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Antarctic iceberg A-68
Topic Started: 17 Jan 2017, 12:38 AM (169 Views)
skibboy
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Ice crack to put UK Antarctic base in shut-down

By Jonathan Amos
BBC Science Correspondent

6 hours ago

Posted Image
Aurora: Halley base has become a centre for the study of space weather

The British Antarctic Survey is to pull all staff out of its space-age Halley base in March for safety reasons.

The highly unusual move is necessary because the Brunt Ice Shelf on which the research station sits has developed a big new crack.

BAS officials say neither staff nor the base are in any immediate danger but believe it would be prudent to withdraw while the situation is assessed.

The plan would be to go back once the Antarctic winter is over, in November.

Halley station comprises a series of hi-tech pods that are mounted on hydraulic legs and skis so that they can be moved periodically further inland, to get away from the shelf edge where icebergs are calved into the ocean.

Unpredictable situation

BAS is in the process of conducting such a move right now.

The relocation is all but complete, with the last pod currently in the final stage of being shifted 23km to the new site.

The move was necessitated by a chasm that had opened up in the shelf and which threatened to cut off Halley.

But this huge fissure to the west of the station is not the cause of the temporary closure.

Rather, it is another break in the ice some 17km to the north and east of the new base position.

It has been dubbed the "Halloween Crack" because it was discovered on 31 October.

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"Changes to the ice, particularly the growth of a new crack, presents a complex glaciological picture that means that BAS scientists are unable to predict with certainty what will happen to the ice shelf during the forthcoming Antarctic winter," the research organisation said in a statement.

"As a precautionary measure, BAS will remove its people before the Antarctic winter begins."

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Broadly speaking, "north" is towards the top-left of this graphic

The organisation says it does not believe the ice shelf is about to experience a major calving event, but make the point that if something were to happen it would be very difficult to react in the depths of an Antarctic winter.

"What we've decided is that given the unpredictability, combined with our inability to do anything about it in winter - no aircraft in the continent, it's dark, it's very cold; all those kinds of issues - then actually the prudent thing to do is withdraw our staff, close the station down in a controlled manner and then go back in next summer," BAS director of operations Captain Tim Stockings told BBC News.

Together with the Rothera base on the Antarctic Peninsula, Halley spearheads the UK presence - and scientific activity - on the White Continent.

Halley gathers important weather and climate data, and it played a critical role in the research that identified the ozone "hole" in 1985.

In recent years, Halley has also become a major centre for studying solar activity and the impacts it can have on Earth.

This is most evident in the beautiful auroras that form over the base - the consequence of particles from the Sun crashing into air molecules high in the atmosphere.

Flying the flag

Just under 20 permanent staff reside at Halley.

In winter, they would watch over experiments.

BAS now has to decide if any of those experiments can be left running autonomously, or whether it is better to just shut everything down.

Scientists have placed sensors on either side of the more than 40km-long Halloween Crack so that they can monitor its status.

"Obviously, we'll seek to get out of those whatever we can; we'll also be using satellite imagery over the winter as well. Then, next season we'll send a team in to re-open the station, verify the measurements from our instruments and take the situation from there," explained Captain Stockings.

"But I should say - we are committed to our presence in that part of the British Antarctic Territory and to the science we do there. Absolutely.

"We've spent a long time finding the new site for Halley VI and of itself this site isn't directly at risk - it's just the unpredictability of the whole area."

Posted Image
The chasm to the west prompted the move but it is not the reason for the winter shut-down

Source: Posted Image
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skibboy
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Larsen ice crack continues to open up

By Jonathan Amos
BBC Science Correspondent

20 January 2017

Posted Image

The crack that looks set to spawn a giant iceberg in the Antarctic has continued to spread.

The rift in the Larsen C Ice Shelf has grown a further 10km since 1 January.

If the fissure propagates just 20km more, it will free a tabular berg one-quarter the size of Wales.

That would make it one of the biggest icebergs ever recorded, according to researchers at Swansea and Aberystwyth universities, and the British Antarctic Survey.

News of the lengthening crack in the 350m-thick floating ice shelf on the eastern side of the Antarctic Peninsula comes from the EU’s Sentinel-1 satellite system.

Comprising two spacecraft, this orbiting capability can continuously monitor Larsen C no matter what the weather is doing because its radar sensors see through cloud.

Their data indicates the fissure now extends for some 175km.

But just how long it will take before the 5,000 sq km block finally breaks free is anyone’s guess, says Swansea's Prof Adrian Luckman.

"The rift tip has just entered a new area of softer ice, which will slow its progress," he told BBC News.

"Although you might expect any extension to hasten the point of calving, it actually remains impossible to predict when it will break because the fracture process is so complex.

"My feeling is that this new development suggests something will happen within weeks to months, but there is an outside chance that further growth will be slow for longer than that.

"Sometimes rift growth is triggered by ocean swell originating elsewhere, which is also hard to predict."

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Images taken in November last year illustrate the scale of the rift

When the berg splits away, interest will centre on how the breakage will affect the remaining shelf structure.

The Larsen B Ice Shelf further to the north famously shattered following a similar large calving event in 2002.

The issue is important because floating ice shelves ordinarily act as a buttress to the glaciers flowing off the land behind them.

In the case of Larsen B, those glaciers subsequently sped up in the absence of the shelf.

And it is the land ice - not the floating ice in a shelf - that adds to sea level rise.

If Larsen C were to go the same way it would continue a trend across the Antarctic Peninsula.

In recent decades, a dozen major ice shelves have disintegrated, significantly retreated or lost substantial volume - including Prince Gustav Channel, Larsen Inlet, Larsen A, Larsen B, Wordie, Muller, Jones Channel, and Wilkins.

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How the rift appeared to Sentinel-1 at the beginning of the month

Another development to watch will be the behaviour of the free floating berg, and its progress away from the Antarctic.

"Sea ice in the region circulates clockwise with the Weddell Gyre, rather than remaining in one place, and icebergs can be carried with this, sometimes out into the Southern Ocean," explained Prof Luckman.

"It all rather depends on how soon the iceberg breaks up, and how the iceberg draft compares with ocean depths.

"Ocean depths are not perfectly known in the region precisely because the near continuous ice cover makes ship operations difficult."

Many of the big tabular bergs produced in this region of the Antarctic get swept up in currents that eventually take them north towards the British overseas territory of South Georgia.

There, they can be caught in shallow waters to gradually wither away.

This ocean conveyor is the same one exploited by Ernest Shackleton to get his crew to safety when their ship, the Endurance, was crushed in thick sea-ice in the Weddell Sea in 1916.

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The remnants of many such bergs end up at South Georgia

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The mighty A-38 berg reached South Georgia after six years of drifting

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UK completes Antarctic Halley base relocation

By Jonathan Amos
BBC Science Correspondent

2 February 2017

Posted Image
All eight modules were towed across the ice shelf to the new location further from the sea

The British Antarctic Survey (BAS) has completed the move of its Halley research station.

