Organic carbon accumulation in post-glaciated catchments in northern latitudes

Glacier retreat in northern latitudes exposes nutrient-rich glacial landscapes that may develop soils and ecosystems. Future soil development following glacier retreat might lead to carbon sequestration creating negative climate feedback. Soil development was characterised in three contrasting glacial systems (Tarfala in Sweden, Vatnajokull ice cap in Iceland and Zackenberg in Greenland) to understand the main source of organic carbon (OC) in soils, as well as soil development along transects away from the glacier front. Soil samples were analysed for OC concentration, bacteriohopanepolyol biomarkers (BHPs, a group of membrane lipids that can be used to trace major microbial groups) and DNA sequencing of microbes.Soil and sediment samples from Sweden showed low OC concentrations (0.27%), while samples from Iceland (1.59%) and Greenland (1.62%) had higher values, indicative of OC accumulation in the latter catchments. Soils from older moraines showed the highest OC concentrations (up to 8.96% in Greenland), while samples from more recently deglaciated areas in Sweden had low OC. BHPs were detected in most soil samples with the exception of samples with low OC content in Sweden. Higher fractional abundance of soil-specific BHPs (up to 30% in Greenland) away from glacier fronts, and matching increases in the soil index (up to 0.37 in Greenland), suggest soils are gradually developing in recently deglaciated areas, along with a stable soil microbial community being observed in older soils in Iceland and Greenland.Microbial communities stabilized along transects, quickly adapting to the new environment. Acidobacteria, Actinobacteria, Chloroflexi, Proteobacteria, Planctomycetes and Verrucomicrobia were the most abundant phyla identified in post-glaciated terrains, while candidate phylum AD3 had surprisingly high concentrations in samples from Sweden. Linking organic biomarkers with bacterial community suggests that soil-marker BHPs may have been produced by Rhodospirillaceae (Proteobacteria) in Sweden and Bradyrhizobiaceae (Proteobacteria) in Iceland and Greenland.