Wilkins Ice Shelf

The Wilkins Ice Shelf has been getting a lot of notice for the past while as it appears to be getting more unstable. High resolution work reported here is picking up the substantial cracking underway. This has substantiated the prognosis for a fairly early break up of a large piece of the shelf. Yet this was going to occur anyway.

I am sure a few will try to associate this with global warming but it might be better to associate it with steadily improving observations. This type of science is very much in its boring stage where you need decades of observations to discern patterns or their lack and your role is to gather the first decade or so of data, never been sure what might be important.

At least we will likely get pictures of shelf breakup if as and when it happens.

Of course it is now about to reenter the deep freeze, so it may well just settle down and freeze up good and solid and perhaps not bother us for years.

Northern Ice Front Of Wilkins Ice Shelf Is Becoming Unstable

Bonn, Germany (SPX) May 04, 2009

http://www.spacemart.com/reports/Northern_Ice_Front_Of_Wilkins_Ice_Shelf_Is_Becoming_Unstable_999.html

This image from the European Earth observation satellite ENVISAT is a combination of images taken on 24 and 27 April 2009. This combination of high-resolution TerraSAR-X images and the more frequent, lower-resolution ENVISAT images have given rise to a substantial increase in knowledge, which provides unique insights into the chronological sequence of shelf ice breakaways. Credit: ESA.

http://www.spacemart.com/images/wilkins-ice-shelf-april-09-terrasar-bg.jpg

Following the loss of an ice bridge on the Antarctic Wilkins Ice Shelf, the northern ice front is now becoming unstable. The first icebergs broke off at this point on 20 April 2009.

This was observed by scientists using the TerraSAR-X Earth observation satellite operated by the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR).

"We anticipate that, over the next days and weeks, an area of 570 to 3370 square kilometres will break away before - hopefully - a new and more stable northern ice front will form", states Dr Angelika Humbert, a glaciologist at the University of Munster's Geophysics Institute.

The TerraSAR-X images from 23 and 25 April 2009 show these 'calved' icebergs. These icebergs are breaking away at the failure zones which have gradually formed over the past 15 years.

"The high resolution of TerraSAR-X satellites enables us to observe deformations in the Wilkins Ice Shelf, down to the range of approximately 100 metres," says Dr Humbert, and she goes on to add: "This information enables we glaciologists to describe distortion more precisely with the help of models."

Newly formed cracks are very narrow during their initial stages and are therefore not visible on images taken at a lower resolution, such as those supplied by the older generation of satellites. To reconstruct the chronological sequence of events, the kind of high-resolution images supplied by TerraSAR-X are necessary.

Through an analysis of the chronological development leading to the point where cracks start to appear, an insight into the 'stress conditions' at work in the ice can be gained. Since it started work in 2007, the German Earth observation satellite TerraSAR-X has been supplying scientists with a range of images of the Wilkins Ice Shelf.

"It is in particular the combination of high-resolution TerraSAR-X images and the more frequent, lower-resolution images taken by the European Earth observation satellite ENVISAT (ENVIronmental SATellite) which has provided such a substantial step forward for science, enabling us to gain unique insights into the process of disintegration of an ice shelf," states Dr Humbert.

The Wilkins Ice Shelf is a focal point of the 'Antarctic Background Mission' set up by DLR. The aim of this is to observe changes in the Antarctic ice shelves and to seek to classify the root causes on the basis of all the collated information.

The spectacular break-up events on the Wilkins Ice Shelf in 2008 caused the ice bridge between Charcot and Latady Island, measuring some 40 to 50 kilometres in length, to be cut to a width of just 900 metres at its narrowest point. This plate of ice, only 250 metres thick, finally broke off on 5 April 2008.

Ice shelves are stabilised by the islands adjacent to them, which to a certain extent hold them in check. The loss of this link to Charcot Island will inevitably give rise to instability in the northern ice front of the Wilkins Ice Shelf.

Ice shelves are the floating masses of ice that surround the continent of Antarctica. Some 90 percent of inland ice flows down ice streams and glaciers into these ice shelves. Scientists are of the view that these ice shelves hold back the ice streams and glaciers. However, the precise role played by ice shelves has not yet been fully explained.

The disintegration of the ice shelves reduces this restraining force, causing the movement of ice masses lying behind them to accelerate. This in turn causes more ice to flow into the ocean, causing sea levels to rise. Over the last 30 years, seven ice shelves have retreated across large areas or have completely broken away, causing a loss in surface area amounting to 25,000 square kilometres.

All these ice shelves were located on the Antarctic Peninsula, a region in which temperatures have risen by 2.5 degrees Celsius over the last 50 years - a significantly higher increase than the global average. The Wilkins Ice Shelf, also located on the Antarctic Peninsula, reduced in size during the course of 2008 by some 1800 square kilometres (which equates to about 14 percent of its total area).

