A study of 96
watersheds in western Siberia is showing an alarming trend: If temperatures
in the region and throughout the Arctic continue to rise, by the end of this
century, land surface that is covered by permafrost will be halved — leaching
carbon into the area’s water system. Considering that vegetation throughout
West Siberia contains one-third of the carbon buried in the world’s soils,
such a permafrost loss could dramatically affect the global climate cycle.
Dissolved organic carbon produces an orange
color in water in West Siberia. New research is showing that as temperatures
rise across the Arctic, carbon once locked up in permafrost soils may begin
escaping into the area’s waterways. Courtesy of Karen Frey.
Most studies of the effects of melting Arctic permafrost tend to focus on direct
emissions to the atmosphere of carbon dioxide and methane from the peat —
compacted undecomposed plant matter — newly exposed beneath the melting
permafrost. But, says Karen Frey, a hydrologist at the University of California,
Los Angeles (UCLA), streams and rivers could also lead to atmospheric carbon
dioxide emissions by carrying once-buried carbon out of the peat and into the
ocean.
Peat up to 11 meters thick covers about 600,000 square kilometers of West Siberia
— an area encompassing 2.6 million square kilometers — some exposed
on the surface, some buried below the permafrost. Two of the world’s largest
rivers drain this region, flowing into the Arctic Ocean, which exhibits the
world’s highest flux of dissolved organic matter. Frey and her colleague
Laurence Smith, also at UCLA, measured the dissolved organic carbon fluxes throughout
streams and rivers in about 1 million square kilometers of land.
As reported in the May 5 Geophysical Research Journal, 43 of the streams
the researchers measured were in permafrost areas, while the remaining areas
were not. In permafrost-free areas, dissolved organic carbon concentrations
in the water were higher where there was more peat. Where the permafrost was
intact, however, the researchers measured very little dissolved organic carbon
whether or not there was a lot of peat. Furthermore, Frey says, they found that
on average, concentrations of carbon material in the permafrost-free areas were
more than triple that in colder areas — indicating that increasing the
amount of peat exposed in an area increases the amount of carbon released into
the region’s waterways.
“Warmer temperatures are going to happen; there’s little question
of that,” Frey says, and the warming is much more amplified in the Arctic
than elsewhere — as a whole, studies suggest that the Arctic will rise
4 to 7 degrees Celsius over the next 100 years. Currently, 55 percent of West
Siberia is perpetually frozen. “Our numbers show that, under the least
conservative scenario, 98 to 99 percent of that area will warm above the temperature
threshold” that keeps permafrost frozen, she says. Even if the warming
were less, Frey says, “that’s pretty significant.”
Dissolved organic carbon leaches out of peat and is dumped into the Arctic Ocean,
where bacteria decompose the carbon material over a decade. The carbon is then
released as carbon dioxide into the atmosphere, thus providing yet another positive
feedback system: As Earth warms, dissolving and decomposing peat releases more
carbon into the atmosphere, thus warming Earth more, says Robert Holmes of the
Woods Hole Research Center in Massachusetts. Just how much carbon dioxide could
be released into the atmosphere from the decomposition of dissolved organic
carbon from peat is a significant question, he says.
Although Frey says that direct carbon dioxide and methane emissions from the
melting permafrost will be more significant, the amount of carbon released into
the water from peat decomposition is still something that needs to be considered
in climate models and carbon cycles.
Frey and Smith’s projections of dissolved organic carbon flux based on
temperature increases are “significant and reasonable,” Holmes says.
Researchers now need to figure out if the entire Arctic will behave this way,
he says, and by how much the temperature will actually change over the next
century.
Megan Sever
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