Some 400 metres (1,300 feet) thick, the iceberg could fill Sydney Harbour more than 100 times over.

It could also disturb the area's exceptionally rich biodiversity, including a major colony of emperor penguins near Dumont d'Urville, site of a French scientific station, according to the scientists.

"The ice tongue was almost broken already. It was hanging like a loose tooth," said Benoit Legresy, a French glaciologist who has been monitoring the Metz Glacier via satellite images and on the ground for a decade in cooperation with Australian scientists.

The billion-tonne mass, 78 kilometres long and half-again as wide, was dislodged by another, older iceberg, known as B9B, which split off in 1987.

Jammed against the Antarctic continent for more than 20 years, B9B smashed into the Metz tongue like a slow-motion battering ram after it began to drift.

Both natural cycles and man-made climate change contribute to the collapse of ice shelves and glaciers.

Tide and ocean currents constantly beat against exposed areas, while longer summers and rising temperatures also take a toll.

"Obviously when there is warmer water, these ice tongues will become more fragile," said Legresy, who works at the Laboratory for Geophysics and Oceanographic Space Research in Toulouse, southern France.

The Metz Glacier Tongue, fitted with GPS beacons and other measurement instruments, could provide crucial insights into how these influences should be apportioned.

"For the first time, we will have a detailed record of the full cycle of a major calving event -- before, during and after," he said.

"We are using the ice tongue as a laboratory to study the processes that might be impacted by climate change, including calving, ocean temperature, sea level change."

Since breaking off, the iceberg -- along with the newly mobile B9B, which is about the same size -- have moved into an adjoining area called a polynya.

Distributed across the Southern Ocean, polynyas are zones that produce dense water, super cold and rich in salt, that sinks to the bottom of the sea and drives the conveyor-belt like circulation around the globe.

If these icebergs move east and run aground, or drift north into warmer climes, they will have no impact on these currents.

"But if they stay in this area -- which is likely -- they could block the production of this dense water, essentially putting a lid on the polynya," Legresy explained.

The Metz Glacier Polynya is particularly strong, and accounts for 20 percent of the "bottom water" in the world, he added.

Eventually, the icebergs will die a natural death, but their lifespan depends on where they go.

Adrift, they could melt in a couple of decades. If they remain lodged against the Antarctic landmass, they could persist far longer.

Vast Antarctic iceberg 'threatens marine life'
BBC News 26 Feb 10;

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.

"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."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."

Giant iceberg breaks off from Antarctic glacier
Reuters 27 Feb 10;

SINGAPORE (Reuters) - An iceberg the size of Luxembourg has broken off from a glacier in Antarctica after being rammed by another giant iceberg, scientists said on Friday, in an event that could affect ocean circulation patterns.

The 2,500 sq km (965 sq mile) iceberg broke off earlier this month from the Mertz Glacier's 160 km (100 miles) floating tongue of ice that sticks out into the Southern Ocean.

The collision has since halved the size of the tongue that drains ice from the vast East Antarctic ice sheet.

"The calving itself hasn't been directly linked to climate change but it is related to the natural processes occurring on the ice sheet," said Rob Massom, a senior scientist at the Australian Antarctic Division and the Antarctic Climate and Ecosystems Cooperative Research Center in Hobart, Tasmania.

Both organizations, along with French scientists, have been studying existing giant cracks in the ice tongue and monitored the bumper-car-like collision by the second iceberg, B-9B.

This 97 km long slab of ice is a remnant of an iceberg of more than 5,000 sq km that broke off, or calved, in 1987, making it one of the largest icebergs ever recorded in Antarctica.

The Mertz glacier iceberg is among the largest recorded for several years. In 2002, a iceberg about 200 km long broke off from Antarctica's Ross Ice Shelf. In 2007, a iceberg roughly the size of Singapore broke off from the Pine Island Glacier in West Antarctica.

Massom said the shearing off of the ice tongue and the presence of the Mertz and B-9B icebergs could affect global ocean circulation.

The area is an important zone for the creation of dense, salty water that is a key driver of global ocean circulation. This is produced in part through the rapid production of sea ice that is continually blown to the west.

"Removal of this tongue of floating ice would reduce the size of that area of open water, which would slow down the rate of salinity input into the ocean and it could slow down this rate of Antarctic bottom water formation," he said.

He said there was a risk both icebergs would become grounded on banks or shoals in the area, disrupting the creation of the dense, salty water and the amount that sinks to the bottom of the ocean, he said.

Oceans act like a giant flywheel for the planet's climate by shifting heat around the globe via myriad currents above and below the surface.