The base is sited on the floating - and moving - Brunt Ice Shelf, and had to be relocated or face being dumped in the ocean.

Tractors were used to tow the eight modules that make up the futuristic-looking Halley 23km further "inland".

Last month, BAS announced it would "mothball" the station for the duration of the coming Antarctic winter.

The decision was made after a new crack opened in the ice shelf.

This fissure is a long way (17km) from Halley's new position but it has prompted some concern about the stability of the whole area.

Glaciologists want more time to assess the situation, and safety considerations demand staff be withdrawn before deteriorating weather conditions and 24-hour darkness make access and egress extremely difficult.

Halley's move was facilitated by its novel design.

The base has a hydraulic leg and ski system that allows it to be raised above the annual snowfall, and periodically shifted.

If these adjustments were not to happen, the station would eventually be buried and carried to the shelf edge where it would then be dropped into the ocean inside an iceberg.

Halley bases I to IV were abandoned to this fate.

The new design makes any adjustments easier and less labour intensive.

"The relocation has gone really well," BAS director of operations Captain Tim Stockings told BBC News.

"When you consider the big red module, which contains the general living and recreation space, weighs over 200 tonnes, I'm sure you can understand what a big exercise this is.

"And, yes, we plan it really well, but until you see these things actually move, you're always going to be a little nervous."

And the head of BAS, Prof Dame Jane Francis, added: "The relocation is a terrific achievement for our operational teams. Everyone who has worked so hard is absolutely buoyant about the success of the move."

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The move was made possible by a hydraulic leg and ski system

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The central red module weighs over 200 tonnes

The UK has operated a research station on the 150m-thick Brunt Ice Shelf since the late 1950s.

It has two key functions.

One is as a support link to deep-field exploration of the Antarctic interior.

And the second - and main task - is as a centre of research itself.

Scientists at the base have an international reputation for their studies of Earth's atmosphere.

It was at Halley, for example, that a BAS-led team was able to show in 1986 that a hole had opened in the ozone layer.

Present day work also includes investigations into "space weather" - the impacts that occur when particles and magnetic fields billowing away from the Sun collide with Earth's magnetic field and upper atmosphere.

Solar storms are known to disrupt the operation of satellites and can even interfere with electricity grids on the ground.

___________________________________________________________________________________________________________________________________________________________________


Halley base and a tale of two fissures

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Broadly speaking, "north" is towards the top-left of this graphic

- The floating Brunt Ice Shelf flows seaward at a rate of 0.4km per year

- Unless Halley were moved it would eventually be lost to the ocean

- An opening chasm to the west threatened to cut the base off

- The just-completed relocation has put the station in a safe place

- But a new crack - dubbed "Halloween Crack" - has opened to the north

- It poses no immediate danger, but glaciologists need time to study it

- A winter shutdown will occur at Halley while the assessment is done

___________________________________________________________________________________________________________________________________________________________________


BAS is now in the process of reorganising all this research to take account of the forthcoming shutdown.

Although automatic weather stations can continue to collect their data on solar and battery energy, pretty much all other experiments will have to be suspended.

Prof Richard Horne is head of the space weather and atmosphere team at BAS.

"We're going to lose some of our data streams which go into our space weather forecasting model," he told BBC News. "Fortunately, we've built that model in such a way that it's robust and we can still operate.

"So, we'll continue to issue our forecasts, but it's going to make it more difficult to interpret what's going on.

"To give you an example - just this morning we were detecting on our magnetometer at Halley two sub-storms - there's a global disruption of the Earth's magnetic field going on.

"When the power goes off, it's going to stop that kind of monitoring."

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It has taken 13 weeks to get the base to its new position on the shelf

BAS is gradually winding down the base with the aim of having everyone out come March.

Summer-only staff who have assisted with the move are returning home onboard the Royal Research Ship Ernest Shackleton.

Of the 16 people who would ordinarily expect to over-winter at Halley, three will now work out of the UK's Rothera station on the Antarctic Peninsula instead.

Another individual will go to King Edward Point station on South Georgia.

All the others will come back to BAS HQ in Cambridge.

Halley will be re-opened in November - the start of the next summer season.

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Aurora: Halley base has become a centre for the study of space weather

Posted Image
The chasm to the west prompted the move but it is not the reason for the winter shutdown

Posted Image

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Antarctic ice crack takes major turn

By Jonathan Amos
BBC Science Correspondent

4 hours ago

Posted Image

There has been an important development in the big crack cutting across the Larsen C Ice Shelf in Antarctica.

The fissure, which threatens to spawn one of the biggest bergs ever seen, has dramatically changed direction.

"The rift has propagated a further 16km, with a significant apparent right turn towards the end, moving the tip 13km from the ice edge," said Swansea University's Prof Adrian Luckman.

The calving of the berg could now be very close, he told BBC News.

Although he also quickly added that nothing was certain.

The fissure currently extends for about 200km in length, tracing the outline of a putative berg that covers some 5,000 sq km - an area about a quarter of the size of Wales.

The crack put on its latest spurt between 25 May and 31 May.

These dates were the two most recent passes of the European Union's Sentinel-1 satellites.

Their radar vision is keeping up a constant watch as the White Continent moves into the darkness of deep winter.

After some initial activity at the beginning of the year, the Larsen crack became stationary as it entered what is termed a "suture" zone - a region of soft, flexible ice.

But this situation held only until the beginning of May, when the rift tip then suddenly forked.

And it is the new branch that has now extended and turned towards the ocean.

When the berg's calving does finally take place, the block will likely drift away quite gradually from the ice shelf.

"It's unlikely to be fast because the Weddell Sea is full of sea-ice, but it'll certainly be faster than the last few months of gradual parting. It will depend on the currents and winds," explained Prof Luckman.

Taking out such a large chunk of ice would mean the Larsen C shelf would lose more than 10% of its area.

Previous research by the Swansea group has shown that this will put the shelf in a much less stable configuration.

Similar calving events on the more northerly Larsen A and Larsen B ice shelves eventually led to their total break-up.

Scientists are concerned that this same fate could now await Larsen C.

Were the shelf to collapse (and even if it did, it would still take many years to complete), it would continue a trend across the Antarctic Peninsula.

In recent decades, a dozen major ice shelves have disintegrated, significantly retreated or lost substantial volume - including Prince Gustav Channel, Larsen Inlet, Larsen A, Larsen B, Wordie, Muller, Jones Channel, and Wilkins.

Prof Luckman's MIDAS Project is posting updates on the Larsen crack on its blog, and on its Twitter feed.

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Antarctic base waits on 'Halloween' ice crack

By Jonathan Amos
BBC Science Correspondent

7 June 2017

Restricted operations at the British Antarctic Survey's Halley station may have to continue for some time to come.

