Source: Journal of Geophysical Research: Biogeosciences
As rising temperatures across the Arctic thaw increasingly larger areas of permafrost, more and more organic carbon stored within these frozen soils is being released. Because microbes can convert this liberated material into greenhouse gases that further accelerate the warming, its fate is of grave concern.
Despite general agreement that the warming climate is amplifying the carbon cycle in northern high-latitude watersheds, the amount of permafrost thawing into Arctic rivers is poorly constrained because of the lack of a reliable tracer. To help address this gap, Rogers et al. use a novel approach to search for old permafrost-derived carbon in Russia’s Kolyma River, whose 650,000-square-kilometer watershed is completely underlain by frozen soils.
The authors employed two independent techniques to chemically fingerprint thawed permafrost carbon and track it within the Kolyma watershed during late summer, when the most permafrost thaws. The results from both techniques point to the same conclusion: Relatively little old organic carbon is derived from thawing permafrost in the Kolyma River, which is dominated by modern inputs. Importantly, the team’s analyses indicate this conclusion is true for both microbially unaltered and microbially degraded permafrost carbon.
Using a mixing model to further constrain their results, Rogers and colleagues estimated that a maximum of just 0.8% to 7.7% of the river’s late summer dissolved organic carbon comes from undegraded permafrost. This amount translates to about 6% of the 0.82 teragram of the load the Kolyma delivers to the ocean each year.
This conclusion suggests that despite increased thawing, large northern high-latitude rivers are currently transporting only minor amounts of permafrost-derived dissolved organic carbon to the Arctic Ocean. These findings have important implications for understanding the evolution of dissolved organic carbon during permafrost thaw and river transport. More knowledge of where this thawed carbon resides and how it’s affecting the Arctic’s changing carbon cycle is necessary to improve assessments of the region’s potential to accelerate global warming. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1029/2020JG005977, 2021)
—Terri Cook, Science Writer
Cook, T. (2021), Minimal evidence of permafrost carbon in Siberia’s Kolyma River, Eos, 102, https://doi.org/10.1029/2021EO163244. Published on 20 September 2021.
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