Contribution of Peatland Permafrost to Dissolved Organic Matter along a Thaw Gradient in North Siberia

Permafrost peatlands are important carbon stocks currently
experiencing rapid evolution after permafrost thaw. Following thaw,
dissolved organic matter (DOM) is a potentially important pathway
for the release of permafrost carbon. This study investigates the
origin and composition of DOM across sites at different stages of
thaw in a discontinuous permafrost area of North Siberia. We determine
the optical properties, molecular composition, and stable isotopic
(δ13C) and radiocarbon (14C) contents
of DOM. Early stages of thaw are characterized by high DOC concentrations,
high aromaticity, contribution of vegetation-derived DOM, and a high
contribution of permafrost carbon. In contrast, in later stages, the
microbial contribution to DOM increases, and only modern carbon is
detected. This work links DOM composition with its radiocarbon content
in permafrost peatlands. It shows that DOM originating from previously
frozen permafrost peatlands is highly aromatic and previously processed.
It highlights the variability of post-thaw carbon dynamics in boreal
and arctic ecosystems.