The base, which ordinarily stays open year-round, is currently closed because of uncertainty over a developing crack in the ice shelf on which it sits.

Scientists are using automated ground instruments and satellites to monitor the fissure from afar, and plan to reoccupy Halley from November.

Whether that is just for the length of the Summer season, though, is unclear.

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Halley serves as a support link to exploration in the Antarctic interior. It is also renowned for its atmospheric research

"That decision will have to be based on our observations; and these processes, because they are ice-related, are often painstakingly slow," BAS glaciologist Jan De Rydt told BBC News.

The UK has had a permanent presence on the Brunt Ice Shelf since 1956, and scientists would be loath to see their operations routinely reduced to just a few months a year.

Halley VI, as the base is known in its latest incarnation, will feature in a colourful BBC Horizon documentary on Wednesday.

Filmmaker Natalie Hewit spent three months at the turn of the year recording the huge effort to shift the station's futuristic-looking buildings to a new location.

Tractors dragged the eight modules a further 23km from the ocean's edge, to put them in a more secure spot.

"It was an incredible sight," recalled Natalie. "We have some amazing drone shots, taken from up high, of one of these blue modules moving across the ice, but you can't see where it is going because this place is so expansive, so huge, so desolate - all the way to the horizon is just white. And it really reminds you how teeny-weeny we are.

"This programme, though, is about more than just moving some buildings; it's very much about the people who work at the end of the world to do their science."

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Natalie Hewit spent three months recording life at the "end of the world"

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The move was made possible by a hydraulic leg and ski system

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Scientists are keen to return to year-round operations - but they will be led by the ice observations

Halley base is geared up to be mobile.

It has a hydraulic leg and ski system that allows it to be raised above the annual snowfall, and towed.

Without this mechanism, the station would eventually be buried and carried to the shelf edge where it would then be dropped into the ocean inside an iceberg.

Halley bases I to V were abandoned to this fate or demolished.

The latest design represents a novel solution, and the recent move was its first implementation.

The relocation was initially ordered because some long-dormant chasms in the Brunt Ice Shelf to the south and west of Halley had started lengthening again.

This turned out to be serendipitous because a completely different fissure system then opened to the east.

This new crack - dubbed the Halloween Crack because it was first discovered on 31 October last year - propagated rapidly and now extends for about 60km.

It poses no immediate threat to Halley but the uncertainties surrounding its likely future behaviour are what prompted the temporary withdrawal of staff.

This was seen as a sensible precaution given the dangers of trying to fly planes in and out of the base during the polar winter, when nights are long and weather conditions deteriorate.

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BAS experts now have to decide whether November's returning teams can once again take up permanent residence or limit their stay to just the length of the southern summer.

The Halloween Crack is propagating roughly eastwards, broadly parallel to the continent, and away from Halley.

It is the other end, though, close to the ocean, that is concentrating minds.

This tip is currently held up at a location known as the McDonald Rumples - a raised area of seafloor that catches on the bottom of the floating ice shelf.

Dr De Rydt explained: “The Brunt Ice Shelf is pinned at the rumples; it's where the shelf runs aground. The rumples are an anchor point that keeps everything in place and stable."

Glaciologists are waiting to see if the crack will break past the rumples, and on which side.

They should then get a clearer idea of the longer term reaction of the shelf to the changes that are presently in play.

Ultimately, the Halloween fissure will probably calve a huge iceberg into the ocean.

"In the 1970s, we had a similar event where a crack happened very close to where we see Halloween Crack today," Dr De Rydt told BBC News.

"That crack ended another 20km or so towards the east of where the tip of Halloween is now. And that created a berg of several thousand square kilometres."

Halley's mobility means it should not be anywhere near this great block of ice when it cuts free.

Posted Image
Halloween Crack is monitored by automatic in-situ instruments and by satellites

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A Giant Iceberg the Size of Delaware is About to Break Off Antarctica

June 21, 2017 by Reuters

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A close-up of the rift on the Larsen C ice shelf. Credit: NASA, John Sonnta

By Alister Doyle OSLO, June 21 (Reuters) – One of the biggest icebergs on record is like a “niggling tooth” about to snap off Antarctica and will be an extra hazard for ships around the frozen continent as it breaks up, scientists said on Wednesday.

An area of the Larsen C ice shelf, about as big as the U.S. state of Delaware or the Indonesian island of Bali, is connected by just 13 km (8 miles) of ice after a crack has crept about 175 kms along the sheet, with a new jump last month.

“It’s keeping us all on tenterhooks,” Andrew Fleming, of the British Antarctic Survey, told Reuters of the lengthening and widening rift, adding “it feels like a niggling tooth” of a child as it comes loose.

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Picture: the current location of the rift on Larsen C, as of May 31 2017. Labels highlight significant jumps. Credit: MIDAS project, A. Luckman, Swansea University

Ice shelves are flat-topped areas of ice floating on the sea at the end of glaciers.

The Larsen C ice is about 200 meters (656 ft) thick with about 20 meters jutting above the water.

Big icebergs break off Antarctica naturally, meaning scientists are not linking the rift to man-made climate change.

The ice, however, is a part of the Antarctic peninsula that has warmed fast in recent decades.

“There is no other evidence of change on the ice shelf. This could simply be a single calving event which will then be followed by re-growth,” Adrian Luckman, a professor at the University of Swansea in Wales, told Reuters.

His team reckons the ice will break off within months, perhaps in days or weeks.

RISKS FOR SHIPPING

The ice, about 5,000 square kilometers (1,930 square miles), will add to existing risks for ships as it breaks apart and melts.

The peninsula is outside major trade routes but the main destination for cruise ships visiting from South America.

In 2009, more than 150 passengers and crew were evacuated after the MV Explorer sank after striking an iceberg off the Antarctic peninsula.

Fleming said the Larsen C iceberg would add an extra pulse of ice and would be hazardous especially if smaller chunks reached usually ice-free areas in the South Atlantic, rather than staying close to Antarctica’s coast.

The Larsen B ice shelf nearby broke up in 2002 and some of the ice drifted into the South Atlantic towards the island of South Georgia, east of Argentina.

In 2000, the biggest iceberg recorded broke off the Ross ice shelf and was about the size of Jamaica at 11,000 square kms.

Bits have lingered for years.

The loss of ice shelves does not in itself affect sea levels because the ice is already floating.

But their disappearance lets glaciers on land slip faster towards the ocean, thereby raising sea levels.

NASA estimates that the Larsen C ice shelf pins back ice on land that would add a centimeter (0.4 inches) to world sea levels, which have gained about 20 centimeters in the past century.

(Reporting By Alister Doyle; Editing by Gareth Jones)

(c) Copyright Thomson Reuters 2017. Posted Image

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Antarctic iceberg: Giant 'white wanderer' poised to break free

Jonathan Amos
Science correspondent

5 July 2017

Everybody is fascinated by icebergs.

