Differential mobilization of terrestrial carbon pools in Eurasian Arctic river basins

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Feng, Xiaojuan
Vonk, Jorien E.
van Dongen, Bart E.
Gustafsson, Orjan
Semiletov, Igor P.
Dudarev, Oleg V.
Wang, Zhiheng
Montlucon, Daniel B.
Wacker, Lukas
Eglinton, Timothy I.
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Fluvial mobilization
Compound-specific 14C
Hydrogeographic control
Mobilization of Arctic permafrost carbon is expected to increase with warming-induced thawing. However, this effect is challenging to assess due to the diverse processes controlling the release of various organic carbon (OC) pools from heterogeneous Arctic landscapes. Here, by radiocarbon dating various terrestrial OC components in fluvially- and coastally-integrated estuarine sediments, we present a unique framework for deconvoluting the contrasting mobilization mechanisms of surface versus deep (permafrost) carbon pools across the climosequence of the Eurasian Arctic. Vascular-plant-derived lignin phenol 14C contents reveal significant inputs of young carbon from surface sources whose delivery is dominantly controlled by river runoff. In contrast, plant wax lipids predominantly trace ancient (permafrost) OC that is preferentially mobilized from discontinuous permafrost regions where hydrological conduits penetrate deeper into soils and thermokarst erosion occurs more frequently. As river runoff has significantly increased across the Eurasian Arctic in recent decades, we estimate from an isotopic mixing model that, in tandem with an increased transfer of young surface carbon, the proportion of mobilized terrestrial OC accounted for by ancient carbon has increased by 3-6% between 1985-2004. These findings suggest that, while partly masked by surface-carbon export, climate-change-induced mobilization of old permafrost carbon is well under way in the Arctic.
Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 110 (2013): 14168–14173, doi:10.1073/pnas.1307031110.
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