IMAGE: NASA

John Bohannon writing for ScienceNOW Daily News, 6 February 2007 files a story that involves the British Antarctic Survey and the Royal Research Ship James Clark Ross.

Admiral Sir James Clark Ross also has the melting Ross Ice Shelf named for him.

The warming of climate via humanity's contributions interest Antarctic Research scientists who would like to get a good idea of "when" these huge ice sheets and glaciers are likely to break loose of the land and slip into a rising sea level and contribute even more to the ocean's rise.

The RRS Ross has now dropped anchor at the Rothera research station, located on the Antarctic Peninsula. The scientists are flying back home today via Punta Arenas, Chile.

As they were about to drop anchor the researchers e-mailed one last dispatch. Their first report included images from the remotely-controlled vehicle Isis at a depth of 3500 meters(11,500 feet), the deepest water dive ever in the Southern Ocean. That research concerned Antarctica's geologic past. The second message intimates the finding of evidence of a biological invasion in the making.

The final word sent from the Ross concerns the future.

One undoubted consequence of climate change is the possibly major rise in the oceans level. How high, and how fast? This sea level rise absolutely depends on how much ice will slide from its perch on continental bedrock into the oceans. And when. Scientists have had great difficulties analyzing what causes glaciers to break away from land because access to the bottom where the connection to the land and the action is -- just isn't easy.

Rob Larter, a marine geophysicist with the British Antarctic Survey at the University of Cambridge in the U.K. writes, "All proposed mechanisms for fast glacier flow require an ample supply of water at the ice bed." Sonar imaging has revealed what look like meltwater channels beneath the Antarctic ice sheet. Last year, researchers spotted signs of water moving beneath the Antarctic ice sheet in satellite data. Why is it so hard to study the base of ice sheets?

The Antarctic ice sheet is up to 4,000 meters(over 13,100 feet)thick and this thickness hampers the use of seismic and other geophysical probes. Only a few very expensive holes have ever been drilled into the ice's land-settled bed.

10,000 years ago, (some reseasrchers say it was 14,200 years ago) the Antarctic glaciers retreated rapidly from some parts of the Antarctic continental shelf, leaving the ice sheet bed, the bedrock connection, perfectly preserved, but under 500 meters(1600 feet) of water. To see what this old bed could tell, Isis visited the bottom of the ice sheet's leading edge last week for an upclose look.

The images from that look offer the first views of "ice streams" (rivers of fresh water) flowing beneath the Antarctic glaciers and pouring into the ocean. The meltwater has carved channels into the bedrock, so it has been flowing for a while. Larter says, "What we have found is one piece of the machinery that operates in large ice sheets, which puts us one step nearer being able to reliably model how they behave."

With a single image, all models of ice flow that do not include subglacial water can now be ruled out. (Most models do, however). The implications for predicting sea level changes will take some time to sort out, Larter says.

All of this kind of research will be pieced together to perhaps give us all a better understanding of when to expect major rises in sea level, and how much those rises will be. The ocean floating ice shelfs themselves only constitute 2% of the Antarctic ice, or roughly 140,000 cubic miles of ice by volume, depending on whose volume computations you work with. If the ice sheets were to melt the contribution to sea level would not be much, since the oceans volume is about 326,000,000 cubic miles of water, with a surface area of 139,500,000 square miles.

That is not the issue. The melting of the floating or loosely connected ocean supported Ice Sheets has no large effect on the rise of sea level,though it does have an effect in holding back the huge continental anchored volumes of ice. The ocean floating glacial tongues mostly, are floating in the ocean already, and sea level is where it is because the ocean is floating these ice sheets. [The ice cube floating and melting in your scotch and water does not overflow the glass containing it.] The real effect is the glaciers behind and above the partially-bedded floating ice sheets -- those huge and ancient glaciers that will have a substantial volume contribution to make. How well-grounded they are and when they will ever be lubricated enough to slide into the sea, is the issue. Some computations -- with all the ice on earth melted -- indicate a rise of 200 to 300 feet in sea level. That much rise floods California's central valley, and Florida becomes a memory (again.)

See a related story.
http://www.xomba.com/making_glaciers_move_part_ii_four_new_lakes_under_the_antarctic_glaciers_vast_rivers_and_streams_contained_beneath_the_ice