The idea that you can have blocks of frozen water the size of cities, and bigger, sparks our sense of wonder.

British astronaut Tim Peake photographed one from orbit that would just about fit inside Central London's ring road.

But at 26km by 13km (16 miles by 8 miles), it was a tiddler compared with the berg that is about to break away from the eastern side of the Antarctic Peninsula.

A rift has grown across the edge of the Larsen C Ice Shelf.

A thin, 5km-long section of the floating shelf is now all that prevents a 6,000-sq-km berg from drifting away into the Weddell Sea.

Think about the size for a moment.

That's more than a quarter the area of Wales.

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A big berg, certainly, but the largest in the satellite era was almost double this size

Keen to gather some more statistics, scientists have used the Cryosat spacecraft to run the rule over the putative iceberg.

As we all know, blocks of ice sit mostly under the water, and the European Space Agency (Esa) satellite has a special radar altimeter that is able to figure out by how much.

From orbit, Cryosat senses the height of the ice sticking above the surface - the so-called freeboard. It's then a relatively simple calculation to work out the draft - the hidden part below water.

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An icy colossus: Big bergs need to be tracked because they can eventually reach shipping lanes

"Cryosat has these two radar antennas that allow us to get an extensive swath across the berg and enable us to build an elevation model," Dr Noel Gourmelen from the University of Edinburgh told BBC News.

From this, the average thickness of the would-be berg is calculated to be about 190m, but there are places where the draft is around 210m.

It means the ice above the water surface stands roughly 30m high.

Dr Gourmelen says there is an estimated 1,155 cubic km of ice in the block.

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The drift paths (red lines) of countless bergs have been tracked around the Antarctic continent (black). This collective history strongly suggests the Larsen block will head for the South Atlantic

This is all very useful information because it tells scientists a lot about where and how fast the Larsen object might move once it becomes free.

And those are critical details if the berg were to reach shipping lanes to become a navigation hazard.

Bergs are influenced by winds and currents, of course, but a couple of other factors also come in to play simply because of the Larsen object's sheer bulk.

Remarkably, one is a gravitational effect.

The mass of Antarctica pulls the water higher near its coasts compared with the centre of the ocean - by something like half a metre.

The Larsen berg will actually slide down this slope.

But that's only if its keel doesn’t then snag on the ocean bottom.

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Ploughmarks: The keels of icebergs will cut deep channels in sea-floor sediments

The waters close to Antarctica are shallow and there's a good chance the berg will dig in, gouging a huge trough in the seafloor as it then turns round.

Cryosat's thickness information tells researchers where the berg can and cannot go.

It's called "kedging" - a term used by sailors, coined from the use of the kedge anchor to manipulate the course of a vessel, explains Dr Mark Drinkwater, one of Esa's senior Earth observation scientists.

“The icebergs often shoal and pivot or spin around their grounding point, resulting in stop and go motion or a change in direction. So, the iceberg from Larsen C could take some time before it escapes the shallow [waters] of the western Weddell Sea."

Dr Anna Hogg from Leeds University added: "That said, it's not impossible it could simply become stuck on some high-rise topography on the ocean floor. We've seen that before where an iceberg becomes a semi-permanent ice island in the Weddell Sea."

The expectation, however, is that the berg will bump and grind its way northward in near-coast currents, along the Peninsula.

Posted Image

Past history suggests it will eventually be exported on one of four major iceberg "highways" that lead beyond Antarctica.

In this instance, the route is one that sends the berg into the circumpolar current and on to an eastward arc towards the South Atlantic.

The penguins and seals on the British Overseas Territory of South Georgia may well get to see it, or its fragments, as it passes by in a few years' time.

And I mean years.

Prof Helen Fricker, from California's Scripps Institution of Oceanography, says she was tracking two large objects in 1993, a full seven years after their 95km-by-95km parent berg calved from the Larsen C Ice Shelf.

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Tim Peake's iceberg, known as A-56, was roughly 26km by 13km (16 miles by 8 miles)

What's nice about Tim's berg is that he managed to capture it on a normal SLR optical camera.

That's unusual because Antarctica is very often covered in cloud, and it doesn't matter how big a lens you have - the ocean surface will be obscured.

It's why radar satellites are so important.

The wavelengths they work at pierce cloud and winter darkness.

Indeed, the only reason we know this new Larsen berg is about to calve is because Europe's Sentinel-1 radar satellites take a detailed look at the shelf's behaviour every six days.

"What the current Larsen situation has highlighted is that we're now able to monitor the situation with a frequency we've never had before," says Dr Hogg.

"We can get pictures from the two Sentinel-1 satellites in about half an hour of them being acquired. The satellites we have now are revolutionising our study of the polar regions," she told BBC News.

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How are Antarctic icebergs named?

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Iceberg names follow a convention that uses a letter followed by a number

- Icebergs are blocks of ice that cover at least 500 sq m

- Any smaller and they are called "growlers" or "bergy bits"

- The US National Ice Center runs the naming system for bergs

- It divides Antarctica into quadrants - A, B, C and D

- Larsen icebergs get an "A" designation when they calve

- They also get the next number in the sequence of sightings

____________________________________________________________________________________________________________________________________________

Source: Posted Image .com
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Trillion Tonne Iceberg Breaks Off Antarctica

July 12, 2017 by Reuters

By Nina Chestney LONDON, July 12 (Reuters) – One of the biggest icebergs on record has broken away from Antarctica, scientists said on Wednesday, creating an extra hazard for ships around the continent as it breaks up.

The one trillion tonne iceberg, measuring 5,800 square km, calved away from the Larsen C Ice Shelf in Antarctica sometime between July 10 and 12, said scientists at the University of Swansea and the British Antarctic Survey.

The iceberg, which is roughly the size of the U.S. state of Deleware or the Indonesian island of Bali, has been close to breaking off for a few months.

Throughout the Antarctic winter, scientists monitored the progress of the rift in the ice shelf using the European Space Agency satellites.

“The iceberg is one of the largest recorded and its future progress is difficult to predict,” said Adrian Luckman, professor at Swansea University and lead investigator of Project MIDAS, which has been monitoring the ice shelf for years.

“It may remain in one piece but is more likely to break into fragments. Some of the ice may remain in the area for decades, while parts of the iceberg may drift north into warmer waters,” he added.

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Source: University of Swansea

The ice will add to risks for ships now it has broken off.

The peninsula is outside major trade routes but the main destination for cruise ships visiting from South America.

In 2009, more than 150 passengers and crew were evacuated after the MTV Explorer sank after striking an iceberg off the Antarctic peninsula.

The iceberg, which is likely to be named A68, was already floating before it broke away so there is no immediate impact on sea levels, but the calving has left the Larsen C ice shelf reduced in area by more than 12 percent.

