This week, in an article published as a Correspondence in Nature Geoscience, scientists from Stockholm University and Utrecht University highlight the need to broaden our perspective on the climate feedback potential of thawing Arctic permafrost. They particularly stress the role of the interplay between large-scale carbon- and water cycles in the Arctic permafrost carbon feedback. 

Arctic permafrost has often been coined as the “sleeping giant” of climate change. Globally, about half of all soil carbon is stored in permafrost. This is twice as much as is currently stored as CO2 and other greenhouse gases in the atmosphere. As warming causes permafrost to thaw, respiration of organic matter in it will release carbon to the atmosphere, potentially leading to a positive feedback. The general consensus on Arctic permafrost carbon feedback is that it can facilitate the release of some 10-500 billion tons of carbon, which, if all were converted to CO2, would bring about an increase in atmospheric CO2 between 1 and 60 percent.
However, as they point out in Nature Geoscience, Örjan Gustafsson, Professor at Stockholm University, and Jorien Vonk, former PhD student at Stockholm University now at Utrecht University, Netherlands, find that these estimates rest on numerous one-dimensional and overly simplistic assumptions. “These scenarios are based on the notion that carbon is only released from the top layer of permafrost that thaws and freezes every year whilst they don’t take into account abrupt release through fire and erosion”, says Örjan Gustafsson.
Örjan Gustafsson, Professor of Biogeochemistry at ITM
Örjan Gustafsson, Professor of Biogeochemistry. Photo: Stella Papadopoulou

Also, according to the authors, these estimates typically assume a complete conversion of Arctic permafrost carbon to CO2 and methane within a few hundreds years, and only at the thaw site. Instead, Örjan Gustafsson and Jorien Vonk propose that horizontal transport of thawed Arctic permafrost carbon through streams, lakes, rivers and the coastal ocean will result in greenhouse gas release hundreds to thousands of kilometres away from the thaw site. “A portion of the thawed and remobilized Arctic permafrost carbon may also be re-buried in lake and ocean bottoms, thus decreasing the expected release of greenhouse gases to the atmosphere,” explains Jorien Vonk.

Clues from Russian-Arctic rivers
Örjan Gustafsson and Jorien Vonk’s hypothesis of the water-borne distribution of thawed Arctic permafrost carbon scenario outlined in Nature Geoscience finds support in the findings of a recent study they co-authored together with colleagues from Switzerland, Russia and UK. There, they showed that water-borne mobilization of ancient Arctic permafrost carbon has increased across the entire Eurasian Arctic. The study was published on 12 August as an Early Edition in Proceedings of the National Academy of Sciences USA.

The research team employed a novel technique that can isolate source-specific organic molecules to examine the carbon-14 signature of various carbon pools from the huge drainage basins to the mouths of the great Russian-Arctic rivers. In doing so, the team found differences of up to 13,000 years in age offsets between two groups of the most commonly-used markers to trace land-carbon, namely lignin and plant wax lipids. “This observation stands in sharp contrast with the conventional assumption that land-derived carbon has similar age or residence time before deposition into the sedimentary environment,” says Örjan Gustafsson.

The scientists found that the ages of these terrestrial markers are related to the river water runoff and geographic characteristics across the watersheds. As such, the age of young carbon from surface sources (traced by lignin) decreases with increasing river runoff rate whereas ancient (permafrost) carbon (traced by plant wax lipids) becomes older in discontinuous permafrost regions. “These continental-scale correlations are fascinating, as they provide novel insights into the contrasting mobilization mechanisms of surface versus deep (permafrost) carbon pools in the Arctic, ” says Örjan Gustafsson.

Örjan Gustafsson and Jorien Vonk are convinced that unravelling the array of different delivery pathways of Arctic carbon pools could provide insightful clues as to the mechanisms and even future trends of Arctic permafrost carbon release. “While there is no doubt that thawing of permafrost carbon in the Arctic is a major consequence of a warming climate, there is an urgent need to better understand how this system responds in order to predict the magnitude of the reinforcing effect of Arctic permafrost carbon on global warming,” says Örjan Gustafsson.

More information:
Örjan Gustafsson, Professor of Biogeochemistry, Stockholm University tfn 0703-24 73 17,
Jorien E. Vonk, Department of Earth Sciences, Utrecht University, tfn +31(0)611-286-677, e-post