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Alaska Soil Research Project Aiming to Improve Understanding of Global Climate

November 26, 2012

A research team being led by Julie Jastrow, an ecologist at the U.S. Department of Energy's (DOE) Argonne National Laboratory, recently traveled to the North Slope of Alaska as part of a soil research project that aims to ultimately help improve and validate global climate models.

Using jackhammer to dig a sampling pit in frozen soil
After removing the seasonally thawed soil active layer in coastal plain tundra near Prudhoe Bay, members of the Argonne research team use a jackhammer to dig through frozen soil, creating a soil pit from which different soil layers can be viewed and sampled.

A significant source of greenhouse gases is leaking into the Earth's atmosphere from an unlikely place. Above the Arctic Circle, land frozen for tens of thousands of years has started to thaw for the first time. Current estimates indicate that perennially frozen ground, called permafrost, holds more than twice the amount of carbon present in today's atmosphere. As permafrost thaws, a huge amount of this stored carbon could be released as carbon dioxide or methane gas.

In more temperate environments, most of the carbon in dead plant material cycles relatively quickly back to the atmosphere thanks to the action of microbes that break down organic materials. However, the remains of dead plants have accumulated for millennia in the permafrost layers of soils and sediments in regions like the North Slope of Alaska and Siberia.

"Once organic material gets incorporated into permafrost, it's pretty much out of the system. It's like keeping food in the freezer—the rate of decomposition is dramatically slowed," said Jastrow.

"As long as the soil or sediment stays frozen, there's very little microbial action to decompose the organic matter," Jastrow added. "Once the soil does start to thaw, though, microbial activity will increase, and as the microbes feed on the organic materials, some of the carbon will be released to the atmosphere. The concern is that this added source of greenhouse gases would then speed up the warming process, leading to even greater thawing of more permafrost."

The freeze-thaw cycles associated with Arctic tundra produce a phenomenon known as cryoturbation, in which the top layers of soil churn together with lower layers. According to Jastrow, for thousands of years this process has transported dead plant materials downward through the sediment into the permafrost before they were significantly decomposed.

"The issue is that there's lots of relatively easy-to-decompose carbon that's buried down there, but it's protected by being in a frozen state. If it thaws and the microbes act on it, then—just like the burning of fossil fuels— it’s going to release carbon that has been out of the global cycle for a long time, and it really can't be easily put back where it came from. What we don't know yet is how much of this ancient carbon will be released, how fast, and in which form — carbon dioxide or methane." Jastrow said.

Soil pit in coastal plain tundra with exposed ice wedge
Completed soil pit after sampling. Small circular holes to left of tape are locations where soil samples were collected by coring into the pit face. The white area in the lower right corner of the pit is the top of a massive ice wedge, which is a typical ice feature of the coastal plain tundra and forms over thousands of years as a result of repeated freeze-thaw cycles.

For researchers and policymakers concerned about climate change, one particularly troubling aspect of permafrost thaw lies in the fact that these soils and sediments typically contain a large amount of ice. If water from thawing ice drains away, carbon emissions will be mostly carbon dioxide. But in poorly drained areas, water ponds up and a significant amount of methane can be emitted. When carbon is released as methane, it will generate 25 times the warming effect over a century that would be produced by its release as carbon dioxide.

A team of 10 researchers, including Jastrow, fellow ecologists Roser Matamala and Mike Miller plus biogeochemical modeler Zhaosheng Fan from Argonne, soil scientists Chien-Lu Ping and Gary Michaelson from the University of Alaska Fairbanks, three technical assistants, and a graduate student, recently collected samples of tundra soils from the North Slope of Alaska between the Brooks Range and Prudhoe Bay.

Some of the collected samples will be used in laboratory studies to closely examine the chemical forms of carbon and minerals stored in permafrost soils and to observe the behavior of microbes feeding on the carbon as these soils are slowly warmed under different drainage conditions. From these studies, the researchers plan to develop decomposability indicators and predictive models that can be used to better anticipate the fate of carbon in thawing permafrost.

Other soil samples will be carefully quantified to characterize the spatial distribution of carbon in relation to the depth of permafrost and landscape features. With the help of another Argonne research team member, Umakant Mishra, a geospatial modeler, these data will be used to develop high-resolution, three-dimensional maps of the carbon stored in permafrost region soils. According to Jastrow, such maps will greatly reduce current uncertainties. "Our mandate is to look into both the quantity of carbon as well as its potential decomposability. Permafrost researchers now believe that there's significantly more carbon in these regions than most people previously thought, but we still only have very crude estimates," she said.

Ultimately, the Argonne efforts will support DOE's goal of developing climate models that can better predict impacts to different biomes. Understanding the long-term behaviors of terrestrial ecosystems requires a more comprehensive picture of the different factors controlling how carbon cycles between the land and the atmosphere in different regions. "We're frequently faced with the question of whether our measurements are off or our models are off, and typically it's some of both," Jastrow said.

The Argonne studies will provide valuable "ground truthing" data needed to test and improve carbon cycle models being developed for the northern permafrost region, which includes shrubland, boreal forest, and peatland below the Arctic Circle, in addition to tundra. Future research will involve iterative sampling of more sites to address data gaps identified by the carbon mapping work, as the DOE continues its effort to couple carbon models with climate models.


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