The Larsen A and B ice shelves, which were situated further north on the Antarctic Peninsula, collapsed in 1995 and 2002, respectively.

“This resulted in the dramatic acceleration of the glaciers behind them, with larger volumes of ice entering the ocean and contributing to sea-level rise,” said David Vaughan, glaciologist and director of science at British Antarctic Survey.

“If Larsen C now starts to retreat significantly and eventually collapses, then we will see another contribution to sea level rise,” he added.

Big icebergs break off Antarctica naturally, meaning scientists are not linking the rift to manmade climate change.

The ice, however, is a part of the Antarctic peninsula that has warmed fast in recent decades.

“In the ensuing months and years, the ice shelf could either gradually regrow, or may suffer further calving events which may eventually lead to collapse – opinions in the scientific community are divided,” Luckman said.

“Our models say it will be less stable, but any future collapse remains years or decades away.”

(c) Copyright Thomson Reuters 2017. Posted Image

Source: Posted ImagegCaptain.com
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Giant iceberg splits from Antarctic

By Jonathan Amos
BBC Science Correspondent

12 July 2017

Posted Image
This view of the iceberg was taken by Nasa's Suomi NPP satellite

One of the biggest icebergs ever recorded has just broken away from Antarctica.

The giant block is estimated to cover an area of roughly 6,000 sq km; that's about a quarter the size of Wales.


A US satellite observed the berg on Wednesday while passing over a region known as the Larsen C Ice Shelf.

Scientists were expecting it.

They'd been following the development of a large crack in Larsen's ice for more than a decade.

The rift's propagation had accelerated since 2014, making an imminent calving ever more likely.

The more than 200m-thick tabular berg will not move very far, very fast in the short term.

But it will need to be monitored.

Currents and winds might eventually push it north of the Antarctic where it could become a hazard to shipping.

An infrared sensor on the American space agency's Aqua satellite spied clear water in the rift between the shelf and the berg on Wednesday.

The water is warmer relative to the surrounding ice and air - both of which are sub-zero.

"The rift was barely visible in these data in recent weeks, but the signature is so clear now that it must have opened considerably along its whole length," explained Prof Adrian Luckman, whose Project Midas at Swansea University has followed the berg's evolution most closely.

The event was confirmed by other spacecraft such as Europe's Sentinel-1 satellite-radar system.

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Europe's Sentinel-1 satellite-radar system confirmed the calving event

How does it compare with past bergs?

The new Larsen berg is probably in the top 10 biggest ever recorded.

The largest observed in the satellite era was an object called B-15.

It came away from the Ross Ice Shelf in 2000 and measured some 11,000 sq km.

Six years later, fragments of this super-berg still persisted and passed by New Zealand.

In 1956, it was reported that a US Navy icebreaker had encountered an object of roughly 32,000 sq km.

That is bigger than Belgium.

Unfortunately, there were no satellites at the time to follow up and verify the observation.

It has been known also for the Larsen C Ice Shelf itself to spawn bigger bergs.

An object measuring some 9,000 sq km came away in 1986.

Many of Larsen's progeny can get wound up in a gyre in the Weddell sea or can be despatched north on currents into the Southern Ocean, and even into the South Atlantic.

A good number of bergs from this sector can end up being caught on the shallow continental shelf around the British overseas territory of South Georgia where they gradually wither away.

What is the significance of the calving?

In and of itself, probably very little.

The Larsen C shelf is a mass of floating ice formed by glaciers that have flowed down off the eastern side of the Antarctic Peninsula into the ocean.

On entering the water, their buoyant fronts lift up and join together to make a single protrusion.

The calving of bergs at the forward edge of the shelf is a very natural behaviour.

The shelf likes to maintain an equilibrium and the ejection of bergs is one way it balances the accumulation of mass from snowfall and the input of more ice from the feeding glaciers on land.

That said, scientists think Larsen C is now at its smallest extent since the end of the last ice age some 11,700 years ago, and about 10 other shelves further to the north along the Peninsula have either collapsed or greatly retreated in recent decades.

The two nearby, smaller shelves, Larsen A and Larsen B, disintegrated around the turn of the century; and a warming climate very probably had a role in their demise.

But Larsen C today does not look like its siblings.

Prof Helen Fricker, from the Scripps Institution of Oceanography, told BBC News: "The signs we saw at Larsen A and B - we're not seeing yet. The thinning we saw for Larsen A and B - we're not seeing. And we're not seeing any evidence for large volumes of surface meltwater on the order of what you would need to hydro-fracture the ice shelf.

"Most glaciologists are not particularly alarmed by what's going on at Larsen C, yet. It's business as usual."

Posted Image

Researchers will be looking to see how the shelf responds in the coming years, to see how well it maintains a stable configuration, and if its calving rate changes.

There was some keen interest a while back when the crack, which spread across the shelf from a pinning point known as the Gipps Ice Rise, looked as though it might sweep around behind another such anchor called the Bawden Ice Rise.

Had that happened, it could have prompted a significant speed-up in the shelf's seaward movement once the berg came off.

As it is, scientists are not now expecting a big change in the speed of the ice.

One fascinating focus for future study will be a strip of "warm", malleable ice that runs east-west through the shelf, reaching the ocean edge about 100km north from the Gipps Ice Rise.

This strip is referred to as the Joerg suture zone.

There is a large queue of cracks held behind it.

"Calving of the iceberg is not likely itself to make the existing cracks at the Joerg Peninsula suture zone more likely to jump across this boundary," observed Chris Borstad, from the University Centre in Svalbard (UNIS).

"At this stage we really don't know whether there is some larger-scale process that might be weakening this zone, like ocean melting at the base of the shelf, or whether the current rift was just a random or episodic event that was bound to happen at some point.

"We know that rifts like this periodically propagate and cause large tabular icebergs to break from ice shelves, even in the absence of any climate-driven changes.

"I am working with a number of colleagues to design field experiments on Larsen C to answer this specific question (by measuring the properties of the Joerg suture zone directly). But until we get down there and take some more measurements we can only speculate."

Posted Image
Scientists want to understand why a lot of cracks seem not to propagate across the ice shelf

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Drifting Antarctic iceberg A-68 opens up clear water

By Jonathan Amos
BBC Science Correspondent

6 hours ago

Posted Image

The giant iceberg known as A-68 that was produced in the Antarctic last week continues to drift seaward.

All the latest satellite images indicate the gap between the 6,000-sq-km block and the floating Larsen C Ice Shelf from which it calved is widening.

The particular image on this page was acquired by the Deimos-1 satellite.

It is not easy getting pictures of the Antarctic at this time of year because of the long winter nights and because of cloud cover.

Those spacecraft that have so far spied the berg have been relying on radar or on infrared sensors to pierce these difficulties.

The monster berg - which is a quarter the size of Wales, and one of the biggest ever recorded - is so far behaving as expected.

