New results from an investigation into Antarctica’s potential contribution to sea level rise are reported this week (Sunday 20 June) by scientists from the British Antarctic Survey (BAS), Lamont-Doherty Earth Observatory (LDEO) and the National Oceanography Centre in the journal Nature Geoscience.
Thinning ice in West Antarctica is currently contributing nearly 10 per cent of global sea level rise and scientists have identified Pine Island Glacier (PIG) as a major source. As part of a series of investigations to better understand the impact of melting ice on sea level an exciting new discovery has been made. Using Autosub (an autonomous underwater vehicle) to dive deep and travel far beneath the pine Island Glacier’s floating ice shelf, scientists captured ocean and sea-floor measurements, which revealed a 300m high ridge (mountain) on the sea floor.
Pine Island Glacier was once grounded on (sitting on top of) this underwater ridge, which slowed its flow into the sea. However, in recent decades it has thinned and disconnected from the ridge, allowing the glacier to move ice more rapidly from the land into the sea. This also permitted deep warm ocean water to flow over the ridge and into a widening cavity that now extends to an area of 1000 km2 under the ice shelf. The warm water, trapped under the ice, is causing the bottom of the ice shelf to melt, resulting in continuous thinning and acceleration of the glacier.
Lead author Dr Adrian Jenkins of British Antarctic Survey said, “The discovery of the ridge has raised new questions about whether the current loss of ice from Pine Island Glacier is caused by recent climate change or is a continuation of a longer-term process that began when the glacier disconnected from the ridge.
“We do not know what kick-started the initial retreat from the ridge, but we do know that it started some time prior to 1970. Since detailed observations of Pine Island Glacier only began in the 1990s, we now need to use other techniques such as ice core analysis and computer modelling to look much further into the glacier’s history in order to understand if what we see now is part of a long term trend of ice sheet contraction. This work is vital for evaluating the risk of potential wide-spread collapse of West Antarctic glaciers.”
[UPDATE]
Steven Mosher has graciously allowed me to add my two cents worth here. As you know, I love data, it beats theories every time.
First, data on the location of the Pine Island Glacier:
Figure W1. Pine Island Glacier, Antarctica. The West Antarctic Peninsula is at the top right. Pine Island Glacier is shown by the snowflake. The white box outlines the area for which I show sea surface temperature (SST) below.
Next, data on the ocean surface temperatures. There are a couple of SST datasets that cover this area. Both are available at KNMI, that amazing resource. One is the Hadley HADISST Ice and Sea Surface Dataset. The other is the Reynolds satellite based dataset. Here’s what they say about the sea surface temperatures in the area outlined by the white box:
Figure W2. Change in sea surface temperature (SST) in the ocean off of Pine Island Glacier.
Conclusions? Well, it seems clear that the change in the sea surface temperature is not the reason for the melting of the Pine Island Glacier, SSTs have been dropping there for the last thirty years …
Regards to all,
w.
John A says:
June 21, 2010 at 2:07 pm
Can someone please explain where “deep warm water” came from?
Warm in relative terms, i.e. warmer than ice, and perhaps warmer than other deep water. But freezing cold anyway. There is besides some suspicion that the circumpolar current may have brought some warm water to Antarctica (hypothesis floated by Steig in 2009) but as Steig recognizes there is no evidence so far.
vukcevic says:
June 21, 2010 at 12:37 pm
Very nicely presented. Now, what makes the Hudson Bay Field fall and the Siberian Field rise?
I dont understand this. The ice in question is floating in water? Right?
So it follows Archinedes law. Right?
So sealevel will neither rise nor decrease when it melts. Right?
Only difference is salinity. Tiiiiiiiiny difference.
@psi June 21, 2010 at 11:32 am:
Let’s see now, should I believe the Huffington Post or BP? That’s not even a coin toss! The Huffington Post agenda is clear for all to see. They aren’t risking their lives and their wealth. They don’t even have any credibility left to risk.
I find it more than a little frustrating that, with claims that ‘the science is settled’, that these ‘scientists’ are forever making new discoveries of Nature’s effects on the world.
Given that the effect on the ice of the 300m ridge was not factored into previous models, estimates, predictions, analyses, et al, will they now retract all of their previous descriptions and/or admit that they were wrong/ill-informed/guessing/etc?
I am just curious but if the ice extended to the floor of the ocean to beyond the ridge mentioned and then melted from the bottom up as the article seems to indicate. Would not the volume of the liquid water be less than the volume of the ice before it melted? If this is true there at least initially should have been a net fall of sea level. Now the question is about the rate of condensation above Antarctica in relation to the rate of evaporation from the sea. I am truly wondering where the problem lies. I seem to remember that at one time sea level was much higher than it is now and for the foreseeable future. Also that it has been some what lower than it is now and for the foreseeable future. Might not this all be with in the bounds of historic levels.
Bill Derryberry
Hector:.
“melting ice shelves do not rise sea level because the ice was already floating (there might be a non significant increase in sea level because a given mass of liquid water has more volume than the same mass in a frozen state). ”
A given mass of liquid water has less volume (higher density,) else ice (frozen state) would not float. I think you meant the other way round?
