Role of melt in arctic sea ice loss found by NASA study

Nov 10, 2010 By Kathryn Hansen
A mosaic of satellite images shows the movement of fragmented ice away from ice edges, which scientists use to track the loss of multiyear ice due to melt. Image credit: NASA Earth Observatory

A NASA analysis of satellite data has quantified, for the first time, the amount of older and thicker "multiyear" sea ice lost from the Arctic Ocean due to melting.

Since the start of the satellite record in 1979, scientists have observed the continued disappearance of older "multiyear" sea ice that survives more than one summer melt season. Some scientists suspected that this loss was due entirely to wind pushing the ice out of the Arctic Basin -- a process that scientists refer to as "export." In this study, Ron Kwok and Glenn Cunningham at NASA's Jet Propulsion Laboratory in Pasadena, Calif., used a suite of to clarify the relative role of export versus melt within the Arctic Ocean.

Kwok and Cunningham show that between 1993 and 2009, a significant amount of multiyear ice -- 1,400 cubic kilometers (336 cubic miles) -- was lost due to melt, not export.

"The paper shows that there is indeed melt of old ice within the Arctic basin and the melt area has been increasing over the past several years," Kwok said. "The story is always more complicated -- there is melt as well as export -- but this is another step in calculating the mass and area balance of the Arctic ice cover."

Maps of multiyear sea ice coverage of the Arctic Ocean on April 30, 2008 (left) and again on Nov. 30, 2008 (right) show that a large area of fragmented multiyear ice in the Beaufort Sea disappeared after the ice pack reached its annual summer minimum extent. Image credit: NASA Earth Observatory

The results have implications for understanding how Arctic sea ice gets redistributed, where melt occurs in the Arctic Ocean, and how the ocean, ice and atmosphere interact as a system to affect Earth's climate. The study was published in October 2010 in .

Scientists track the annual cycle of coverage as it melts through the summer to reach a minimum extent each September, before refreezing through fall and winter. Much of that ice is seasonal, meaning that it forms and melts within the year.

But multiyear ice that survives more than one season has also been declining, as noted in previous work by Joey Comiso of NASA's Goddard Space Flight Center in Greenbelt, Md., who shows a loss of about 10 percent per decade since the beginning of the satellite record in 1979. Scientists want to know where this loss is occurring.

"The decline of the multiyear ice cover of the last several decades has not been quantitatively explained," Kwok said.

To investigate the loss of multiyear ice, Kwok and Cunningham looked at a 17-year span of data from 1993 to 2009 from a range of polar-observing satellites and instruments, including NASA's Quick Scatterometer (QuikScat); the Ice, Cloud and land Elevation Satellite (ICESat); the Advanced Microwave Scanning Radiometer (AMSR); and the European Space Agency's European Remote Sensing (ERS)-1 and -2 satellites. Some instruments track ice coverage, while others track motion and concentration.

The team collected satellite images and tracked pixels of multiyear ice from April 1, prior to the onset of seasonal melt, and into the summer. Pixels that deviated away from images of the ice edge were considered lost to melt.

The team compared summertime melt of multiyear ice in the Beaufort Sea with estimates of ice lost from the Arctic basin through the Fram Strait -- a major passage through which ice can exit the Arctic Ocean. The comparison revealed how much multiyear ice was lost to export and how much was lost to melt.

They found that over the 17-year period, an area of 947,000 square kilometers (365,639 square miles), or about 32 percent of the decline in multiyear sea ice area, was lost in the Beaufort Sea due to melt.

A similar calculation using thickness estimates from NASA's ICESat from 2004 to 2009 show a volume loss of 1,400 cubic kilometers (336 cubic miles), or about 20 percent of the total loss by volume.

How and where multiyear ice is lost has impacts on the Arctic system. For example, more loss by melt means more freshwater remains in local Arctic waters rather than being transported southward.

"These results also show that thick multiyear sea ice is not immune to melt in the Pacific sector of the in today's climate," Kwok said.

The additional freshwater from melt in the Pacific sector, which encompasses the area of study, could contribute to the freshening of the Beaufort Gyre and potentially influence circulation, but the degree of that influence remains uncertain.

Not all of the multiyear is accounted for, however. Ice loss through Fram Strait and from melt from 2005 to 2008 accounts for just 52 percent of total ice loss. The team suggests that melt in other Arctic regions and outflow through other passages besides Fram Strait could account for the difference.

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More information: www.nasa.gov/topics/earth/feat… cesat-20090707r.html

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User comments : 13

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rproulx45
4.6 / 5 (9) Nov 10, 2010
Don't let the disappearing ice fool you, global warming is myth, perpetuated by facts,photos, and data. Those clever devils would have us believe what we see and what we can test. Ha! Well I'm smerter than that, you can't fool me so easily!
JimB135
2.7 / 5 (3) Nov 10, 2010
Don't let the disappearing ice fool you, global warming is myth, perpetuated by facts,photos, and data. Those clever devils would have us believe what we see and what we can test. Ha! Well I'm smerter than that, you can't fool me so easily!


The scientists are looking at ice melt and trying to quantify what ice is melting and what ice is being pushed out by wind and you cry global warming myth? Crawl back under your rock you troll.
lengould100
2 / 5 (2) Nov 10, 2010
would have us believe what we see and what we can test. Ha!
Huh? Which side are you actually arguing?
GSwift7
2 / 5 (3) Nov 10, 2010
"Some scientists suspected that this loss was due entirely to wind pushing the ice out "

Can anyone confirm this? I find it hard to believe that any serious scientist would totally rule out melting. I suspect this is an exaggeration.

