Researchers attribute thinning of Greenland glacier to ocean warming preceded by atmospheric changes
September 29, 2008The sudden thinning in 1997 of Jakobshavn Isbræ, one of Greenland's largest glaciers, was caused by subsurface ocean warming, according to research published in the journal Nature Geoscience. The research team traces these oceanic shifts back to changes in the atmospheric circulation in the North Atlantic region.
The study, whose lead author was David Holland, director of the Center for Atmosphere Ocean Science, part of New York University's Courant Institute of Mathematical Sciences, suggests that ocean temperatures may be more important for glacier flow than previously thought.
The project also included scientists from the Wallops Flight Facility, Canada's Memorial University, the Danish Meteorological Institute, and the Greenland Institute of Natural Resources.
Jakobshavn Isbræ, a large outlet glacier feeding a deep-ocean fjord on Greenland's west coast, went from slow thickening to rapid thinning beginning in 1997. Several explanations have been put forward to explain this development. The scientists in the Nature Geoscience study sought to address the matter comprehensively by tracing changes in ocean temperatures and the factors driving these changes.
In doing this, they relied on previous results published by others that used NASA's Airborne Topographic Mapper, which has made airborne surveys along a 120-kilometer stretch in the Jakobshavn ice-drainage basin nearly every year since 1991. While many other glaciers were thinning around Greenland, these surveys revealed that Jakobshavn Isbræ thickened substantially from 1991 to 1997. But, after 1997, Jakobshavn Isbræ began thinning rapidly. Between 1997 and 2001, Airborne Topographic Mapper surveys showed an approximately 35-meter reduction in surface elevations on the glacier's 15-kilomater floating ice tongue. This is far higher than thinning rates of grounded ice immediately upstream.
The researchers reported that these changes coincided with jumps in subsurface ocean temperatures. These temperatures were recorded by the Greenland Institute of Natural Resources from 1991 to 2006 over nearly the entire western Greenland continental shelf. These data indicate a striking, substantial jump in bottom temperature in all parts in the survey area during the second half of the 1990s. In particular, they show that a warm water pulse arrived suddenly on the continental shelf on Disko Bay, which is in close proximity Jakobshavn Isbræ, in 1997. The arrival coincided precisely with the rapid thinning and subsequent retreat of Jakobshavn Isbræ. The warm water mass remains today, and Jakobshavn Isbræ is still in a state of rapid retreat.
The remaining question, then, is what caused the rise in water temperatures during this period.
The researchers traced these oceanic changes back to changes in the atmospheric circulation in the North Atlantic region. The warm, subsurface waters off the west Greenland coast are fed from the east by the subpolar gyre—or swirling water—of the North Atlantic, by way of the Irminger current. The current flows westward along the south coast of Iceland. Since the mid-1990s, observations show a warming of the subpolar gyre and the northern Irminger Basin, which lies south of Greenland. The researchers attributed this warming to changes in the North Atlantic Oscillation (NAO), which is a large-scale fluctuation in the atmospheric pressure system situated in the region. The surface pressure drives surface winds and wintertime storms from west to east across the North Atlantic affecting climate from New England to western Europe.
Specifically, they noted a major change in the behavior of the NAO during the winter of 1995?, which weakened the subpolar gyre, allowing warm subpolar waters to spread westward, beneath colder surface polar waters, and consequently on and over the west Greenland continental shelf.
"The melting of the ice sheets is the wild card of future sea level," Holland explained, "and our results hint that modest changes in atmospheric circulation, possibly driven by anthropogenic influences, could also cause future rapid retreat of the Antarctic Ice Sheet, which holds a far greater potential for sea level rise."
Source: New York University
Oct 31, 2009 |
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I still disagree that it's due to atmospheric changes. Considering the recent discoveries of seafloor ocean warming, and sub glacial tectonic process it looks like AGW may be dealt a significant blow in regard to ice cap melt.
Unfortunately for your theory, the ice is also melting in areas away from contact with the water. Oops.
Unfortunately for your theory, melt is happening in a lot of different places with a lot of different environments, i.e. some in contact with the ocean, some not, some near tectonic processes, some not. In order to "deny" GW, you've got to invoke a grab-bag of alternative processes, many of which aren't actually much in evidence. Your constant harping smacks of post-hoc rationalization. But then, why should you be different from any other denialist?
BTW, I really like Bazz's comment. It really hits the nail right on the thumb.
