Earth’s permafrost holds twice the amount of carbon currently present in the atmosphere, which makes the frozen regions potentially large sources of potent greenhouse gases under projected planetary warming. As organic carbon thaws, microbes convert these formerly frozen carbon stores into inorganic forms that can enter the atmosphere as methane and carbon dioxide.
Although previous studies have suggested that the decomposition of organic matter in Arctic soils is controlled primarily by soil moisture and temperature, this research has focused on processes specific to individual sites. The regional effects of these parameters are still poorly constrained, and the response of the terrestrial carbon cycle to a warming climate remains one of the greatest sources of uncertainty in global climate change models.
To deepen our understanding of soil organic carbon decomposition across the Arctic, Faucherre et al. analyzed differences in long-term carbon losses in samples collected from 101 locations in Svalbard, Norway; Abisko, Sweden; and Russia’s Lena Delta regions. The team assessed carbon content throughout a yearlong laboratory incubation experiment and correlated the observed losses with other parameters, including soil depth, nitrogen and water contents, and dry bulk density, an indicator of soil compaction.
The team found that samples from the uppermost active layer exhibited the highest carbon losses and that these reductions correlated most closely with dry bulk density, suggesting that this parameter may be used to predict active layer losses across the Arctic. Carbon losses from permafrost samples, by contrast, appear to be more complex and at least partially controlled by local processes, although the data indicate that the ratio of carbon to nitrogen may forecast the initial losses observed at the beginning of the experiment.
By identifying common parameters that can be used to extrapolate rates of carbon dioxide production from the local to the regional scale, this study makes an important contribution to understanding the Arctic’s complex carbon-climate feedbacks. The finding that carbon loss may not depend wholly upon site-specific factors is likely to play an important role in parameterizing, and ultimately improving, global climate change models. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1002/2017JG004069, 2018)
—Terri Cook, Freelance Writer