Aufeis are sheets of ice unique to cold regions that originate from repeated flooding and freezing events during the winter. They have hydrological importance associated with summer flows and winter insulation, but little is known about the seasonal dynamics of the unfrozen sediment layer beneath them. This layer may support perennial groundwater flow in regions with otherwise continuous permafrost. For this study, ground penetrating radar (GPR) were collected in September 2016 (maximum thaw) and April 2017 (maximum frozen) at the Kuparuk aufeis field on the North Slope of Alaska. Supporting surface nuclear magnetic resonance data were collected during the maximum frozen campaign. These point-in-time geophysical data sets were augmented by continuous subsurface temperature data and periodic Structure-from-Motion digital elevation models collected seasonally. GPR and difference digital elevation model data showed up to 6 m of ice over the sediment surface. Below the ice, GPR and nuclear magnetic resonance identified regions of permafrost and regions of seasonally frozen sediment (i.e., the active layer) underlain by a substantial lateral talik that reached >13-m thickness. The seasonally frozen cobble layer above the talik was typically 3- to 5-m thick, with freezing apparently enabled by relatively high thermal diffusivity of the overlying ice and rock cobbles. The large talik suggests that year-round groundwater flow and coupled heat transport occurs beneath much of the feature. Highly permeable alluvial material and discrete zones of apparent groundwater upwelling indicated by geophysical and ground temperature data allows direct connection between the aufeis and the talik below.

Purpose Although many studies have paid attention to the storage and dynamics of organic carbon (OC) in the Arctic permafrost, there are limited reports for low-latitude alpine permafrost ecosystems like Qinghai-Tibet Plateau (QTP). The aims of this study are to (1) reveal the vertical distribution of OC stocks in permafrost soils; (2) assess the storage and transformation of permafrost OC; and (3) disentangle the effect of mineral protection on OC storage in permafrost soils. Materials and methods A 2-m permafrost profile on the QTP was investigated to understand vertical distribution of organic matter (OM) in different density fractions based on elemental composition, carbon stable isotope (delta C-13), mineral grain size, Fe and Al concentrations, and solid-state C-13 nuclear magnetic resonance spectroscopy (C-13 NMR). Results and discussion A positive relationship between light fraction organic carbon (LOC) and root abundance indicates that root is an important contributor for LOC. However, in heavy fractions, the total organic carbon to total nitrogen ratio (TOC/TN) is significantly lower than that in light fractions. This, combined with a negative correlation between TOC/TN and heavy fraction organic carbon (HOC), indicates that microbial input affects the quantity of HOC. In the active layer, the downward decreased delta C-13, elevated alkyl/O-alkyl, and decreased ratio of 70-75:52-57 ppm suggest selected decomposition of carbohydrate components. While in the deep permafrost layer, the relatively constant delta C-13 values and chemical composition of OM suggest a stable environment and minor impact of cryoturbation. The redundancy analysis shows that soil textures and concentration of Fe and Al have weak correlations with OC content, but for deep permafrost soils only, fine soil fraction is associated with aromatic carbon, and Al has strong influence on alkyl carbon, which could be attributed to OM-mineral stabilization. Conclusions Our results suggest that soil textures and Fe and Al concentration affect SOM preservation in the permafrost soils on the QTP; however, they largely control the quality rather than quantity of OM.

With increased warming in the Arctic, permafrost thaw may induce localized physical disturbance of slopes. These disturbances, referred to as active layer detachments (ALDs), redistribute soil across the landscape, potentially releasing previously unavailable carbon (C). In 2007-2008, widespread ALD activity was reported at the Cape Bounty Arctic Watershed Observatory in Nunavut, Canada. Our study investigated organic matter (OM) composition in soil profiles from ALD-impacted and undisturbed areas. Solid-state C-13 nuclear magnetic resonance (NMR) and solvent-extractable biomarkers were used to characterize soil OM. Throughout the disturbed upslope profile, where surface soils and vegetation had been removed, NMR revealed low O-alkyl C content and biomarker analysis revealed low concentrations of solvent-extractable compounds suggesting enhanced erosion of labile-rich OM by the ALD. In the disturbed downslope region, vegetation remained intact but displaced material from upslope produced lateral compression ridges at the surface. High O-alkyl content in the surface horizon was consistent with enrichment of carbohydrates and peptides, but low concentrations of labile biomarkers (i.e., sugars) suggested the presence of relatively unaltered labile-rich OM. Decreased O-alkyl content and biomarker concentrations below the surface contrasted with the undisturbed profile and may indicate the loss of well-established pre-ALD surface drainage with compression ridge formation. However, pre-ALD profile composition remains unknown and the observed decreases may result from nominal pre-ALD OM inputs. These results are the first to establish OM composition in ALD-impacted soil profiles, suggesting reallocation of permafrost-derived soil C to areas where degradation or erosion may contribute to increased C losses from disturbed Arctic soils.