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.

Description: The millions of ponds and small lakes in Arctic lowlands have been identified as biogeochemical hotspots with high process rates regarding the turnover of energy and carbon. The rapidly warming Arctic climate does affect the surface inundation due to changes in the water balance and/or permafrost degradation which directly alters the exchange of energy and carbon between the surface and the atmosphere. However, these water bodies with surface areas smaller than 1 km² are not captured on a global scale due to the low resolution of global maps. High-resolution imagery allows to map ponds and small lakes but provides only limited coverage. This study aims to identify landscape-specific parameters which allow to upscale high-resolution but local water body size distributions to the pan-arctic scale. Water bodies are mapped from aerial, TerraSAR-X and Kompsat-2 imagery with resolutions of 4 m and better in 9 major Arctic landscapes in Russia (Lena River Delta, Yamal Peninsula, Indigirka Lowlands), Canada (Canadian High Arctic, Mackenzie River Delta, Yellowknife) and Alaska (Barrow Peninsula, Yukon Delta, Seward Peninsula). Water body size distributions are parameterized via their mean, standard deviation and skewness. We assess (i) similarities between the high-resolution distributions and existing regional and global water body databases, as well as (ii) the variability of water body size distributions within and between regions, and (iii) relate regional differences to hydrological, geomorphological and permafrost processes. Ponds make more than 95% of the total number of water bodies in all landscapes except the Mackenzie Delta, where they contribute only about 75%. Within-landscape variability is low in all study areas which allows the estimation of regional distributions. The statistical properties of these regional distributions can be used to incorporate ponds and small lakes into larger-scale climate and ecosystem models. This study provides a pan-arctic estimate of small ponds and lakes which represents a baseline against which to evaluate climate-induced changes in the distributions of Arctic water bodies.

Description: Author(s): Devang A. Joshi, P. Burger, P. Adelmann, D. Ernst, T. Wolf, K. Sparta, G. Roth, K. Grube, C. Meingast, and H. v. Löhneysen The magnetic behavior of single-crystalline CeCuGa 3 has been investigated. The compound forms in a tetragonal BaAl 4 -type structure consisting of rare-earth planes separated by site-disordered Cu-Ga layers. If the Cu-Ga site disorder is reduced, CeCuGa 3 adopts the related, likewise tetragonal, BaNiSn ... [Phys. Rev. B 86, 035144] Published Wed Jul 25, 2012