A team of researchers lead by Florida State University have found new evidence that permafrost thawing is releasing large quantities of greenhouse gases into the atmosphere via plants, which could accelerate warming trends.
The research is featured in the newest edition of the Proceedings of the National Academy of Sciences.
“We’ve known for a while now that permafrost is thawing,” said Suzanne Hodgkins, the lead author on the paper and a doctoral student in chemical oceanography at Florida State. “But what we’ve found is that the associated changes in plant community composition in the polar regions could lead to way more carbon being released into the atmosphere as methane.”
Permafrost is soil that is frozen year round and is typically located in polar regions. As the world has gotten slightly warmer, that permafrost is thawing and decomposing, which is producing increased amounts of methane.
Relative to carbon dioxide, methane has a disproportionately large global warming potential. Methane is 33 times more effective at warming the Earth on a mass basis and a century time scale relative to carbon dioxide.
As the plants break down, they are releasing carbon into the atmosphere. And if the permafrost melts entirely, there would be five times the amount of carbon in the atmosphere than there is now, said Jeff Chanton, the John Widmer Winchester Professor of Oceanography at Florida State.
“The world is getting warmer, and the additional release of gas would only add to our problems,” he said.
Chanton and Hodgkins’ work, “Changes in peat chemistry associated with permafrost thaw increase greenhouse gas production,” was funded by a three-year, $400,000 Department of Energy grant. They traveled to Sweden multiple times to collect soil samples for the study.
The research is a multicontinent effort with researchers from North America, Europe and Australia all contributing to the work.
We address the effect of thawing permafrost, and attendant subsidence-induced shifts in hydrology and plant community structure, on CH4 and CO2 production potentials and mechanisms driven by changes in organic matter chemical composition in a thawing peatland complex.
Advanced analytical characterization of peat and dissolved organic matter along the thaw progression indicated increasingly reduced organic matter experiencing greater humification rates, which were associated with higher relative CH4 and CO2 production potentials, increasing relative CH4/CO2 production ratios, and shifts from hydrogenotrophic to acetoclastic methanogenesis.
The effects of this increase in organic matter reactivity with permafrost thaw could intensify the increases in CH4 and CO2 release already predicted due to increasing temperatures, permafrost carbon mobilization, and waterlogging-induced changes in redox conditions.
Carbon release due to permafrost thaw represents a potentially major positive climate change feedback. The magnitude of carbon loss and the proportion lost as methane (CH4) vs. carbon dioxide (CO2) depend on factors including temperature, mobilization of previously frozen carbon, hydrology, and changes in organic matter chemistry associated with environmental responses to thaw. While the first three of these effects are relatively well understood, the effect of organic matter chemistry remains largely unstudied.
To address this gap, we examined the biogeochemistry of peat and dissolved organic matter (DOM) along a ∼40-y permafrost thaw progression from recently- to fully thawed sites in Stordalen Mire (68.35°N, 19.05°E), a thawing peat plateau in northern Sweden. Thaw-induced subsidence and the resulting inundation along this progression led to succession in vegetation types accompanied by an evolution in organic matter chemistry.
Peat C/N ratios decreased whereas humification rates increased, and DOM shifted toward lower molecular weight compounds with lower aromaticity, lower organic oxygen content, and more abundant microbially produced compounds. Corresponding changes in decomposition along this gradient included increasing CH4 and CO2 production potentials, higher relative CH4/CO2 ratios, and a shift in CH4 production pathway from CO2 reduction to acetate cleavage.
These results imply that subsidence and thermokarst-associated increases in organic matter lability cause shifts in biogeochemical processes toward faster decomposition with an increasing proportion of carbon released as CH4. This impact of permafrost thaw on organic matter chemistry could intensify the predicted climate feedbacks of increasing temperatures, permafrost carbon mobilization, and hydrologic changes.