Theory suggests it should move, in the first instance, down the slope in the ocean surface that has been created by winds in the Weddell Sea pushing water up against the coast.

But the leftward deflecting effect of the Coriolis force, produced by the Earth's rotation, should keep the berg relatively close to the continent's edge.

Interestingly in the Deimos image, acquired on Friday, it appears as though a large segment of "fast ice" that was attached to the berg has broken free.

This fast ice is considerably thinner than the main block - a few metres thick versus the 200-plus-metres of the berg itself.

Posted Image
In this Sunday thermal image from Nasa's Aqua satellite, the strong white lines are the signal of water which is warm relative to the surrounding ice and air. It also suggests a large section of fast ice has detached from the berg

Thomas Rackow and colleagues from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, are following the block with keen interest.

They recently published research in which they modelled the drift of icebergs through Antarctic waters - taking into account the different influences that act on small and large objects.

There are essentially four "highways" that bergs travel, depending on their point of origin.

A-68 should follow the highway up the eastern coast of the Antarctic Peninsula, leading from the Weddell Sea towards the Atlantic.

"It will most likely follow a northeasterly course, heading roughly for South Georgia and the South Sandwich Islands," Dr Rackow told BBC News. "It will be very interesting to see whether the iceberg will move as expected, as a kind of 'reality-check' for the current models and our physical understanding."

Posted Image
Simulated highways: Small to medium bergs (Classes 1-3) generally have a lifetime of a couple of years; the big bergs (Classes 4-5) are mostly all gone after 10 years

Polar research agencies are already discussing the scientific opportunities afforded by the breakaway.

Scientists will want to understand what effect the calving might have on the remaining parts of the ice shelf.

Ten percent of Larsen C's area was removed by the departing berg, and this loss could change the way stress is configured and managed across the shelf.

There are numerous cracks just north of a pinning point known as the Gipps Ice Rise.

These fissures have long remained static, held in place by a band of soft, malleable ice.

Researchers will want to check the departure of A-68 will not alter the status of these cracks.

There are also some fascinating investigations to be done on the seafloor that will soon be uncovered when the berg moves completely clear of the shelf.

Previous big calvings have led to the discovery of new species.

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British mission to giant A-68 berg approved

By Jonathan Amos
BBC Science Correspondent

9 hours ago

Posted Image
A large gap is opening between the berg and the Larsen Ice Shelf (image from 2 October)

UK scientists will lead an international expedition to the huge new iceberg that recently calved in the Antarctic.

A-68, which covers an area of almost 6,000 sq km, broke away in July.

Researchers are keen to investigate the seafloor uncovered by the trillion-tonne block of ice.

Previous such ventures have discovered new species.

The British Antarctic Survey has won funding to visit the berg and its calving zone in February next year.

It will use the Royal Research Ship James Clark Ross.

Posted Image

BAS cautions, however, that the final green-light will depend on the berg's position at the time and the state of sea-ice in the area.

A-68 will need to be well clear of the Larsen Ice Shelf from which it calved, and any marine floes on top of the water will have to be sufficiently thin to allow the JCR access.

"It's fantastic news to have won approval," BAS marine biologist Dr Katrin Linse, who will lead the cruise, told BBC News.

"Antarctic vessels are normally booked out years in advance and for our funders, Nerc, to give us the opportunity on this urgency grant to go this coming season is brilliant."

The drifting berg, one of the biggest ever recorded in the Antarctic, is exposing seafloor that probably has not been free of ice cover for 120,000 years - during the peak of the last warm phase in Earth's history known as the Eemian.

The area has already gained protected status from the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).

This gives scientists priority access and keeps commercial fishing at bay for a minimum of two years, but in all likelihood 10 years.

"We don't really know what we'll find; that's what's so exciting," says Dr Linse. "This unknown biodiversity has been covered by shelf ice for thousands of years. It's had no sunlight and therefore it has had no food coming in through phytoplankton."

Past experience, though, tells the scientists they should encounter animals similar to those seen in the Antarctic deep sea - organisms that also live far away from sunlight many hundreds, even thousands, of metres down.

These include particular types of sea cucumber, starfish, bivalves and sponges, some of which have become carnivores in the absence of a phytoplankton food supply.

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Luckily, the JCR was already scheduled to be in the region

The research cruise will take samples through the water column and from the bottom sediments.

The intention is to establish a baseline from which to assess future change, as organisms that would not normally live under ice start to move in.

These "pioneers", such as large glass sponges, are expected to have begun their colonisation by the time the German research ship Polarstern visits the area in February/March 2019.

This cruise is led from the Alfred Wegener Institute in Bremerhaven but its members will also be on the JCR and vice versa.

Posted Image
The Sentinel 3 satellite obtained this view through the cloud on Sunday, 1 October

At present, satellite images are used to monitor the berg's position, but with the region now emerging from the austral winter it is only a matter of time before an aircraft is sent to film the ice block.

BAS intends to do this in early 2018.

"We'll pass the berg in the JCR, certainly, but we can't take samples off it because you never know how stable the sides are going to be," Dr Linse added.

"We'd like to get some footage from the air and will have some drones onboard to do that."

A-68 has been calculated to have an average thickness of about 190m, but there are places where the draft is around 210m.

This means there will be some ice walls standing above the water line that may be roughly 30m high.

Source: Posted Image.com
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UK's Halley Antarctic base set for second closure

By Jonathan Amos
BBC Science Correspondent

31 October 2017

Posted Image
Scientists had been keen to return to year-round operations

The British Antarctic Survey (BAS) will once again close its Halley station at the end of the coming Southern Hemisphere summer.

The base sits on the floating Brunt Ice Shelf, which is currently being incised by two large developing cracks.

BAS withdrew its staff from Halley this past winter because of uncertainty over how these fissures would evolve.

The survey has now confirmed it will do the same again when the approaching summer season comes to an end.

"What we are witnessing is the power and unpredictability of nature," said BAS director Prof Dame Jane Francis.

"The safety of our staff is our priority in these circumstances. Our Antarctic summer research operation will continue as planned, and we are confident of mounting a fast uplift of personnel should fracturing of the ice shelf occur.

"However, because access to the station by ship or aircraft is extremely difficult during the winter months of 24-hour darkness, extremely low temperatures and the frozen sea, we will once again take the precaution of shutting down the station before the 2018 Antarctic winter (March - November) begins."

BAS staff will fly into Halley this week to open it up.

One of their key tasks in the next few months will be to install automated experiments that can run in winter temperatures of -50C, and cope with snow and high winds.

The UK has had a permanent presence on the Brunt Ice Shelf since 1956.

Together with the Rothera base on the Antarctic Peninsula, Halley spearheads British activity on the White Continent.

The station gathers important weather and climate data, and it played a critical role in the research that identified the ozone "hole" in 1985.

In recent years, Halley has also become a major centre for studying solar activity and the impacts this can have on Earth.

