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.