Age and chemistry of dissolved organic carbon reveal enhanced leaching of ancient labile carbon at the permafrost thaw zone
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Published:2022-02-28
Issue:4
Volume:19
Page:1211-1223
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
McFarlane Karis J.ORCID, Throckmorton Heather M., Heikoop Jeffrey M., Newman Brent D., Hedgpeth Alexandra L., Repasch Marisa N.ORCID, Guilderson Thomas P., Wilson Cathy J.ORCID
Abstract
Abstract. Climate change will alter the balance between frozen and thawed
conditions in Arctic systems. Increased temperatures will make the extensive
northern permafrost carbon stock vulnerable to decomposition and
translocation. Production, cycling, and transport of dissolved organic
carbon (DOC) are crucial processes for high-latitude ecosystem carbon loss
that result in considerable export off the Arctic landscape. To identify
where and under what conditions permafrost DOC is mobilized in an Arctic
headwater catchment, we measured radiocarbon (14C) of DOC and assessed DOC composition with ultraviolet–visible spectroscopy (UV–Vis) of surface
waters and shallow and deep subsurface porewaters from 17 drainages in the
Barrow Environmental Observatory in Alaska. Samples were collected in July
and September 2013 to assess changes in age and chemistry of DOC over time. DOC age was highly variable ranging from modern (19 ‰ Δ14C) to approximately 7000 BP (−583 ‰ Δ14C). DOC age increased with depth, over the summer as the
active layer deepened, and with increasing drainage size. DOC quality
indicators reflected a DOC source rich in high molecular-weight and aromatic
compounds, characteristics consistent with vegetation-derived organic matter
that had undergone little microbial processing, throughout the summer and a
weak relationship with DOC age. In deep porewaters, DOC age was also
correlated with several biogeochemical indicators (including dissolved
methane concentration, δ13C, and the apparent fractionation
factor), suggesting a coupling between carbon and redox biogeochemistry
influencing methane production. In the drained thawed lake basins included
in this study, DOC concentrations and contributions of vegetation-derived
organic matter declined with increasing basin age. The weak relationship
between DOC age and chemistry and consistency in DOC chemical indicators
over the summer suggest a high lability of old DOC released by thawing
permafrost.
Funder
Biological and Environmental Research
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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