But its position on a 150m-thick mobile platform of ice has always had a bearing on its operations.

In the past, as the shelf has moved seaward to calve icebergs, the buildings that make up the base have either been abandoned or torn down.

New structures have then been built "upstream".

The latest incarnation of the station, Halley VI, is somewhat different in that it incorporates legs and skis that allow it periodically to be towed to a new location.

Its first big move took place in February, to get the base behind a large chasm that had started opening again after more than 30 years of dormancy.

But it was a timely decision because another crack (known as Halloween crack) had also begun moving across the ice.

And both fissures, which threaten at some point to spawn colossal icebergs, have continued to propagate through the winter.

Posted Image
Scientists use ground sensors and satellites to monitor the cracks

In a report published this month in the journal The Cryosphere, BAS scientists said the future behaviour of the Brunt shelf now depended on how the two cracks interacted with a series of bumps on the seafloor known as the McDonald rumples.

These are a pinning point for the shelf and act to buttress it.

If calving results in a substantial loss of ice around the rumples then the whole shelf will speed up.

A similar event in the early 1970s led to a two-fold increase in flow velocity.

The early operations team going into Halley this week will be followed by a larger group of staff on the Royal Research Ship Ernest Shackleton, which will come in from Cape Town and moor up against the ice shelf to unload supplies.

BAS director of science Prof David Vaughan said researchers had already planned for the possibility of another winter closure, and would set up a kerosene-fuelled generator to power automated instruments.

"It is, I should stress, at this stage just a prototype power system," he told BBC News.

"For it to keep running at -50C with nobody around to chip the ice off it or keep the snow away from it will be a significant challenge.

"But if it works and the instruments attached to it keep working, then we will collect several of the data streams that would otherwise have been lost, including the ozone measurements."

Source: Posted Image.com
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Antarctic base comes out of deep freeze

By Jonathan Amos
BBC Science Correspondent

10 November 2017

Posted Image
In good shape: Halley station is now being readied for the summer season

The advance party sent in to open up Britain’s mothballed Antarctic base have found no damage.

Halley station was closed in March and staff withdrawn because of uncertainty over the behaviour of cracks in the Brunt Ice Shelf - the flowing, floating platform on which it sits.

The base was secured and left to the elements, with temperatures dipping down to around -50C.

But the first arrivals say Halley is none the worse for its shut-down.

The British Antarctic Survey (BAS) flew a party of 12 into the base to start switching all the utilities back on - the power and heating.

One fear was that windows might have broken in a storm and that this could have allowed snow to get inside.

But that has not been the case.

Halley operations manager John Eager said: "The team was very pleased to find the station in such good shape. It's testament to how well last season's team carried out the shut-down just after we successfully re-located the modules 23km inland.

"Apart from a few carpet tiles lifting, and some crazing on inner glazing, everything is exactly as we left it. It is early days in the season, and many complex challenges remain, but it's a great start by the team on the ice."

Some further technical investigations are being carried out to assess how well all the materials and equipment faired during winter.

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Halley should be occupied year-round

Halley is now being prepared for the annual southern summer influx of scientists in the coming weeks.

The Royal Research Ship Ernest Shackleton is also expected soon with supplies.

Together with the Rothera base on the Antarctic Peninsula, Halley spearheads British activity on the White Continent.

The station gathers important weather and climate data, and it played a critical role in the research that identified the ozone "hole" in 1985.

In recent years, Halley has also become a major centre for studying solar activity and the impacts this can have on Earth.

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Some detailed technical investigations continue at Halley

Halley is supposed to be a year-round station, but its position on the 150m-thick Brunt Ice Shelf has always had a bearing on its operations.

Two fissures are spreading across the shelf. One is a large chasm cutting in front of the base on its seaward side, the other is a long, arcing split that is moving eastwards and away from Halley.

Both fissures are set to spawn big icebergs.

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Halley's library: The facilities will soon be in use by scientists

The concern for glaciologists is that both cracks run near to a feature known as the McDonald Ice Rumples.

This is a raised area of seafloor that helps pin the shelf in place.

“We hope - as we actually predict - that the chasm will not disconnect the shelf from the rumples. But it is a concern that if that were to happen we don’t know what the stability of the shelf will be in the long term,” BAS science director Prof David Vaughan told BBC News.

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The summer accommodation blocks and garages

It is this uncertainty that has prompted BAS to make Halley a summer-only base for the time being.

Evacuation is relatively straightforward in the benign months around the turn of the year, but it becomes extremely hazardous when winter weather is coupled with long polar nights (105 days are spent in 24-hour darkness).

En route now to Halley is a so-called micro-turbine - a kind of “jet engine in a box”.

This will be used to power automated instruments next winter when the base is once again in shut-down.

The turbine is designed to run for thousands of hours without servicing and should provide sufficient electricity to warm the experiments.

Scientists are keen to maintain a basic stream from Halley of weather data, ozone readings, and geomagnetic observations.

Source: Posted Image.com
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UK team set for giant Antarctic iceberg expedition

By Victoria Gill
Science correspondent, BBC News

12 February 2018

Scientists will set out in the next week to study an Antarctic realm that has been hidden for thousands of years.

A British Antarctic Survey-led team will explore the seabed ecosystem exposed when a giant iceberg broke away from the Antarctic Peninsula in 2017.

The organisation has also released the first video of the berg, which covers almost 6,000 sq km.

Its true scale begins to emerge in a shot filmed from an aircraft flown along its edge.

Urgent mission

An international team will spend three weeks, from February to March, on board the research ship RRS James Clark Ross, navigating ice-infested waters to reach the remote Larsen C ice shelf from which the berg calved.

Posted Image
A large gap between the berg and the Larsen Ice Shelf is increasing in size

British Antarctic Survey marine biologist Dr Katrin Linse, who is leading the mission, said that the calving of the iceberg, which has been named A68, provides researchers with "a unique opportunity to study marine life as it responds to a dramatic environmental change".

"It's important we get there quickly before the undersea environment changes as sunlight enters the water and new species begin to colonise," she explained, adding that the mission was "very exciting".

Prof David Vaughan, science director at BAS stressed that it was a treacherous journey but said the team needed to "be bold".

"Larsen C is a long way south and there's lots of sea ice in the area, but this is important science, so we will try our best to get the team where they need to be," he said.

"The calving of A68 offers a new and unprecedented opportunity to establish an interdisciplinary scientific research programme in this climate-sensitive region. Now is the time to address fundamental questions about the sustainability of polar continental shelves under climate change."

Source: Posted Image.com
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Mission to giant A-68 berg thwarted by sea-ice

By Jonathan Amos
BBC Science Correspondent

2 March 2018

Scientists have had to abandon their plan to investigate the waters around the world's biggest iceberg.

The team, led by the British Antarctic Survey, was thwarted in its attempts to reach the massive block known as A-68 by thick sea-ice in the Weddell Sea.