In March 2009 - which was prior to the loss of the ice bridge and the current breakup - its area measured 11,200 square kilometres. However, due to the fact that the catchment area further inland is comparably small, this reduction in the size of the Wilkins Ice Shelf will have only a marginal impact on sea level.

The TerraSAR-X mission

TerraSAR-X is the first German satellite that has been manufactured under what is known as a Public-Private Partnership (PPP) between DLR and EADS Astrium GmbH in Friedrichshafen.

The satellite travels around the Earth in a polar orbit and records unique, high-quality X-band radar data about the entire planet using its active antenna. TerraSAR-X works regardless of weather conditions, cloud cover or absence of daylight, and is able to provide radar data with a resolution of down to one metre per pixel.

DLR is responsible for using TerraSAR-X data for scientific purposes. It is also responsible for planning and implementing the mission as well as controlling the satellite. Astrium built the satellite and shares the costs of developing and using it.

2008 Winter Sea Ice Data

This catches us up on the apparent total impact generated by the warming that took place in 2007. It was hardly obvious at the time, but all that warm water ripped into the ability of the sea ice to accrete. A lot less than normal was thus produced this past winter.

Those conditions do not exist this winter, and we are been subjected to a full press arctic chill. It is reasonable to anticipate a full season’s ice production this winter, if not even an increase. 2007 showed us just how quickly the sea ice can be reduced with the right conditions. Had the conditions of 2007 continued, then all the ice would have been easily removed by 2012, as then projected. Once again the weather has changed. Expect to complain about cold winters for a decade at least.

Of course diehards are already claiming that global warming is now preventing the next ice age.

Right now, the right question should be how much further this sudden cooling downswing has to go before it plateaus. Notice I did not say rebound. Rising seems to take a very long time and likely averages less than a tenth of a degree per year, and there is no assurance that it will climb as high as this time.

It would be nice to link this process directly to solar radiation with a high degree of real certainty. That way it would become possible to model other effects properly including CO2. This time around, it looks like the CO2 enthusiasts jumped on the wrong trend and are now having it thrown back in their faces.

http://www.earthportal.org/news/?p=2031

Arctic Sea Ice Is Suddenly Getting Thinner As Well As Receding

Posted on December 19th, 2008

ScienceDaily (Nov. 3, 2008) — Last winter, the thickness of sea ice in large parts of the Arctic fell by nearly half a metre (19 per cent) compared with the average thickness of the previous five winters. This followed the dramatic 2007 summer low when Arctic ice extent dropped to its lowest level since records began.

Up until last winter, the thickness of Arctic sea ice showed a slow downward trend during the previous five winters, but after the summer 2007 record low extent, the thickness of the ice also nose-dived. What is concerning is that sea ice is not just receding but it is also thinning.

Some scientists blamed the record summer 2007 ice extent low on unusually warm weather conditions over the Arctic, but this summer, sea ice extent reached the second lowest level since records began, even though the Arctic had a relatively cool summer. Dr Katharine Giles, who led the study and is based at the Centre for Polar Observation and Modelling at University College London – part of the National Centre for Earth Observation, says: “This summer’s low ice extent doesn’t seem to have been driven by warm weather, so the question is, was last winter’s thinning behind it?”

The team of researchers, including Dr Seymour Laxon and Andy Ridout, used satellites to measure sea ice thickness over the Arctic from 2002 to 2008. Winter sea ice in the Arctic is around two and half metres thick on average. Ice thickness can be calculated from the time it takes a radar pulse to travel from a satellite to the surface of the ice and back again.

The research - reported in Geophysical Research Letters - showed that last winter the average thickness of sea ice over the whole Arctic fell by 26cm (10 per cent) compared with the average thickness of the previous five winters, but sea ice in the western Arctic lost around 49cm of thickness. This region of the Arctic saw the North-West passage become ice free and open to shipping for the first time in 30 years during the summer of 2007.

The team is the first to measure ice thickness throughout the Arctic winter, from October to March, over more than half of the Arctic, using the European Space Agency’s Envisat satellite. Before this, Christian Haas of the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, had discovered thinner ice in a small region around the North Pole. Whilst the overall loss of older, thicker ice led researchers to speculate that Arctic sea ice had probably thinned, this is the first time scientists have been able to say for definite that the ice thinning was widespread and occurred in areas of both young and old ice.

“The extent of sea ice in the Arctic is down to a number of factors, including warm weather melting it as well as currents and the wind blowing it around, so it’s important to know how ice thickness is changing as well as the extent of the ice,” added Giles.