Posted on 03/25/2008 11:02:27 AM PDT by NormsRevenge
A vast ice shelf hanging on by a thin strip looks to be the next chunk to break off from the Antarctic Peninsula, the latest sign of global warming's impact on Earth's southernmost continent.
Scientists are shocked by the rapid change of events.
Glaciologist Ted Scambos of the University of Colorado was monitoring satellite images of the Wilkins Ice Shelf and spotted a huge iceberg measuring 25 miles by 1.5 miles (41 kilometers by 2.5 kilometers - about 10 times the area of Manhattan) that appeared to have broken away from the shelf.
Scambos alerted colleagues at the British Antarctic Survey (BAS) that it looked like the entire ice shelf - about 6,180 square miles (16,000 square kilometers - about the size of Northern Ireland)- was at risk of collapsing.
David Vaughan of the BAS had predicted in 1993 that the northern part of the Wilkins Ice Shelf was likely to be lost within 30 years if warming on the Peninsula continued at the same rate.
"Wilkins is the largest ice shelf on the Antarctic Peninsula yet to be threatened," he said. "I didn't expect to see things happen this quickly. The ice shelf is hanging by a thread - we'll know in the next few days and weeks what its fate will be."
Aircraft reconnaissance
The BAS scientists sent an aircraft out on a reconnaissance mission to survey the extent of damage to the ice shelf.
Jim Elliot, who captured video of the breakout said, "I've never seen anything like this before - it was awesome. We flew along the main crack and observed the sheer scale of movement from the breakage. Big hefty chunks of ice, the size of small houses, look as though they've been thrown around like rubble - it's like an explosion."
An initial iceberg calved away from the Wilkins Ice Shelf on Feb. 28. A series of images shows the edge of the ice shelf proceeding to crumble and disintegrate in a pattern characteristic of climate-caused ice shelf retreats throughout the northern Antarctic Peninsula. The disintegration left a sky-blue patch of hundreds of large blocks of exposed old glacier ice floating across the ocean surface.
By March 8, the ice shelf had lost just over 220 square miles (570 square kilometers) of ice, and the disintegrated ice had spread over 540 square miles (1,400 square kilometers). As of mid-March only a narrow strip of shelf ice between Charcot and Latady islands was protecting several thousand more kilometers of the ice shelf from potentially breaking up.
The region where the Wilkins Ice Shelf lies has experienced unprecedented warming in the past 50 years, with several ice shelves retreating in the past 30 years. Six of these ice shelves have collapsed completely: Prince Gustav Channel, Larsen Inlet, Larsen A, Larsen B, Wordie, Muller and the Jones Ice Shelf.
Antarctic warming
The Wilkins Ice Shelf was stable for most of the last century until it began retreating in the 1990s. A previous major breakout occurred there in 1998 when 390 square miles (1,000 square kilometers) of ice was lost in just a few months.
"We believe the Wilkins has been in place for at least a few hundred years, but warm air and exposure to ocean waves are causing it to break up," Scambos said.
The Antarctic Peninsula has warmed faster than anywhere else in the Southern Hemisphere; temperature records show that the region has warmed by nearly 3 degrees Celsius during the past 50 years - several times the global average and only matched in Alaska.
Other parts of Antarctica, including the East Antarctic Ice Sheet, seem to be more stable, though areas of melt have been observed in recent years.
Melting in the Antarctic is different than the recent record melt in the Arctic. Antarctica is composed of ice sheets, or huge masses of ice up to 2.5 miles (4 kilometers) thick that lie on top of bedrock and flow toward the coast, and ice shelves, the floating extensions of ice sheets. Arctic ice is primarily sea ice, some of which persists year-round and some of which melts in the summer and freezes again in the winter.
This is wayyyy out of my field, but I looked it up, and apparently an ice shelf is very different from normal sea ice. An ice shelf is a glacier that has flowed out onto the water, and it is much stronger than sea ice and therefore CAN and does bottle up glacial ice on land behind it. If you can find someone who actually knows what he's talking about here, I'd defer to them.
How can they call themselves scientists, and at the same time be shocked that changes occur to ice shelves on Planet Earth? This world is constantly in flux, undergoing change.
Before you try with Northern Ireland, I propose we tow something smaller and more manageable... the Gaza Strip.
I recall a movie with Richard Pryor where someone tries to get his character to invest in a scheme to attach engines to icebergs and float them to the Middle East for drinking water.
Yep, 90% of ice shelf is under water, thus displacing water like a ship. the melting ice should just “fill in the hole” where the iceshelf was floating, thus no increase in sea level. Just like filling a glass with ice and water — and after the ice melts, the water level is lower than when it was solid.
Oh yes, the interior of antartica has been getting steadly colder the last decade according to reports these folks ignore reporting about.
Most Glaciers calve as the result of them flowing to the sea. The ice becomes unstable and weakened from warmer summer temperatures. Steep terrain also weakens the ice and gravity does the rest. The volume of ice behind the glaciers has a minimal effect until it rises above the continental terrain and is able to begin moving.
