Lengthening of biogeochemical processes during winter in degraded permafrost soils

The consequences of permafrost thaw for organic carbon release are mainly studied in summer, considering the frozen soil is inert in winter. Here, we show that biogeochemical processes also occur during early winter. We combine Si isotopes and Ge/Si with Fe and dissolved organic carbon (DOC) concentrations in soil porewater along a natural gradient of permafrost degradation (palsa, intermediate and degraded palsa sites) and in river water (Stordalen, Sweden) collected during late autumn and early winter. The data support: (i) the occurrence of early winter snowmelt water infiltration in soils diluting more extensively the soil porewater in dry well-drained palsa soils; (ii) the decrease of the redox potential (by 30 %) induced by snowmelt water infiltration and water table rise at the intermediate site, favouring Fe-oxides dissolution and the release of the associated DOC in soil porewater; (iii) the contribution of snowmelt water infiltration to the Fe and DOC lateral export from permafrost degrading soils to rivers.