Only the ice on land can add to the ocean level due to the Archemdes law as pointed out above, so how much of the ice is on land/glacial flowing into the ocean? Percent? what effect would this have if any? Have we seen any effect from the ice which was “grounded” on the ridge and is now floating? Any cities gone?
Am I missing something here. The article seems to indicate that the glacier is floating. How can floating glacier cause sea level rise?
I wonder whether volcanoes might be having some kind of impact.
Thank you Hector M. I was getting the impression tha they wanted to take ice cores from the melting glaciers on Pine Island.
“Deep Warm Water”-Maybe something to do with the Thermohaline circulation upwell circum-Antarctica (just a guess)? This tends to be out-of phase with N. Hemisphere.
However, it cannot explain the more widespread thinning of West Antarctic glaciers that together are contributing nearly 0.2mm per year to sea-level rise.
Ouch. 0.2 mm. That’s enough to cover a sheet of newspaper. Better get the Bounty towels out.
Today’s climate scientists strike me as modern-day Neptunists, grasping at straws to hold onto a view of the earth and its climate as never changing entities — and the changes we see now are solely the result of mankind’s activities. And the skeptics are modern-day Plutonists. Sure hope this analogy holds, as the Plutonist school of thought ultimately helped form geology as we know it today (with a few hiccups along the way).
Here’s a thought to ponder — in the history of geology in which the struggle between Neptunists and Plutonists took place, the matter took a couple centuries to resolve.
Oh that’s just great! Does that mean we’ll have to contend with Al Gore and his acolytes for another century?!!
@Hector M. (June 21, 2010 at 12:49 pm) who says:
“…(there might be a non significant increase in sea level because a given mass of liquid water has more volume than the same mass in a frozen state)….”
Hector, that’s exactly backwards. Ice floats because it is less dense than water. If you freeze one gram of (pure) water (nominally 1.0 cc), it yields ~1.09 cc of ice. (Sea water will yield somewhat different results, but the net effect is the same.)
From a wiki explanation: “One important property of ice is that it expands upon freezing. At 0° C it has specific gravity 0.9168 as compared to specific gravity 0.9998 of water at the same temperature. As a result, ice floats in water.”
@Psi:
You should post your Gulf/methane item here:
http://wattsupwiththat.com/2010/06/21/oil-spills-into-the-debate/
The solution is quite simple, really. Just whitewash the snow, as is proposed for the Andean glaciers.
Why all the fuss?
~Snip~
[Strike one. ~dbs, mod.]
Leon Brozyna says:
June 21, 2010 at 5:00 pm
I can look out my window and see plutons rising to 8,000 feet. Nice snow still on them.
“This work is vital for evaluating the risk of potential wide-spread collapse of West Antarctic glaciers.”
Keeeeer…..ching! or to put it another way…..Please send more grant money!
vukcevic says: “Antarctica’s circumpolar current and associated gyres are to certain extent impeded by the strong magnetic field in the area…”
Then shouldn’t you be able to demonstrate the effect of magnetic fields on such vortices on a laboratory scale?
“The warm water, trapped under the ice, is causing the bottom of the ice shelf to melt, resulting in continuous thinning and acceleration of the glacier”.Would the ice be also cool down the warm water too as it melts?.
I’ve added an update to the head post for those interested in the sea surface temperatures in the area.
w.
A few posters are confusing the effects of sea-ice melting & glacier/ice sheet melts.
Sea ice is formed by the freezing of sea water when its temperature falls below -3C.
Thus the melting of sea ice just returns the water it took from the sea only a matter of a few years previously. So no net rise in sea level.
Glaciers & Ice sheets (essentially the same beast, just scale differences) are formed from compressed snow, thus when they melt, they return to the sea, water that may have been evaporated millenia ago.
Thus a rise in sea level. That’s why there are mammoth bones dredged up from the bottom of the North Sea, which was dry land until the melt that followed the end of the last ice age and sea levels rising a few hundred feet.
“Thinning ice in West Antarctica is currently contributing nearly 10 per cent of global sea level rise”
Run for the hills! it’ a 30 micrometer rise in sea level! /sarc off
Really, are they seriously trying to scare us with 10% of 3.2 mm/year (last count I’ve seen with it having slowed in the last few years)?
“Glaciers & Ice sheets (essentially the same beast, just scale differences) are formed from compressed snow, thus when they melt, they return to the sea, water that may have been evaporated millenia ago.”
Well, let’s finish your thought. There’s more going on than just that. Glaciers are pushed to the sea by the mass of the glacier, and you’ve made it sound like it’s just a chunk of ice sitting there. Not to mention that where the glacer meets the sea, the glacier/ice sheet will increase in size when the temperature drops below -3c, which means no change in sea level from that ice melting. It seems to me that there could be a few things going on here:
1) SST’s increased melting the glaciers faster
2) less percipitation and the glaciers are still melting at the same rate as ever, just the mass is growing less.
3) more precipitation and the glaciers are moving fast to the ocean where they can melt (kind of farfetched)
4) probably some combination of 1 and 2