There is also the effects of friction from all that mass and weight. That alone will melt the bottom ice formations and lubricate the mass to aid movement. Add to that the higher subterranean temperatures and geothermal effects from the Earth’s crust, and the ice will melt from below and move where ever it can.
Global Warming being the cause of this much Continental ice mass to move or break up on this level is complete ignorance. This is not ice that is melting from the outside in, it is melting from the bottom up. It is impossible for Global Warming to be the cause. It’s simply a fantastic lie.
This is report from a BBC ice researcher from a year ago around this time:
Ice Station Ronne
Posted on 09/03/07 by Mark Brandon
In my last blog entry I said that I had witnessed dawn over the sea ice.
Of course what I never said was what sea ice actually is……
When the sea surface gets to about -1.8°C it starts to freeze and become solid. (I can’t be any more accurate about the temperature because the more salt in the water, the colder it has to be to freeze). This frozen sea water is called sea ice and it isn’t solid like the ice you put in your drinks from the freezer, but more like a seawater soaked sponge (but not so soggy). Most of the salt is squeezed out of the ice as it forms, but if you put sea ice in your gin or lemonade, then prepare to be very disappointed. New sea ice is probably about 20% as salty as the sea and would make everything taste pretty bad.
Sea ice has been big climate news because we know in the Arctic there is less ice than 50 years ago , and it is also much thinner.In short, in the Arctic the sea ice is on the way out .
In contrast, in the Antarctic we know so little, we cannot really say much. We can measure the area of sea ice (we call this the extent) very easily using satellites. (At this time of year the extent of ice is at a minimum, but it is autumn, -18°C outside and so the extent will increase rapidly). When you look at the sea ice extent data for the Antarctic, the answer we get isn’t clear. In some areas the ice is increasing in extent and in some areas it is decreasing. Overall there is not a significant change (Although in the place I am the sea ice has been retreating). When it comes to the thickness we just don’t have enough measurements to be able to say whether it is changing at all.
So why can we be so certain about the Arctic but know so little about the Antarctic?
Here is a clue .
As part of my research trip we have a scientist on board researching the sea ice. What that means is we have to get off the ship to drill through the ice and collect samples of both the snow and sea ice. This sort of thing is usually done during the day, but conditions have been so good for this kind of work, that Ted Maksym (from the British Antarctic Survey ) took the opportunity to do an ice station at dusk, and as I work nights (we run a 24 hour operation to make the most of our time) I found myself out on the ice.
the calving of ice bergs and segments of continental ice shelves, into nearby waters, is a natural, slow and constant, never ending process, with peaks and valleys in the rate of events at any given time
how and why?
precipitation continually deposits new snow onto existing expanses of ice
over time, under the perpetual continuation of that precipitation, compression compacts the whole into ice-bergs and continental ice packs, with their polar location keeping the whole frozen - on land
the pressure from the compression becomes more and more immense over time, changing the viscosity of the bottom-most layers to a form somewhere between frozen and liquid
the increasing weight of the mass, gravity, the topography of the land and the viscosity of the lower layers results in the bottom seeking to “slide”, where ever gravity directs and topography permits
as with all land-bound water moved by gravity and topography, that eventually leads to the ocean
so, what is the statistical fact, that demonstrates the natural nature of the events reported? - the size and depth of the ice pack lying inland over the whole continent of Antarctica has increased immensely - the whole has increased immensely in size and depth, and so, naturally, has the calving at the warmer-water perimeter at the ocean
“I don’t think there are enough tugboats on the planet to tow an iceberg the size of Northern Ireland.”
I wouldn’t want to write it off as impossible until I had explored the possibility of using ocean currents.
Rather than tugboats, it might be necessary to use something with power more comparable to an aircraft carrier.
Looking out the window, here in balmy Wisconsin, I’d say the glacier is working back down. March 26, 50 degrees and there are still piles of snow from December.
When an ice shelf melts, no sea level rise is experienced; if a huge chunk of earth-bound glacier melts and goes kerplunk, the level rises as it does when you drop an olive in your drink.
This has been going on for as long as we have had explorations there; new snow falls every year and the resultant flow is still about 2mm year total sea rise.
The conditions now are repeated each autumn in the Antarctic.
The concern now is that the overall temperatures are higher than around 1920 or so when we first established stations.
It is also important to notice that the next fundraising go-round is to be held in Bangkok at the end of this month until Apr. 4th.
You are correct, water expands when it freezes (approx 10%). after it melts, it returns to it’s former liquid volume.
The ignorant are often shocked.
Right now the argument about surface temperature versus sea temperature of circulating waters is still an issue to be resolved.
Warmer water melts shore ice and warms the air; warmer air melts surface ice and extends the shelf; clouds come, winter sets in and it snows a lot.
Yep, that is why ice floats. The amount the ice expands is the volume of ice that is above the water level.
Shocked I tell ya. As if all these ice formations are not constantly changing. Now what would be shocking is if they were not changing.
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