ALBERT

Description: Measured methane concentrations in the ice cover of ponds and lakes on Samoylov Island (Lena-River-Delta in northern Siberia). Methane concentration were extracted from ice core samples. The location of each sample relative to the lake surface is indicated by a minimum and maximum depth. The ice cores were extracted by cutting ice columns to a depth of about 70 cm from the ice cover. The ice samples were melted in 1 L plastic containers. Methan concentration were obtained by head-space analysis. For a detailed description of the methods see Langer et al. (2015).

Description: This dataset is a compilation of 1,207 lake basal ages used to identify spatial and temporal patterns of lake formation across the high northern latitudes. Data was gathered from scientific literature descriptions of lake cores, peat cores underlain by lake sediments, and exposures within the domain of glaciation and permafrost extent during the Last Glacial Maximum. We distinguished eight classes of lake origin. Where not indicated by the author, we sought to determine lake origin from lithology, geological history and site descriptions within the text. Though most records (95%) were radiocarbon dated, we included robust dates obtained by a variety of methods including varve counting, photoluminescence, Pb/Cs, Th/U, wiggle matching and tephrochronology. We reported oldest sample ages in the majority of cases, electing not to utilize basal ages derived from age-depth models extrapolated beyond dated levels due to both their high level of uncertainty and differences between methodologies used to construct each model. We excluded dates from shallow lake cores that clearly did not reach basal lake sediments, or that were collected for the sole purpose of methods development or recent human impact studies. Records that did not include dates from lower-most cored sediments, that suffered from uncorrected reservoir effects (noted by original author) or that contained copious age reversals were also excluded. Some records provided distinct stratigraphic evidence of lake formation that allowed for exact determination of lake basal age, while other lithologies were more ambiguous. To address this uncertainty, we categorized each lake age as "minimum" or "basal" based on interpretation of contextual, geographical and lithological information.

Description: Permafrost-related processes drive regional landscape dynamics in the Arctic terrestrial system. A better understanding of past periods indicative of permafrost degradation and aggradation is important for predicting the future response of Arctic landscapes to climate change. Here, we used a multi-proxy approach to analyze a ~4 m long sediment core from a drained thermokarst lake basin on the northern Seward Peninsula in western Arctic Alaska (USA). Sedimentological, biogeochemistical, geochronological, micropaleontological (ostracoda, testate amoeba) and tephra analyses were used to determine the long-term environmental Early-Wisconsin to Holocene history preserved in our core for Central Beringia. Yedoma accumulation dominated throughout the Early to Late-Wisconsin but was interrupted by wetland formation from 44.5 to 41.5 ka BP. The latter was terminated by deposition of 1 m of volcanic tephra, most likely originating from the South Killeak Maar eruption at about 42 ka BP. Yedoma deposition continued until 22.5 ka BP and was followed by a depositional hiatus in the sediment core between 22.5 and 0.23 ka BP. We interpret this hiatus as due to intense thermokarst activity in the areas surrounding the site, which served as a sediment source during the Late-Wisconsin to Holocene climate transition. The lake forming the modern basin on the upland initiated around 0.23 ka BP, which drained catastrophically in spring 2005. The present study emphasizes that Arctic lake systems and periglacial landscapes are highly dynamic and permafrost formation as well as degradation in Central Beringia was controlled by regional to global climate patterns and as well as by local disturbances.