The iceberg broke away from the Larsen C Ice Shelf on the eastern side of the Antarctic Peninsula last July.

It revealed portions of the sea-floor that had been covered for many thousands of years.

The team, which is on the Royal Research Ship James Clark Ross, had been hoping to sample what were likely to be new species.

These animals would have had to adapt to an environment devoid of light to survive.

Posted Image

"We knew that getting through the sea-ice to reach Larsen C would be difficult," said expedition leader Dr Katrin Linse.

"Naturally, we are disappointed not to get there but safety must come first.

"The captain and crew have been fantastic and pulled out all the stops to get us to the ice shelf, but our progress became too slow, with just 8km travelled in 24 hours and we still had over 400km to travel. Mother Nature has not been kind to us on our mission.

"But we have a 'Plan B'; we will head north to areas which have never been sampled for benthic biodiversity.

"The Prince Gustav Channel Ice Shelf and neighbouring Larsen A Ice Shelf collapsed in 1995. We'll be sampling deeper than we planned at Larsen C - down to 1,000m - so we're excited about what deep sea creatures we might find."

Posted Image
A-68 is so big its scale is impossible to convey in a single photo

The expedition has gone later in the Antarctic season than it would have been ideal, but the urgent proposal to go sample A-68's waters had to fit with BAS schedules that had long been agreed for this season.

Normally, it takes a few years to put such a venture together.

There should, however, still be an opportunity to visit the berg next year as many on the current expedition will join a German effort run out of the Alfred Wegener Institute.

It will use the Research Vessel Polarstern.

In the meantime, the BAS Plan B goes into action.

It will see the team collect seafloor animals, microbes, plankton, sediments and water samples in the vicinity of the alternative ice shelves.

Source: Posted Image.com
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The 'monster' iceberg: What happened next?

Jonathan Amos
Science correspondent

9 July 2018

It was a wow! moment.

The world's biggest berg, a block of ice a quarter the size of Wales, fell off the Antarctic exactly a year ago.

But what then?

We've gone back to find out.

Weighing a trillion tonnes and covering an area of nearly 6,000 sq km, the colossus dubbed A-68 has kind of spent the past 12 months shuffling on the spot - rather like grandpa trying to get himself out of a tight parking spot at the supermarket.

Occasionally, the berg head-butted the floating shelf of ice from which it calved, but made only limited progress in moving north - its expected path out of the Antarctic's Weddell Sea towards the Atlantic Ocean.

"An iceberg as massive as A-68 is sluggish, and thus needs time to accelerate," explains Thomas Rackow from Germany's Alfred Wegener Institute.

"Compared to much smaller icebergs, A-68 is also less sensitive to offshore winds that could potentially drive the iceberg away from the continent. In fact, since the calving event in early July last year, we could see the iceberg going back and forth due to the prevailing winds."

Dr Rackow says the frozen ocean surface probably also played some role in constraining the berg's movement, and wonders if the underside of the berg was catching on the seafloor.

It's a thought shared by Suzanne Bevan at Swansea University, UK.

"We know so little about the bathymetry (depth) in that area of the Weddell Sea," she told BBC News.

Given time, though, A-68 should pick up the pace as the currents grab hold of it.


And A-68 hasn't melted?

Nope.

It's extremely cold in that part of the world.

The berg has knocked off some of its sharp edges, but it remains much as it was - 150km long and 55km wide.

Two largish chunks have detached, one of them sufficiently big to get its own designation (A-68b) in the list of giant bergs kept by the US National Ice Center.

The American agency has officially now put A-68 at number six in its all-time ranking.

If you were wondering - a berg called B15 is the historic champ.

It was roughly 11,000 sq km in area when it broke away from Antarctica back in 2000.

And it's still going, albeit in pieces.

Astronauts on the space station recently photographed the largest remaining fragment of B15 passing the British Overseas Territory of South Georgia on its way to the equator.

A-68 will very probably travel this same "iceberg alley".

Posted Image
Eighteen years on, B-15 is now a shadow of its former self


What's A-68 like if you go there?

Ella Gilbert from the British Antarctic Survey was the first to make a movie of the berg from close quarters.

The scientist was in a small plane gathering atmospheric data when she made a low pass along its edge.

"It took us an hour and a half to go from one side to the other," she says. "It's scale is mind-boggling, fascinating - it's like another world. It was possibly the most exciting thing I've ever done."

Ella is often asked why the berg broke away.

"It's complicated," she explains. "The region is clearly undergoing a lot of change but you can't just say 'it was the climate'. Iceberg calving is a natural process anyway. If you put more snow in at one end, it has to come out the other end as icebergs."

Posted Image
Ultimately, it's expected A-68 will enter "iceberg alley" into the Atlantic


So, why should we be interested?

A-68 broke away from the Larsen C Ice Shelf - the floating extension of glaciers running off the Antarctic Peninsula.

The shelf is the subject of intense scrutiny because similar structures to the north have disintegrated.

Climate warming very probably was implicated in some of these losses, and so it is inevitable that people will ask what the future holds for Larsen C.

It is one of the biggest ice shelves in all of Antarctica and its collapse would allow its feeding glaciers to dump more of their ice into the ocean, raising sea-levels.

Posted Image


How likely is that to happen?

The answer to this question will only come with ongoing monitoring.

The first thing scientists want to understand is how the shelf will react to calving such a big berg.

The stresses acting on the shelf will almost certainly have changed.

"The models tell us we should expect the centre of the Larsen C Ice Shelf to speed up a bit, and the edges, where the berg was attached, to slow down," says Swansea's Adrian Luckman, whose Midas research group was most closely involved in monitoring A-68's break-away.

But this behaviour is very difficult to demonstrate because tidal movements push on the shelf and complicate the satellite measurements.

Posted Image
A-68 should pick up the pace as the currents grab hold of it


Tell me about a surprising discovery

Scientists have established that the surface of the Larsen C Ice Shelf can melt even during the deep freeze of permanent night in the Antarctic winter.

Weather station and satellite observations have established that a particular type of warm westerly wind, or Foehn, will flow down off the peninsula mountains to produce ponds on the surface of the shelf.

"You see this in May, which in the Antarctic is equivalent to late November. Forty percent of the melt in 2016 occurred in this winter period - all because of the Foehn effect," says Adrian Luckman.

This is a process scientists will need to watch closely.

Some of those northern shelves that collapsed were destabilised by the presence of large numbers of meltwater lakes on their surface.

Larsen C is far from replicating such conditions but that may change in the coming decades if global warming progresses as expected and its effects impinge deeper into the Antarctic.

Posted Image
Image copyrightESA

Posted Image
The drift paths (red lines) of countless bergs have been tracked around the Antarctic continent (black). This collective history strongly suggests A-68 will head for the South Atlantic

Source: Posted Image bbc.com
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