Fig. 1: Microbial iron-cycling and carbon release as dissolved organic carbon (DOC), carbon dioxide and methane emissions along a palsa hillslope.

a Carbon dioxide and methane emissions along the palsa hillslope with highest emissions at the collapsing front. The reported values and error bars represent the average and standard deviation of measurements collected on three days at three separate time points in June/July 2019. b Aqueous iron (Fe²⁺) and DOC pulse along the palsa hillslope in the transition zone (interface between organic and mineral horizon, 30 cm depth) with highest values at the collapsing front. Reported values and error bars represent the average and standard deviation of eight palsa to bog hillslopes sampled in June/July 2019. Suprapermafrost water was analyzed in the deeper mineral horizons and cannot explain the pulse of aqueous Fe²⁺ and DOC at the collapsing front (Supplementary Fig. S6). c Relative 16S rRNA gene abundance of iron- and methane-cycling strains along the palsa hillslope with highest abundances at the collapsing front: I) Fe(II)-oxidizing, II) Fe(III)-reducing, III) methanogenic and IV) methanotrophic. Small letters above data mean significant differences (P < 0.05, one-way ANOVA: TukeyHSD test).