"a significant amount of multiyear ice ... was lost due to melt, not export"

"about 32 percent of the decline in multiyear sea ice area, was lost in the Beaufort Sea due to melt"

That leaves 68% to export, so in the area studied here, export accounts for more than double the effect of melt? I think the next question they should answer is whether those two processes are accellerating or not, and whether the relative rates vary linearly or not. A change in export rate would have double the effect of a change in melt rate.
Skeptic_Heretic
5 / 5 (4) Nov 10, 2010
Can anyone confirm this? I find it hard to believe that any serious scientist would totally rule out melting. I suspect this is an exaggeration.
I can. Export is a well founded mechanism for multiyear ice loss. The primary question was whether we were actually losing any to melt as opposed to export and replacement. Unfortunately this study appears to lend creedence to the observations of surface heating of the oceans in the regions recorded. Whether this is AGCC or not remains to be seen, but a warmer ocean is certainly something not entirely accounted for.

As was said above "the melt hasn't been quantitatively disposed".
That leaves 68% to export, so in the area studied here, export accounts for more than double the effect of melt?
Well no, don't forget, this is a measurement of area, not volume or mass. Multiyear ice is rather adept at becomming more dense, decreasing the area, but not affecting total mass. Export falls in there, but I can't speak to extent.
StillWind
1 / 5 (5) Nov 10, 2010
Rising ocean temps disprove AGW, so just more of what many of us already know.
GSwift7
4.3 / 5 (3) Nov 10, 2010
"Rising ocean temps disprove AGW, so just more of what many of us already know"

Can you explain the logic of this? I can see how it would lessen the effect of man made GHG's but I hardly see that it completely eliminates the effect. I think the magnitude of ocean warming has to be taken into account, and warming at the North Pole doesn't equate to warming of the ocean as a whole. There is also a difference between surface warming and warming at depth.
thermodynamics
5 / 5 (1) Nov 11, 2010
rproulx45: I must admit that you are clever enough to have caught a couple of readers thinking you were serious instead of being ironic. I guess that most people just don't have a sense of humor about such a serious subject, but I have to smile about the problems we face now and then or I would be depressed. Instead, an occasional smile from a subtle joke keeps me going.

Your concept of facts, photos, and data being the basis for the "myth" is outstanding. My hat is off to you. I was ROFL.

Having heard similar words from marjon and others when they were serious, it was great to see the words turned back the way they should have been. Great work.
thermodynamics
5 / 5 (1) Nov 11, 2010
StillWind: Can you please explain the science of your (now famous) statement:

"Rising ocean temps disprove AGW, so just more of what many of us already know."

I am very interested in seeing references and papers along these lines. I have to admit it is part of the science I do not understand and I would very much like to be educated along those lines. Thank you in advance for the links and information you will be sending our way.
GSwift7
5 / 5 (1) Nov 11, 2010
Thermo, I've heard this line of reasoning before and it makes sense a little bit, if it were true. It's really just a hypothetical line of reasoning, but if the oceans actually had gotten significantly warmer already then it would preclude human influence because of timing and other issues. In reality, warming in certain places is balanced by cooling in others to produce only a small global variation in ocean temp, so AGW theory is safe from that threat as far as I know.

If the ocean had warmed already, then trying to say that atmospheric warming had caused it would be like saying that your flea is infested with dog. If the atmosphere is warming, then it should take centuries for the ocean to catch up and warm as well. Ironically, warming atmosphere may have an initial cooling effect on oceans because of the combined effects of increased precipitation, increased evaporation, and cold meltwater inflow. Ocean temp controls air temp more than the other way around.
Skeptic_Heretic
5 / 5 (1) Nov 11, 2010
Ironically, warming atmosphere may have an initial cooling effect on oceans because of the combined effects of increased precipitation, increased evaporation, and cold meltwater inflow. Ocean temp controls air temp more than the other way around.
Yes but the problem with this reasoning is that land temp affects ocean temp far greater than ocean temp affects land temp. If the retention of heat in the atmosphere increases that creates a lag in the convection from land to air and makes the ocean a greater sink of heat. Neither effect really lends to AGCC or detracts from AGCC.
MatthiasF
5 / 5 (1) Nov 14, 2010
Oceans = 1.4 x 10^21 kg
Atmosphere = 5 x 10^18 kg

Seems to me change in ocean temperature would be a bigger deal than atmospheric temperatures. Since it possibly represents an amount of energy 280 times greater.
GSwift7
5 / 5 (1) Nov 14, 2010
"Yes but the problem with this reasoning is that land temp affects ocean temp far greater than ocean temp affects land temp. If the retention of heat in the atmosphere increases"

No, the point is that changes in surface temperature dominate, whether it's land or ocean. Any heat retained by the atmosphere is ratidated from the surface, whether it's land or sea. Neither the land nor the sea will change temperature very quickly compared to the air. And, before you start talking about cummulative effects of changes in ghg's in the air, I would propose an analysis of cummulative effects of changes in surface temperatures, such as those caused by concrete and asphalt. I'm not buying the proposition that a small change in air temp will have any profound effect on surface temps.

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