Description: Permafrost degradation influences the morphology, biogeochemical cycling and hydrology of Arctic landscapes over a range of time scales. To reconstruct temporal patterns of early to late Holocene permafrost and thermokarst dynamics, site-specific palaeo-records are needed. Here we present a multi-proxy study of a 350-cm-long permafrost core from a drained lake basin on the northern Seward Peninsula, Alaska, revealing Lateglacial to Holocene thermokarst lake dynamics in a central location of Beringia. Use of radiocarbon dating, micropalaeontology (ostracods and testaceans), sedimentology (grain-size analyses, magnetic susceptibility, tephra analyses), geochemistry (total nitrogen and carbon, total organic carbon, d13Corg) and stable water isotopes (d18O, dD, d excess) of ground ice allowed the reconstruction of several distinct thermokarst lake phases. These include a pre-lacustrine environment at the base of the core characterized by the Devil Mountain Maar tephra (22,800 +/- 280 cal. a BP, Unit A), which has vertically subsided in places due to subsequent development of a deep thermokarst lake that initiated around 11,800 cal. a BP (Unit B). At about 9,000 cal. a BP this lake transitioned from a stable depositional environment to a very dynamic lake system (Unit C) characterized by fluctuating lake levels, potentially intermediate wetland development, and expansion and erosion of shore deposits. Complete drainage of this lake occurred at 1,060 cal. a BP, including post-drainage sediment freezing from the top down to 154 cm and gradual accumulation of terrestrial peat (Unit D), as well as uniform upward talik refreezing. This core-based reconstruction of multiple thermokarst lake generations since 11 800 cal. a BP improves our understanding of the temporal scales of thermokarst lake development from initiation to drainage, demonstrates complex landscape evolution in the ice-rich permafrost regions of Central Beringia during the Lateglacial and Holocene, and enhances our understanding of biogeochemical cycles in thermokarst-affected regions of the Arctic.

Description: Increasing air temperatures are changing the arctic tundra biome. Permafrost is thawing, snow duration is decreasing, shrub vegetation is proliferating, and boreal wildlife is encroaching. Here we present evidence of the recent range expansion of North American beaver (Castor canadensis) into the Arctic, and consider how this ecosystem engineer might reshape the landscape, biodiversity, and ecosystem processes. We developed a remote sensing approach that maps formation and disappearance of ponds associated with beaver activity. Since 1999, 56 new beaver pond complexes were identified, indicating that beavers are colonizing a predominantly tundra region (18,293 km2) of northwest Alaska. It is unclear how improved tundra stream habitat, population rebound following overtrapping for furs, or other factors are contributing to beaver range expansion. We discuss rates and likely routes of tundra beaver colonization, as well as effects on permafrost, stream ice regimes, and freshwater and riparian habitat. Beaver ponds and associated hydrologic changes are thawing permafrost. Pond formation increases winter water temperatures in the pond and downstream, likely creating new and more varied aquatic habitat, but specific biological implications are unknown. Beavers create dynamic wetlands and are agents of disturbance that may enhance ecosystem responses to warming in the Arctic.

Description: Permafrost acts as an impermeable subsurface in Arctic lowland landscapes. This hydrological barrier results in carbon-rich, water-saturated soils as well as many ponds and lakes. The rapidly warming Arctic climate very likely will affect the surface inundation in Arctic lowlands due to changes in precipitation, evapotranspiration, and permafrost degradation. Drying and wetting of the surface may occur in different regions and potentially alter the exchange of energy and carbon between the surface and the atmosphere. With increased permafrost thaw, for example, water may drain to deeper soil layers or drainage maybe enhanced due to newly forming drainage networks. Melting ground ice and subsequent inundation, on the other hand, may enhance formation of new ponds and wet areas. The current distribution of ponds and lakes in the Arctic is the result of complex interactions between climate, ground ice volume, topography, age and sediment characteristics. Because lake formation and growth processes occur at spatial scales orders of magnitude below those of the resolution for global or pan-arctic models land surface models, statistical representations of lake size distributions and other properties to inform such processes in future models are needed that can be related to macroscopic landcape properties. This study proposes basic observationally-constrained relationships to enhance the modeling of future Arctic surface inundation. We mapped ponds and lakes in 21 circum-arctic sites representing different permafrost-soil landscapes, i.e., physiographic regions with similar surface geology, regional climate, and biomes. We used high-resolution optical and radar satellite imagery with spatial resolutions of 4 m or better to create detailed water body maps and derive representative probability density functions (PDF). PDFs of ponds and lakes vary little within the same ecoregion. Significant differences, however, do occur between landscapes. We used regional permafrost-soil landscape maps of Alaska, Canada, and Siberia to upscale the water body distributions to the circum-arctic. We here present regional distribution parameters, i.e. pond and lake fractions as well as PDF moments (mean surface area, standard deviation, and skewness) and their uncertainties. Younger landscapes, that developed in the early Holocene exhibit very skewed water body distributions. These landscapes are dominated by many ponds and feature only very few large lakes. Older landscapes, on the other hand, show more larger lakes but also a higher variability in pond and lake size. For lakes smaller than 5*10⁵ m², PDFs change in a regular fashion across all sites: Relationships between mean surface area and standard deviation show a linear behaviour whereas the correlation between mean and skewness log-normal. We hypothesize that these relationships are an expression of pond and lake growth and/or lake formation in the landscapes and discuss the potential of the observed patterns to improve predictions of future distributions of Arctic ponds and lakes.