Ancient permafrost quickly transforms to carbon dioxide upon thaw

http://www.eurekalert.org/pub_releases/2015-10/uoca-apq102615.php

Public Release: 26-Oct-2015
Ancient permafrost quickly transforms to carbon dioxide upon thaw
University of Colorado at Boulder

Researchers from the U.S. Geological Survey and key academic partners including the University of Colorado Boulder have quantified how rapidly ancient permafrost decomposes upon thawing and how much carbon dioxide is produced in the process.

Huge stores of organic carbon in permafrost soils -- frozen for hundreds to tens of thousands of years across high northern latitudes worldwide -- are currently isolated from the modern day carbon cycle. However, if thawed by changing climate conditions, wildfire, or other disturbances, this massive carbon reservoir could decompose and be emitted as the greenhouse gases carbon dioxide and methane, or be carried as dissolved organic carbon to streams and rivers.

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At a newly excavated tunnel operated by the U.S. Army Corps of Engineers near Fairbanks, Alaska, a research team from USGS, CU-Boulder and and Florida State University set out to determine how rapidly the dissolved organic carbon from ancient (about 35,000 years old) "yedoma" soils decomposes upon soil thaw and how much carbon dioxide is produced.

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"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."

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The researchers attribute this rapid decomposition to high concentrations of low molecular weight organic acids in the dissolved organic carbon, which are known to be easily degradable and are not usually present at high concentrations in other soils.

These rates are among the fastest permafrost decomposition rates that have been documented. It is the first study to link rapid microbial consumption of ancient permafrost soil-derived dissolved organic carbon to the production of carbon dioxide.

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