While I am aware of the seafloor warming processes which you reference and agree that they may have a significant role in ocean temperatures in certain regions that does not rule out the possibility of atmospheric changes affecting ocean temperatures in a significant way.
1)Ocean currents have a major affect on ocean temperatures.
2)Weather patterns are a major driver of ocean currents (and vice versa)
3)If a significant change in a major weather patter (NAO) is accompanied by a change in currents (subpolar gyre) then it is certainly possible that the current was affected by the changing weather pattern as per #2
4) If this is the case see #1
I think that all possible phenomenon should be investigated as contributors; not as the sole cluprit. I'm not saying whether or not I subscribe to AGW b/c this post is long enough but i will say its existance is not neccessary for a change in weather patterns. The source of the change in NAO is a different topic.
That being said I'm no meteorologist although I do live with one :-D.
Before I get to the above quote:
D666: I'm aware there are multiple locations with no oceanic contact that are still experiencing melt, and some of those are located away from known tectonic hotspots. Perhaps I was a bit too vague in describing a main reason for this particular ice melt. I don't discount the potential of atmospheric warming but I do not believe that it's AGW based as I haven't seen enough evidence to prove AGW, let alone it's probable effects.
Bazz: You've gone from contribution to slander, that's unfortunate.
and finally
GIR: Agreed, my statement of oceanic warming was too simplistic. I know of the atmospheric interactions with oceanic current in so far that there is data. I also very much agree that everything should be investigated as opposed to a serial focus on a single aspect with less ample causation for the perceived effect.
Also, Bazz's comment does not appear to be criticizing the original comment as the GW nazi seems to think. From what I can see, he may be making a joke that these "scientists" have their mind (yes, that is singular) made up and will not change it just because somebody points out some inconsistencies or problems they see with it. Seems more a comment on the rigidity of the "researchers'" thought processes than on shortcomings in the commenter's argument.
I think you have a different idea about slandering than i have, your representation of enviromental groups ,scientific groups and governmental groups could arguably be slanderous.
My silly comments on your silly comments would be considered satire ,or if you dont get the underlying joke ridicule.
So far i dont feel bad about it at all, its only fair imo.
String Theorist question General Relativity, that doesn't make them wrong it's scientific progress.
Pursuing one answer to the exclusion of all others is a great way for the scientific community as a whole to fall behind.
I know I appear very skeptical of AGW, and I am, but that doesn't mean they should stop looking for conclusive proof, this is certainly an avenue that could be followed and either create or eliminate evidence. Either way it should be pursued rather than shelved as proof one way or the other.
The only thing they appear to be saying definitivly is the glacier in question has been melting quickly since 1997 and that relates directly to a warmer subsurface current. I'm with them on that so far. That makes sense.
Saying, "possibly driven by anthropogenic influences" is posing a hypothesis. Test it.
Prove it or show consistent cause effect relationships. Then it becomes a law or a theory.
Chicken or the egg? Ocean currents are often the driving factor for the weather.
Think about it. Warm ocean currents create different pressure zones and different wind currents, thus affecting the weather in that location.
That is why i stated
"2)Weather patterns are a major driver of ocean currents **-->(and vice versa)possibleas per #2
I tried to account for currents driving weather patterns with statements like vice versa and possible. Sorry if i wasn't clear.
Chicken or egg:
The article says NAO affected gyre.
"Specifically, they noted a major change in the behavior of the NAO during the winter of 1995?, which weakened the subpolar gyre"
P.S. I think the egg came first. Since I subscribe to evolution I believe that the chicken evolved from a very closely related ancestor. At some point an egg was laid with enough genetic variation from the parent to contain a chikcen. :-P
While some people tend to always look at every situation and see the glass as half empty I prefer to look at it as a glass half full.
Depends, are you measuring from the top, middle or bottom of the miniscus.
It meant to comment on the "half glass full" metaphore, but i guess you either didnt understand or didnt like what i meant and tried to take it as an absolute statement in order to maintain the status quo you made an impressive statement that was not applicable.
What does the shape of the water matter if the glass is 50% liquid and 50% non liquid?You might as well have pointed out that liquids evaporate constantly, the non liquid part cotains tiny droplets or the liquid contains tiny gas bubbles.
You may even point out that there can always be expected to be solid impurities.
So whats going on you didnt get my point or you didnt like my point?