Monday, December 14, 2020

Permafrost Carbon Changing To CO2 ? How New Experiments Shed Light On The Process


TOP:  On our dog sled trek near Fairbanks, AK (March, 2005) .  We had to choose a path where the ice hadn't melted excessively..
Bottom: Janice on her snowmobile near the Trans--Alaska pipeline.  Melting permafrost had affected its stability

In March last year, I cited a ground-breaking paper in the journal Nature Geoscience, by Natalie Shakhova and Igor Semiletov of the University of Alaska- Fairbanks' International Arctic Research Center (IARC).  In the paper the authors warned that the Arctic Ocean is releasing methane at a rate more than twice what existing scientific models predicted. The two UAF researchers focused on the continental shelf off the northern coast of eastern Russia - the East Siberian Arctic Shelf. Underlying this region is sub -sea permafrost. When the permafrost melts, the methane (CH4 )  is  released.  In a (2017) update of their earlier (2013) permafrost research, e.g.

Current rates and mechanisms of subsea permafrost degradation in ...

The authors actually showed the rate and mechanisms of subsea permafrost degradation and that it can be a meaningful prerequisite for near future predictions of methane release in the Arctic. Ice-wedge degradation has been observed before, but this is the first study to determine that rapid melting of ground ice  (as opposed to sub-sea permafrost) has become widespread throughout the Arctic.   

Permafrost has been frozen for far longer than humans have been on the planet. That’s a good thing because permafrost contains over a trillion metric tons of organic carbon deposited by generations of plants, and all that carbon remains locked up so long as it’s frozen. This is especially critical now as we have learned the Arctic is warming at twice the rate of the continental U.S.  However, while the focus of melting permafrost models has been on methane (CH4) release, the other matter of CO2 from melting permafrost has not been at the forefront- at least until now.    According to  Collin P. Ward, an aquatic geochemist at the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts:

“Now, because of human activity, it’s starting to thaw.  The big concern here is what’s going to happen to all of that organic carbon.”

The effects of thawing extend beyond climate change since buildings and roads in the Arctic are also apt to collapse when the underlying permafrost thaws.  This is what we beheld in Fairbanks in 2005, when a 150' high ice tower collapsed at an Arctic Ice Art Festival.

One way in which permafrost carbon gets converted to carbon dioxide is via microbes—or  microscopic life-forms.  Think of them  (several trillion) chowing down on carbon and respiring carbon dioxide.  It would not be an insignificant amount of CO2 released in this process.

True,  this microbial process is generally taken into account in climate models, but comparably little is known about the permafrost carbon that’s flushed into lakes and rivers, where it’s exposed to sunlight.   Collin Ward again, quoted in a recent issue of EOS Space Science;

 “We’ve known for a while that sunlight converts organic carbon to carbon dioxide, but the governing control of this process has escaped us,” 

It’s been hypothesized that this photo-mineralization might be controlled by the presence of iron,  abundant in Arctic fresh waters.   Ward again: 

There have been lots of lab-based studies suggesting that iron is a key player, but this is the first to let nature tell us what controls this process,” 

Ward and his colleagues have calculated that the highest rates of photo-mineralization occur in the presence of visible light.  Hence, the process dominates in nature.  Two factors contribute to this: first, Earth’s surface receives significantly more visible light than ultraviolet light.  Second, iron kick-starts reactions at longer wavelengths, the team showed. (Visible light is characterized by longer wavelengths than ultraviolet light.)

Photo-mineralization’s wavelength dependence has important implications, according to Ward. It means that permafrost carbon in deep lakes or rivers is still apt to be converted to carbon dioxide.   In his words:

As you move deeper into the water column, there’s less ultraviolet light available and more visible light,”

The researchers further determined that the older carbon found in permafrost—several thousand years old—was roughly twice as effective at producing carbon dioxide as modern carbon. Modern carbon has more sunlight-absorbing compounds, said team member Jenny Bowen, a biogeochemist at the University of Michigan, but permafrost carbon is better at reaping the reaction-promoting benefits of iron.

This unaccounted-for contribution (from older carbon) has the potential to fundamentally change the carbon cycle, according to Ted Schuur, an ecosystem ecologist at Northern Arizona University in Flagstaff not involved in the Ward et al research.  In Schuur's words:

 “Stuff that wasn’t part of the atmosphere is suddenly ending up in the atmosphere.”

Since photo-mineralization of permafrost carbon isn’t presently included in climate models, estimates of future global warming are lowballed, the researchers concluded. In the words of Jenny Bowen:

 “Sunlight increases the amount of carbon dioxide coming from thawing permafrost by 14%.  The planet will warm even more than expected.”

These results were published last month in Geophysical Research Letters.

The obvious next step for the research teams is to study how microbial degradation works in tandem with sunlight and photo-mineralization to facilitate the transformation of carbon to CO2.  We especially would like to know the rate at which this occurs now and the projected rate as more permafrost melts, say by 2037. That date is when the most pronounced greenhouse warming effects are forecast to begin.

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by Elizabeth Cerceo | December 14, 2020 - 6:52am | permalink

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