The Antarctic Half of the Global Thermohaline Circulation is Collapsing
Exploring Hydrocarbon Depletion
The Antarctic Half of the Global Thermohaline Circulation is Collapsing
onlooker wrote:http://m.dailykos.com/story/2014/03/05/1281907/-The-Antarctic-Half-of-the-Global-Thermohaline-Circulation-is-Collapsing?detail=facebookThe Antarctic Half of the Global Thermohaline Circulation is Collapsing
An iceberg expected to be one of the 10 largest ever recorded is ready to break away from Antarctica, scientists say.
A long-running rift in the Larson C ice shelf grew suddenly in December and now just 20km of ice is keeping the 5,000 sq km piece from floating away.
Larsen C is the most northern major ice shelf in Antarctica. Larsen C is about 350m thick and floats on the seas at the edge of West Antarctica, holding back the flow of glaciers that feed into it.
Researchers based in Swansea say the loss of a piece a quarter of the size of Wales will leave the whole shelf vulnerable to future break-up.
Last year, researchers from the UK's Project Midas reported that the Larsen C rift was growing fast.
But in December the speed of the rift went into overdrive, growing by a further 18km in just a couple of weeks. What will become a massive iceberg now hangs on to the shelf by a thread just 20km long.
However, they are concerned about how any break-off will impact the rest of the ice shelf, given that its neighbour, Larsen B, disintegrated spectacularly in 2002 following a similar large calving event.
A chunk of ice half the size of Jamaica which is breaking away from West Antarctica is now attached to its parent ice shelf just by a thread, scientists reported Friday.
The rift in the Larsen C Ice Shelf has grown a further 10km since 1 January.
If the fissure propagates just 20km (12 miles) 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 (1600 ft)-thick floating ice shelf on the eastern side of the Antarctic Peninsula comes from the EU’s Sentinel-1 satellite system.
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.
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.
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.
An iceberg the size of Delaware is poised to break away from Antarctica, an event which may lead to the collapse of a massive ice shelf on the continent, according to researchers.
Scientists say that a 1,900 square-mile section of the "Larsen C" ice shelf is now only connected to the main body by a 12-mile section of ice. Researchers monitoring a huge crack in the ice discovered that it had grown rapidly during the second half of 2016 — increasing in size by 11 miles in December alone.
Scientists have been monitoring the rift on the ice shelf for decades. Researchers told NBC News that the calving event was "part of the natural evolution of the ice shelf," but added there could be a link to changing climate, though they had no direct evidence of it.
In response to expressions of concern on social media, MIDAS scientists responded that there was no need for alarm. "This is a fairly normal event, although it is spectacular and quite rare
The Larsen Ice Shelf lies in and among: twenty-six semi-active (non-erupting but heat-flowing) land volcanoes, four actively erupting land volcanoes, two proven semi-active seafloor volcano (seamounts), and a proven actively heat flowing major fault system named the West Antarctic Rift.
Not shown on this map are known seafloor hydro-thermal vents (hot seafloor geysers), likely heat emitting fractures, and prominent cone-shaped seafloor mountains that are most likely seamounts (ocean volcanoes).
This geological information paints a very clear and compelling picture that the Larsen Ice Shelf is positioned in an extremely active geological setting. In fact a strong case can be made that the Larsen Ice Shelf owes its very existence to a down-faulted low valley that has acted as a glacial ice container
The Larsen C rift was first noticed by MIDAS researchers in 2014, and has been monitored by satellites and other instruments ever since. In November 2016, NASA's IceBridge mission observed the immense crack, which then measured 70 miles (112 km) long, 300 feet (91 meters) wide and about one-third of a mile (0.5 km) deep.
Given the rate at which the rift is growing, the iceberg could break away early this year, MIDAS researcher Adrian Luckman, a professor of glaciology at Swansea University in the United Kingdom, 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," Luckman told BBC News. "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."
17 February 2017 • 12:38am
Glacial 'aftershock' spawns Antarctic iceberg the size of Manhattan
Antarctica's rapidly melting Pine Island Glacier has shed an iceberg the size of Manhattan, the latest evidence of the ice shelf’s fragility.
Nasa released photographs showing the block of ice separating from the southwest coast of the continent taken between January 26 and January 31.
The sequence, taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) on Nasa’s Terra satellite, shows the berg when it first broke and then as it drifts in the bay.
According to Ian Howat, a glaciologist at Ohio State University, the event was about 10 times smaller than in July 2015, when a 30-kilometre-long (20-mile) rift developed below the ice surface, then broke through and calved an iceberg spanning 583 square kilometers (225 square miles).
“I think this event is the calving equivalent of an ‘aftershock’ following the much bigger event,” Mr Howat said. “Apparently, there are weaknesses in the ice shelf - just inland of the rift that caused the 2015 calving - that are resulting in these smaller breaks.”
Scientists have observed other small rifts in the glacier which are predicted to bring more calving in the near future.
“Such ‘rapid fire’ calving does appear to be unusual for this glacier,” Mr Howat said. But the phenomenon “fits into the larger picture of basal crevasses in the centre of the ice shelf being eroded by warm ocean water, causing the ice shelf to break from the inside out.”
Scientists have been closely monitoring Pine Island, one of the main glaciers responsible for moving ice from the interior of the West Antarctic Ice Sheet to the ocean, and its connection to rising sea levels.
They have observed an increase in the speed of the loss of ice which ultimately would contribute to sea level rise.
The Amundsen Sea sector of the West Antarctic Ice Sheet has most likely been destabilized and ice retreat is unstoppable for the current conditions.
No further acceleration in climate change is necessary to trigger the collapse of the rest of the West Antarctic Ice Sheet, with loss of a significant fraction on a decadal to century time scale.
Antarctica has the potential to contribute more than a metre of sea-level rise by 2100.
A large fraction of West Antarctic basin ice could be gone within two centuries, causing a 3–5 metre sea level rise.
”...once you get off of the stabilizing sill, whenever that is in West Antarctica, the time scale of getting rid of the West Antarctic [3.3m GMSLR, 4m in the Northern Hemisphere], it’s not centuries, it’s multi-decadal.
This is not maybe the best case, it’s not the worst case.
When I asked Richard Alley, almost certainly the most respected glaciologist in the United States, whether he would be surprised to see Thwaites collapse in his lifetime, he drew a breath. Alley is 58.
‘‘Up until very recently, I would have said, ‘Yes, I’d be surprised,’ ’’ he told me. ‘‘Right now, I’m not sure. I’m still cautiously optimistic that in my life, Thwaites has got enough stability on the ridge where it now sits that I will die before it does. But I’m not confident about that for my kids. And if someday I have grandkids, I’m not at all confident for them.’’
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