Microbes Quickly Convert Thawing Yedoma Permafrost to Carbon Dioxide

Summary: A study in Oct. 26's Proceedings of the National Academy of Sciences finds microbes quickly convert thawing Yedoma permafrost soils to carbon dioxide.

melting Yedoma permafrost formation, with large ice wedges, along Itkillik River, northern Alaska: Mikhail Kanevskiy/University of Alaska Fairbanks Institute of Northern Engineering, no usage restrictions, via EurekAlert!

Microbes rapidly convert carbon in Alaska’s thawing Yedoma permafrost soils to carbon dioxide for release into the air as greenhouse gases and for entry into water pathways, according to a study published Oct. 26, 2015, in the Proceedings of the National Academy of Sciences.

The five authors present their study as the first to make direct links between microbial uptake of ancient permafrost-derived dissolved organic carbon (DOC), high concentrations of low-molecular-weight (LMW) organic acid, high biodegradability of permafrost’s dissolved organic carbon, and rapid production of carbon dioxide. Findings suggest that permafrost’s aged organic carbon (OC), separated from the modern carbon cycle since the Late Pleistocene (126,000 to 11,800 years ago), is highly biodegradable and promptly converts after thawing, through decomposition of low-molecular-weight (LMW) organic acids, to carbon dioxide.

The rapid turnover from ancient dissolved organic carbon causes the majority of carbon dioxide to be emitted quickly, close to soil porewaters, as a greenhouse gas into the atmosphere. Rapid release high in the watershed, near thawing sites, accounts for the absence of Yedoma dissolved organic carbon downstream in major Arctic rivers and creates a blind spot in assessments of dissolved organic carbon percentages in inland Arctic waters. The study suggests that by 2100 thawing Yedoma permafrost in Alaska and Siberia may amount to 19 to 26 percent of all Arctic river-exported DOC.

The authors note in their abstract: “The observed DOC loss rates are among the highest reported for permafrost carbon and demonstrate the potential importance of LMW DOC in driving the rapid metabolism of Pleistocene-age permafrost carbon upon thaw and the outgassing of CO2 to the atmosphere by soils and nearby inland waters.”

Soil samples come from the newly excavated extension of the U.S. Army Corps of Engineers’ Fox Permafrost Tunnel north of Fairbanks. Experiments take place in a gas-tight, stainless steel bioreactor that allows for simultaneously identifying changes in the DOC pool and tracking conversion to carbon dioxide. The experiment’s five incubations are undertaken at a setting of 20 degrees Celsius, the maximum summer temperature in Arctic water ecosystems.

Leached from permafrost soil with a radiocarbon age of 35,800 years Before Present (BP), DOC concentrations average a rapid, 53 percent decrease within 100 hours of thawing while dissolved inorganic carbon (DIC), as carbon dioxide, shows a sevenfold increase in concentration. Complete microbial decomposition of two low-molecular-weight organic acids, acetate and butyrate, accounts for 87 percent of the DOC loss.

As a vast source of rapid greenhouse gas emissions, thawing Yedoma permafrost could drive the process of permafrost climate feedback, a cycle of continued global warming and accelerated permafrost thaw. A significant portion of the carbon reservoir stored in northern permafrost soils, which equals nearly twice the amount in the atmosphere, occurs in Yedoma permafrost soils. Yedoma features an ice- and carbon-rich soil formed by syngenetic (i.e., frozen at time of deposit), windblown silt deposits across modern-day Alaska, northwestern Canada and Siberia during the Late Pleistocene.

inside view of U.S. Army's CRREL (Cold Regions Research and Engineering Laboratory); samples for study by Travis Drake et al. were collected in the geologic time tunnel known as the Permafrost Tunnel: Travis Drake, no usage restrictions, via EurekAlert!

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

thawing Yedoma permafrost formation: Mikhail Kanevskiy/University of Alaska Fairbanks Institute of Northern Engineering, no usage restrictions, via EurekAlert! @ http://www.eurekalert.org/multimedia/pub/102024.php?from=310012

inside view of permafrost tunnel: Travis Drake, no usage restrictions, via EurekAlert! @ http://www.eurekalert.org/multimedia/pub/102021.php?from=310007

For further information:

Drake, Travis W., et al. "Ancient low-molecular-weight organic acids in permafrost fuel rapid carbon dioxide production upon thaw." Proceedings of the National Academy of Sciences of the United States of America, vol. 112, no. 145 (Nov. 10, 2015): 13946-13951. Published online before print Oct. 26, 2015. DOI: 10.1073/pnas.1511705112
Available @ http://www.pnas.org/content/early/2015/10/21/1511705112.full.pdf

"Pools, Fluxes and a Word About Units." University of New Hampshire GLOBE Carbon Cycle.
Available @ http://globecarboncycle.unh.edu/CarbonPoolsFluxes.shtml

Roger Highfield @RogerHighfield. "Permafrost soil from an Alaskan tunnel provide new clues to understand what happens as northern regions thaw." Twitter. Oct. 27, 2015.
Available @ https://twitter.com/RogerHighfield/status/659256673236832256

USGS News Release. "Study shows thawing quickly turns into CO2, a climate concern." University of Colorado Boulder News Center. Oct. 26, 2015.
Available @ http://www.colorado.edu/news/releases/2015/10/26/study-shows-thawing-permafrost-quickly-turns-co2-climate-concern