Poolkappen, IJsbergen en Gletsjers #2

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Antarctic sea ice increasing: study

In recent years all the headlines have been about ice melting in some of the globe's chilliest places. But it seems that global warming may actually be leading to an increase in sea ice in parts of the Antarctic.

Scientists in the United Kingdom have produced a study which shows ice has grown by 100,000 square kilometres each decade in the past 30 years.

The increase is being put down to the hole in the ozone layer.

The British Antarctic Survey combined with NASA to look at the levels of ice in the region over the long term.

What was clear was that climate change produces complex results. Instead of a widening hole in the ozone layer, produced by human activity, warming temperatures as they have in the Arctic, in Antarctica it was having the opposite effect.

Scientists such as Julienne Stroeve from the National Snow and Ice Data Centre in the United States say they are not that surprised by the news of the study and its findings.

"There's been a change in atmospheric circulation around Antarctica related to the stratospheric ozone depletion and this actually causes stronger winds, which then pushes the ice away from the coast in some regions of Antarctica, which actually then causes more new ice formation and increases the overall sea ice in that region," she said.

"In other parts of Antarctica the temperatures have been decreasing and this is again sort of what we've expected to see, at least according to what the climate models tell us should be happening.

"But if you look at the Antarctic Peninsula for example, that's where you've had really strong warming and you've had a warming of about 3 degrees Celsius in the last 50 years.

"And if you look at changes in sea ice in that region they all show very strong negative trends.

"The paper shows an overall positive trend if you look at all of Antarctica, but there's regional differences that are quite different from different regions.

"We have to deal with what we know about warming in certain regions and changes in circulation and wind patterns in other regions."

Dr Stroeve argues that the rate of ice expansion, even as it translates to hundreds of thousands of square kilometres, is relatively insignificant.

"This recent paper shows you know a change in the annual mean ice extent of Antarctica of only 0.97 per cent per decade which is really close to zero," she added.

"In contrast if you look at the Arctic, you see statistically significantly trends of about 4 per cent per decade in the opposite direction right now if you look at the annual mean. Certainly it's a very small change for the Antarctic.

"The Antarctic is very different than the Arctic and what we're noticing is that you'll see negative trends in some areas of the Antarctic and positive trends elsewhere.

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The Wilkins Ice Shelf, on the western side of the Antarctic Peninsula, experienced multiple disintegration events in 2008. A rapid retreat started in February, near the end of the Antarctic summer. Another breakup began in May, during the Antarctic winter. And fresh cracks appeared on the shelf in late November 2008. By the beginning of 2009, a narrow ice bridge was all that remained to connect the ice shelf to ice fragments fringing nearby Charcot Island. That bridge gave way in early April 2009.
Days after the ice bridge rupture, on April 12, 2009, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite captured this image of the southern base of the ice bridge, where it connected with the remnant ice shelf. This image shows ice fragments of varying sizes mixed with ice mélange. A crack in the east reveals dark ocean water below. Although the ice bridge between the shelf and Charcot Island had played a role in stabilizing the ice fragments in the region, its rupture didn’t guarantee an immediate ice exodus. The Wilkins Ice Shelf experienced a breakup event in 1998, yet the ice blocks from that breakup froze in place for a decade.
In this image, the low angle of the Sun accentuates shadows, and highlights an interesting feature. The large slab of ice in the lower left corner of this image displays a slight linear bulge along its northeastern edge. This area of raised ice is consistent with ice shelf modeling in numerous studies.
An ice shelf is a thick slab of ice that is attached to a coastline. The seaward extension of the shelf floats on the water like sea ice. Unlike sea ice, however, ice shelves can have thicknesses in excess of 100 meters, with part of the ice front above water and part of it below. After part of an ice shelf breaks away, the remaining ice shelf, despite its thickness, doesn’t remain impervious to the change. In both ice and water, pressure increases with depth, but the pressure gradient is steeper in water. This means that ocean water tends to deform the ice, pushing inward on the ice slab’s front. On its top surface, the ice slab bulges, and its top edge rotates outward and downward. The raised area along the front of the ice slab in this image suggests that ocean water has deformed this ice slab as predicted.

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New warning over Arctic ice-cap

The Arctic ice-cap, a permanent feature for at least 100,000 years, could vanish in summertime far sooner than predicted, a leading scientist says.

Professor Peter Wadhams, from the University of Cambridge, told BBC News he has brought forward his estimates of the ice-cap's demise.

He believes the ice is now so thin that almost all of it will disappear in about a decade.

He says it will become seasonal, forming only during the winter.

