Research into carbon storage in Arctic tundra reveals unexpected insight into ecosystem resiliency

May 16, 2013
This image shows the US Arctic LTER greenhouse in peak autumn and early winter. Credit: Sadie Iverson (autumn), and Josh Schimel (winter)

When UC Santa Barbara doctoral student Seeta Sistla and her adviser, environmental studies professor Josh Schimel, went north not long ago to study how long-term warming in the Arctic affects carbon storage, they had made certain assumptions.

"We expected that because of the long-term warming, we would have lost carbon stored in the to the atmosphere," said Schimel. The gradual warming, he explained, would accelerate decomposition on the upper layers of what would have previously been frozen or near-frozen earth, releasing the into the air. Because contain nearly half of all global in their ancient permafrost –– permanently frozen soil –– even a few degrees' rise in temperature could be enough to release massive quantities, turning a carbon repository into a carbon emitter.

"The Arctic is the most rapidly warming biome on Earth, so understanding how permafrost soils are reacting to this change is of major concern globally," Sistla said.

To test their hypothesis, the researchers visited the longest-running climate warming study in the tundra, the U.S. Arctic site at Toolik Lake in northern Alaska. This ecosystem-warming greenhouse experiment was started in 1989 to observe the effects of sustained warming on the .

What they initially found was typical of Arctic warming: low-lying, shallow-rooted vegetation giving way to taller plants with deeper roots; greater wood shrub dominance; and increased thaw depth. What they weren't expecting was that two decades of slow and steady warming had not changed the amounts of carbon in the soil, despite changes in vegetation and even the soil .

The answer to that mystery, according to Sistla, might be found in the finer workings of the ecosystem: Increased plant growth appears to have facilitated stabilizing feedbacks to soil . Their research is published in the recent edition of the journal Nature.

"We hypothesize that net soil carbon hasn't changed after 20 years because warming-accelerated decomposition has been offset by increased carbon inputs to the soil due to a combination of increased plant growth and changing soil conditions," Sistla said.

The increased plant productivity, caused by the warmer temperatures –– on average 2 degrees Celsius in the air and 1 degree in the soil to the permafrost –– has increased plant litter inputs to the soil. Unexpectedly, the soils in the greenhouse experiment developed higher winter temperatures, while the summer warming effect declined.

"These changes reflect a complicated feedback," Sistla said. "Shrubs trap more snow than the lower-lying vegetation, creating warmer winter soil temperatures that further stimulate both decomposers and plant growth. Shrubs also increase summer shading, which appears to have reduced decomposer activity in the surface soil by reducing the greenhouse effect during the summer."

The increased plant growth and deeper thaw, meanwhile, also may have enabled increased carbon availability in the deeper mineral layer that overlies the . In fact, the researchers found the strongest biological effects of warming at depth, a "biotic awakening," with mineral soil decomposers showing more activity, along with the increased carbon stock at that level. "It's a surprising counterbalance," said Schimel. "It may be that those soil systems are not quite as vulnerable to warming as initially expected."

However, whether or not this phenomenon –– no net loss of soil carbon despite long-term warming –– is a transient phase that will eventually give way to increased decomposition activity and more carbon release, is not yet known. Future studies will include investigation into the mineral soil to determine the age of the carbon, which may in turn yield clues into how the carbon cycle is changing at depth, where the majority of tundra soil carbon is stored.

Funding for this study came from the National Science Foundation Long Term Ecological Research (LTER) Program, DOE Global Change Education Program Graduate Fellowship, a Leal Anne Kerry Mertes scholarship, and Explorer's Club.

According to Sistla and Schimel, this research paradigm validates the NSF LTER program's commitment to supporting long-term experiments, because it creates opportunities for younger scientists to observe effects and condition decades after experiments are established –– results that could not have been foreseen when the experiments were started.