(Reporting by David Fogarty; Editing by Alex Richardson)

Iceberg breaks in Antarctica not where expected
Seth Borenstein, Associated Press Yahoo News 27 Feb 10;

WASHINGTON – With the dramatic crash of an iceberg against a glacier that dislodged a massive new chunk of ice, the mysterious continent of Antarctica once again did the unexpected.

A big chunk of ice, slightly smaller than Oahu, broke off from a place it wasn't supposed to and in a way that wasn't quite anticipated, scientists reported Friday.

The new iceberg broke off from the cooler eastern end of Antarctica, the result of tidal forces that caused a longer but thinner iceberg that stretches for 60 miles to hammer it free. The new chunk broke off a long tongue of ice that had been building for decades, but will unlikely cause future ice loss problems on the continent, scientists said.

This happened as researchers have focused attention on the western side of Antactica, a continent about 1 1/2 times larger than the United States. Concern has grown over warmer temperatures there and especially the region's shrinking peninsula, which sticks out into the water like a broken pinky finger.

Remarkably, that peninsula, where last year one ice shelf was said to be hanging by a thread, has had an unusually cool summer. It's hit pause on ice loss, said Ted Scambos, senior scientist with the National Snow and Ice Data Center.

In a satellite phone interview this week from the western peninsula where he's working, Scambos predicted no major ice calving. His comments were made Thursday.

The next day Australian researchers alerted the world to the iceberg crash with the Mertz Glacier on the other side of the continent. They said it had probably occurred around Feb. 12 or 13.

"There are some crazy things going down in Antarctica," said Mark Serreze, director of the snow and ice data center, based in Boulder, Colo. "It seems kind of weird, but weird things happen."

Scientists have been tracking global warming's influence in Antarctica, a place more complicated than the Arctic. Scambos was placing instruments on the dwindling Larsen ice shelf in the peninsula to measure its disintegration in a scientific version of a deathwatch.

The ice loss that happened a couple of weeks ago was not due to global warming, but a natural process taking place in a region that has been relatively stable over the years.

For decades the tongue of the Mertz Glacier in the eastern part of the continent has grown further out into the water until it was about 60 miles long by 18 miles wide, said Benoit Legresy, a researcher with the LEGOS laboratory for geophysical studies in Toulouse, France.

Then an iceberg called B9B, which had broken off from another part of Antarctica in 1987, came by and "gave it a pretty big nudge," said Australian Antarctic Division glaciologist Neal Young.

"It was a slow process," Legresy said. He said B9B was "sitting there, it must have been pushed and pulled by the current every day and used as a hammer to bang on the other one by the ocean currents."

The dislodging occurred because of the iceberg's latest location and water that had warmed during Antarctica's summer, leaving less sea ice, Legresy said.

This happened "behind our backs," said NASA glaciologist Robert Bindschadler. "It's a good thing to be reminded that it's not all about west Antarctica."

Tongues like the one on the Mertz "ultimately are going to have to break off, making some big pieces of ice, and the ocean moves them around and occasionally they get in each other's way," Bindschadler said.

A couple scientists worried that this region around the Antarctic coast could fill with sea ice, which would disrupt the sinking ability of the dense and cold water. This sinking water is what spills into ocean basins and feeds the global ocean currents with oxygen, said Steve Rintoul, an oceanographer at Australia's national science agency. The fear is that it could starve areas of oxygen.

But other scientists from NASA, Penn State and the British Antarctic Survey said that's not a very likely scenario and not to worry.

"Icebergs whacking each other has happened for millions of years and life is still down there and pretty robust," NASA's Bindschandler said.

More than anything, it's a shift from the usual worries about Antarctic ice.

Data and new detailed maps from the U.S. Geological Survey, the British Survey and the snow and ice data center show that the western Antarctic peninsula has been shrinking noticeably. Since the first measurements were made more than 50 years ago, the peninsula has lost about 8,000 square miles of ice — slightly less than the size of New Jersey — said USGS scientist Jane Ferrigno. The peninsula itself is about the size of Montana.

And every ice shelf on that peninsula has shrunk, with the losses accelerating since the 1990s, Ferrigno said.

"It may be a red flag about what may be happening in the future if this warming continues," Ferrigno said. "This is way beyond anything we've seen before" in centuries of ice core data.

With that in mind, snow and ice data center's Scambos and a team of researchers put measuring devices all over the threatened Larsen ice shelf, where he said "it does look like it's an ice shelf that's really in its last years of existence."

But it won't disappear this year, he said.

Cooler-than-normal temperatures have paused the melt, Scambos said, a development he views as only temporary. "There's no big recovery in progress."