He told the BBC: "By 2013 we will see a much smaller area in summertime than now, and certainly by about 2020, I can imagine that only one area will remain in summer."

His assessment is based on analysis of nearly 40 years of sonar data gathered on Royal Navy submarines patrolling beneath the ice - the first, HMS Dreadnought, was in 1971.

Until recently, most climate forecasts suggested that the Arctic Ocean would have ice-free summers only towards the end of the century.

The most extreme scenario was for the ice to retreat as soon as 2013, but that was dismissed by many as far too soon.

Now Professor Wadhams, who has studied the Arctic for the past 40 years, says that there is "almost a breakdown" in the ice-cover.

Over most of the Arctic, there has been a massive decline in the amount of so-called multi-year ice - ice that is tough enough to withstand the summer warmth.

Much of what is left of this ice accumulates in an area north of Greenland and Ellesmere Island in Canada, and may form what he calls "a last holdout, a kind of Alamo".

Professor Wadhams said: "The change is happening so fast. It's the result of this steady thinning over four decades that has brought it to a state where its summer melt is causing it to disappear.

"It's like the Arctic is covered with an egg shell and the egg shell has been thinning to the point where it is now just cracking completely."

The rest of the story continues here...

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Origin of Antarctic ice revealed

Incredible peaks and valleys, buried beneath ice for 14 million years, have revealed evidence of how the East Antarctic ice sheet first formed.

Scientists used radar to map an area of the Gamburtsev mountains - believed to be the point of origin of the ice.

The region would have been cold enough for the first glacier to form.

Writing in the journal Nature, the researchers say their findings provide important clues about how the ice sheet will behave as our climate changes.

"This is the largest reservoir of ice on Earth, and the most poorly understood place on our planet," said the British Antarctic Survey's Fausto Ferraccioli, a scientist involved in a separate international project to study the region.

He explained that the elevation and location of the Gamburtsev Mountains - in the centre of the ice sheet - made them an "ideal place" for the formation of the very first ice.

Icy unknown

Sun Bo from the Polar Research Institute of China, who led this study, has now provided further insight into the evolution of the ice sheet.

He and his colleagues travelled 1,235km (767 miles) by tractor train from a research station at the edge of East Antarctica, to the summit of Dome A of the Gamburtsev range, near the centre.

Dr Sun's team then attached radar equipment to the tractor and drove around, meticulously surveying a 30km by 30km square of the glacial region.

Their radar revealed a landscape that, 14 million years ago, looked similar to the European Alps.

"This is true scientific exploration," said Martin Siegert, head of the school of geosciences at Edinburgh University, who was also involved in the study.

"There's nothing to guide you really. Peering down at the ice sheet beneath your feet, you just don't know what's under there."

And for this type of exploration, the use of radio waves is very powerful.

When the waves reach the interface between ice and rock they bounce back, because of the difference in electrical properties between the two.

....Rest of story...

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Argentine Glacier Advances Despite Global Warming

BUENOS AIRES, Argentina — Argentina's Perito Moreno glacier is one of only a few ice fields worldwide that have withstood rising global temperatures.

Nourished by Andean snowmelt, the glacier constantly grows even as it spawns icebergs the size of apartment buildings into a frigid lake, maintaining a nearly perfect equilibrium since measurements began more than a century ago.

"We're not sure why this happens," said Andres Rivera, a glacialist with the Center for Scientific Studies in Valdivia, Chile. "But not all glaciers respond equally to climate change."

Viewed at a safe distance on cruise boats or the wooden observation deck just beyond the glacier's leading edge, Perito Moreno's jagged surface radiates a brilliant white in the strong Patagonian sun. Submerged sections glow deep blue.

And when the wind blows in a cloud cover, the 3-mile-wide glacier seems to glow from within as the surrounding mountains and water turn a meditative gray.

Every few years, Perito Moreno expands enough to touch a point of land across Lake Argentina, cutting the nation's largest freshwater lake in half and forming an ice dam as it presses against the shore.

The water on one side of the dam surges against the glacier, up to 200 feet above lake level, until it breaks the ice wall with a thunderous crash, drowning the applause of hundreds of tourists.

"It's like a massive building falling all of the sudden," said park ranger Javier D'Angelo, who experienced the rupture in 2008 and 1998.

The rupture is a reminder that while Perito Moreno appears to be a vast, 19-mile-long frozen river, it's a dynamic icescape that moves and cracks unexpectedly.

"The glacier has a lot of life," said Luli Gavina, who leads mini-treks across the glacier's snow fields.