Explore further: Fracking raises concerns among community leaders, study indicates

More information: dx.doi.org/10.1038/nature12129

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User comments : 13

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MR166
1.9 / 5 (14) May 16, 2013
The very fact that I am alive and able to post this comment is a living testament to the fact that the ecosystem is resilient and not prone to positive feedback extremes. The earth has seen CO2 levels 10x greater than today's levels and has not plummeted " Over the edge."! How much evidence does it take for the warmists to acknowledge that they are victims of an out of control political system?????
deepsand
3.3 / 5 (16) May 16, 2013
The very fact that I am alive and able to post this comment is a living testament to the fact that the ecosystem is resilient and not prone to positive feedback extremes. The earth has seen CO2 levels 10x greater than today's levels and has not plummeted " Over the edge."! How much evidence does it take for the warmists to acknowledge that they are victims of an out of control political system?????

The only thing that your posting here proves is that you are fortunate to exist in a place and at a time that affords you the luxury of being able to waste time and energy on your activities here.
Howhot
4 / 5 (8) May 16, 2013
How much evidence does it take for the warmists to acknowledge that they are victims of an out of control political system?????
In all fairness if your turn that question around it makes you wonder what the political agenda of that guy is.
MR166
1.8 / 5 (10) May 17, 2013
"In all fairness if your turn that question around it makes you wonder what the political agenda of that guy is."

In a nutshell, I would like to see a return to individual freedom and responsibility, the returning of property rights and a smaller less intrusive government on every level.
Neinsense99
3.2 / 5 (9) May 19, 2013
" return to individual freedom and responsibility, the returning of property rights and a smaller less intrusive government on every level."

Another Randite fantasy about fair and equal opportunity -- just so long as THEY get to start from the front row or pole position, taking advantage of historical actions, including government measures. Ever wonder why you don't see many native Americans promoting libertarian ideas, other than a few sellouts bucking for smoke-and-mirror positions?
MR166
1.4 / 5 (9) May 19, 2013
Meanwhile Nien, your Marxist utopian friends have killed 100 million people in pursuit of their dreams. Everyone is equal unless you cannot add the the wealth of the state------then you are starved to death.
Howhot
4.3 / 5 (6) May 20, 2013
In a nutshell, I would like to see a return to individual freedom and responsibility, the returning of property rights and a smaller less intrusive government on every level.
That is sad. So your life is simply about your own greed? You have all of the property rights in to world to do what ever you want. However, you do not have the right to pollute my land while you destroy yours. And government isn't intrusive enough on you kind. What are you trying to hide on your land that you need all of privacy? Something criminal? Something damaging the environment like dumping barrels of dioxin into a stream on your land? And your kind dares calls us Americans... Marxist? You POS!

MR166
1.6 / 5 (9) May 20, 2013
Howhot you should do a little reading on our president and see who his heroes were in college.
Neinsense99
3 / 5 (8) May 20, 2013
Meanwhile Nien, your Marxist utopian friends have killed 100 million people in pursuit of their dreams. Everyone is equal unless you cannot add the the wealth of the state------then you are starved to death.


A baseless assumption about my political beliefs, to start, and you don't even come close to addressing my point in a rational way. When it hits too close to home, drag in Stalin, eh?
MR166
1 / 5 (7) May 20, 2013
Nien don't forget to give credit to Chairman Mao and his purges. BTW here is a little tidbit on his Granddaughter. http://www.telegr...ist.html

Perhaps she earned this money dispensing Slurpees at 7-11.

We need smaller less intrusive governments because both sides are owned by the same powerful people who write the laws to benefit themselves. The less power we give the governments the less power the few have to enslave us.
MR166
1 / 5 (6) May 22, 2013
Lastly, if the US IRS scandal does not strike fear into the hearts of every citizen then we are too ignorant to deserve to be free.
Neinsense99
3.3 / 5 (7) May 25, 2013
"Lastly, if the US IRS scandal does not strike fear into the hearts of every citizen.."
I doubt the average citizen in Oslo, Buenos Aires or Montreal would be very concerned at all.
deepsand
3.2 / 5 (11) May 25, 2013
Does MT166 have anything of value to add re. matters of Science? Or, is that beyond his feeble capabilities?