How Much Carbon Will Peatlands Lose as Permafrost Thaws?

New model for carbon balance
[07. June 2021] 

A process-based model reveals that how much carbon peatlands may lose—or accumulate—in the future varies from place to place.

Just as your freezer keeps food from going bad, so arctic permafrost protects frozen organic material from decay. As the climate warms, however, previously frozen landscapes such as peatlands are beginning to thaw. Just how much fresh carbon will be released into the atmosphere when peat leaves the deep freeze of permafrost? Scientists want to find out.

In a new study, Claire Treat (permafrost researcher at the Alfred Wegener Institute, Helmmholtz Centre for Polar and Marine Research) and colleagues use a process-based model to explore how different factors may affect the carbon balance in peatlands by the end of this century. The scientists simulated more than 8,000 years of peatland history to ensure accuracy, and they examined six peatland sites in Canada to cover a gradient from spottier southern permafrost zones to continuous permafrost sites above the arctic treeline.

Their results reveal great variation, depending on each site’s history. According to the simulations, some areas will release carbon as permafrost thaws or disappears altogether. Others will accumulate and store carbon at greater rates as vegetation responds to warmer temperatures and longer growing seasons. Overall, little carbon will escape—less than 5 percent—compared to how much will remain stored.

Before peat is preserved stably in permafrost, it spends time in an “active layer,” which freezes and thaws seasonally. Unfrozen peat continues to decay, so by the time it is permanently frozen, peat might be highly degraded. When such frozen peat ultimately thaws, little further decomposition is possible, and so less carbon is lost than might be expected.

This means that most of the carbon that peat will release escapes before it ever enters the permafrost. Accordingly, in simulations of future years, the upper active layer continued to release the most carbon—not deeper or newly thawed peat.

Previous studies disagreed about whether peat will release or store more carbon as permafrost thaws. This simulation helps explain that variation, linking carbon-balance results to specific variables such as site history and active layer depth. Future models could continue to refine our picture of the future by incorporating new variables, such as ice melt and vegetation productivity. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1029/2020JG005872, 2021)

Author: Elizabeth Thompson, Science Writer. This story was originally published on eos.org.

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