Alaska study helps quantify climate impacts of melting permafrost
Much of the carbon stored in ancient Alaska soils could be released to the atmosphere shortly upon melting, according to a new study that aimed to help quantify how fast permafrost decomposes and how much carbon dioxide is produced in the process.
The measurements are important because frozen organic soils are not part of the carbon cycle — but they will be as they thaw, potentially releasing huge amounts of heat-trapping gases.“Many scientists worldwide are now investigating the complicated potential end results of thawing permafrost,” said USGS scientist Rob Striegl. “There are critical questions to consider, such as: How much of the stored permafrost carbon might thaw in a future climate? Where will it go? And, what are the consequences for our climate and our aquatic ecosystems?” said Striegl, who co-authored the new research that helps answer some of the questions.
The study was done at a newly excavated tunnel operated by the U.S. Army Corps of Engineers near Fairbanks, Alaska, where a research team from USGS, the University of Colorado Boulder, and Florida State University took a close look at “yedoma” soils.
Yedoma is a distinct type of permafrost soil found across Alaska and Siberia that accounts for a significant portion of the permafrost soil carbon pool. These soils were deposited as wind-blown silts in the late Pleistocene age and froze soon after they were formed.
“It had previously been assumed that permafrost soil carbon this old was already degraded and not susceptible to rapid decomposition upon thaw,” said Kim Wickland, the USGS scientist who led the team.
The researchers found that more than half of the dissolved organic carbon in yedoma permafrost was decomposed within one week after thawing. About 50 percent of that carbon was converted to carbon dioxide, while the rest likely became microbial biomass.
“What this study adds is that we show what makes permafrost so biodegradable,” said Travis Drake, the lead author of the research. “Immediately upon thaw, microbes start using the carbon and then it is sent back into the atmosphere.” Drake was both a USGS employee and a master’s degree student at the University of Colorado during the investigation.
These rates are among the fastest permafrost decomposition rates that have been documented, showing how a permafrost meltdown could quickly ramp up levels of heat-trapping greenhouse gases in the atmosphere.
An important implication of the study for aquatic ecosystems is that dissolved organic carbon released by thawing yedoma permafrost will be quickly converted to carbon dioxide and emitted to the atmosphere from soils or small streams before it can be transported to major rivers or coastal regions.
This research was recently published in the Proceedings of the National Academy of Sciences. The National Science Foundation’s Division of Polar Programs provided essential support for the investigation.