Sane response to press release

Shock horror! Worlds press responds sensibly to a press release. Well it was one of ours, and the response seems to be to ignore it, which is fair enough. But a touch surprising, since its yet another iceberg breaking off Antarctica (this one half the size of London, the latest unit of measurement). Read all about it. Probably the problem is the third para: "This calving event is part of a natural cyclic process. A 34-year long study of the glacier has shown that a large iceberg breaks off roughly every 5-10 years. The last was in 2001."

More like this

I thought the largest unit of measurement was a "Wales"? Though a London seems more appropriate here.

Wait -- the glacier is thinner, and moving to the sea faster.

That doesn't contribute to sea level change? Or do you mean that the actual breaking off of the iceberg doesn't contribute to any instantaneous sea level change?

[The latter I presume -W]

"The location at which the glacier starts to float on the sea also retreated at a rate of more than 1 km/year during part of this period."

What happened under there? The ice is thinner and moving faster so it's peeling off higher on the land surface, just not sticking as well? Less traction at high speed?

The ocean's risen a millimeter and the underlying land is very very flat?

The ocean's warm enough to have melted back underneath the ice where the ice was grounded below sea level?

[Errrm well, bits of all perhaps. Its probably melting. But the land has a reverse slope there (or thereabouts) which is whats behind the good old unstable W Ant theory -W]

Does this mean an entire kilometer per year of the glacier is now developing those flexing cracks going up and down with the tides, the ones usually found right at the grounding lines?

What's puzzling is the release says so many things have changed, and then says the one thing that hasn't changed is the frequency at which some ice with a large surface area breaks off.

What about the volume of ice breaking off, has that decreased because the glacier's thinner per surface area?

Thinner, less massive icebergs happening in Antarctica...?"

By Hank Roberts (not verified) on 23 Oct 2007 #permalink

When a grounding line retreats, that ice changes from being a 'glacier' to being an 'ice shelf' for the area no longer grounded? I don't recall how wide Pine Island is.

Is floating ice any more at risk of a Larsen-type breakup than grounded ice, as tidal stresses accumulate over time?

[The Larsen was floating. Non-floating isn't vulnerable. If the Larsen was due to tidal, its passed me by (how could it be - the tides haven't changed -W]

Does the reverse slope means this ice, although floating, is doing so over protected water (a 'sound' behind 'outer banks' in North Carolina terms) -- so would be less exposed to the kinds of variations in sea level over short terms than if it were out over the open ocean?

How about less susceptible to warmer water currents?

Hmmm ... anyone checking salinity under the ice? Is it more meltwater or is it well mixed ocean water under there?

[Funny things happen under the ice shelves, as they can melt from below, and odd things happen to the water density -W]

Fascinating. Making any bets on what it does next?
30-odd years is a bit short for deciding how regularly it breaks up, I'd suspect, unless it's a typical behavior based on more than the one glacier.

Pardon the many questions, and feel free to bring out the clue bat if I'm asking dumb ones, help me ask smarter ones if it seems worthwhile.

By Hank Roberts (not verified) on 23 Oct 2007 #permalink

I'm recalling mention of stress cracks happening at the grounding line on floating ice sheets; when the grounding line retreats, I'd imagine the stress cracks would develop above the new 'hinge' line as it moves. They apparently fill up with loose debris rather than rehealing.

"Deep south, Pine Island Glacier accelerated 38 percent from 1974-2005, and its yearly acceleration rate increased fivefold...."

Last time I bothered knowledgeable people about this was over at Prometheus…

The excerpts are over there if anyone wants more to start updating from. It was all new news then and the Int'l Polar Year stuff should be bringing more news steadily.…


Reuters - Dec 20, 2006
- Tides affect the speed at which an Antarctic ice sheet bigger than the Netherlands is sliding toward the sea ....
The Rutford Ice Stream ...rate varies 20 percent in tandem with two-week tidal cycles, ... even on ice more than 40 km (25 miles) inland. "... we didn't know it happened on this two-weekly time scale," said Hilmar Gudmundsson, an Icelandic glaciologist at the British Antarctic Survey.

By Hank Roberts (not verified) on 23 Oct 2007 #permalink

Here some interesting observations on iceberg drift from the 1890's to 44 s


Some recent research on iceberg drift to the same location during the last glaciations. When sea levels were 100 meters lower.

And some interesting observations on Greenland glaciers from 1874,with some interesting comment on the thermodynamics referenced to one Professor Thompson.

"This flow of water, Geikie thinks, probably circulates to some extent below every glacier, and he accounts for it by the liquefaction of ice from the warmth of the underlying soil. I am sure you will find a more natural solution of this flow of water from glaciers--estimated not less than 3000 feet thick--in the suggestion first made by Professor James Thomson, and subsequently proved by his brother, Professor W. Thomson, that the freezing point of water is lowered by the effect of pressure 0.23° Fahr., or about a quarter of a degree for each additional atmosphere of pressure. Now, a sheet of ice 3000 feet thick is equal to a pressure of eighty-three atmospheres, at which pressure it would require a temperature of 19° below freezing point to retain the form of ice.

By maksimovich (not verified) on 23 Oct 2007 #permalink

re: the large icebergs that break off every 5-10 yrs

do we/you/they have good estimates of the sizes over the last 34 years? are they roughly the same size? getting smaller?

the picture was pretty neat to look at, it had some impressive tracks.

[We should have satellite imagery of the coastline since ~1980, so a good idea of whats broken off since then -W]