Characteristics and Significance of the Transition Zone in Drained Thaw-Lake Basins of the Arctic Coastal Plain, Alaska

In the three-component conceptual model of arctic soils, the transition zone is recognized as a layer intermediate between the seasonally thawed active layer above and the stable permafrost below. Although typically frozen and therefore part of the near-surface permafrost, the transition zone episodically thaws over a time period ranging from sub-decadal to multicentennial. From an analysis of 138 pedons from the Arctic Coastal Plain near Barrow, Alaska, we were able to delineate the upper boundary of the transition zone in 78% and the lower boundary in 70% of the pedons. The transition zone exhibits the effects of cryoturbation, contains abundant redistributed organic carbon, is enriched by ice in the forms of lenses, veins, and nets (reticulate vein ice) and has abundant soil moisture. The surface (upper boundary) of the transition zone is found at an average depth of 34 ± 7 cm below the ground surface and has an average thickness of 23 ± 8 cm. We observed no significant differences in the thickness of the transition zone or the depth of its boundaries in drained thaw-lake basins ranging in age from 300 to 5500 years BP, suggesting that the processes leading to the development of this zone occur rapidly in Arctic Alaska. Recognition of the transition zone has implications for understanding pedogenic processes in permafrost-affected soils and for determining the response of near-surface permafrost to climate warming.Dans le modèle conceptuel à trois composantes des sols arctiques, la zone de transition est reconnue comme une couche intermédiaire entre la couche active supérieure qui dégèle selon les saisons et le permafrost stable au-dessous. Bien qu’elle soit généralement gelée et que par conséquent, elle fasse partie du permafrost près de la surface, la zone de transition dégèle de manière épisodique sur une période allant de moins d’une décennie à plusieurs centaines d’années. D’après l’analyse de 138 pédons provenant de la plaine côtière de l’Arctique près de Barrow, en Alaska, on a pu délimiter la borne supérieure de la zone de transition dans 78 % des pédons et la borne inférieure dans 70 % d’entre eux. La zone de transition affiche les effets de la cryoturbation, puis elle contient du carbone organique distribué en abondance, elle est enrichie par la glace sous la forme de lentilles, de veines et de réseaux (glace de veine réticulée) et son sol renferme une humidité abondante. La surface (borne supérieure) de la zone de transition se trouve à une profondeur moyenne de 34 ± 7 cm sous la surface du sol et son épaisseur moyenne est de 23 ± 8 cm. Aucune différence considérable n’a été observée quant à l’épaisseur de la zone de transition ou à la profondeur de ses bornes dans les bassins de lacs de dégel allant de 300 à 5 500 ans BP, ce qui laisse croire que les processus ayant mené au développement de cette zone se produisent rapidement dans l’Alaska arctique. La reconnaissance de la zone de transition a des incidences sur la compréhension des processus pédogénisés dans les sols affectés par le permafrost ainsi que sur la détermination de la réaction du permafrost situé près de la surface au réchauffement du climat

Diurnal Thermal Regime in a Peat-Covered Palsa, Toolik Lake, Alaska

Strong spatial and temporal variations in temperature and effective thermal diffusivity are apparent from short-term thermal records measured in the peat atop an ice-cored palsa in northern Alaska. Intersite differences in near-surface temperature regimes apparently result from topographic influences, vegetative cover, and site wetness. Values of effective thermal diffusivity indicate that ablation of the ice core is inhibited by advection of cold water near the ice-peat contact and by internal evaporation near the surface. These findings support the conclusions of earlier investigators, who emphasized the importance of peat for maintaining palsas near their equatorward limit.Key words: active layer, frost mound, palsa, peat, permafrost, soil temperature, thermal properties, AlaskaMots clés: couche active, tertre de gel, palsa, tourbe, pergélisol, température du sol, propriétés thermiques, Alask

Archaeal and bacterial communities across a chronosequence of drained lake basins in arctic Alaska

We examined patterns in soil microbial community composition across a successional gradient of drained lake basins in the Arctic Coastal Plain. Analysis of 16S rRNA gene sequences revealed that methanogens closely related to Candidatus ‘Methanoflorens stordalenmirensis’ were the dominant archaea, comprising >50% of the total archaea at most sites, with particularly high levels in the oldest basins and in the top 57 cm of soil (active and transition layers). Bacterial community composition was more diverse, with lineages from OP11, Actinobacteria, Bacteroidetes and Proteobacteria found in high relative abundance across all sites. Notably, microbial composition appeared to converge in the active layer, but transition and permafrost layer communities across the sites were significantly different to one another. Microbial biomass using fatty acid-based analysis indicated that the youngest basins had increased abundances of gram-positive bacteria and saprotrophic fungi at higher soil organic carbon levels, while the oldest basins displayed an increase in only the gram-positive bacteria. While this study showed differences in microbial populations across the sites relevant to basin age, the dominance of Candidatus ‘M. stordalenmirensis’ across the chronosequence indicates the potential for changes in local carbon cycling, depending on how these methanogens and associated microbial communities respond to warming temperatures

The role of low fat diets in the management of gall-bladder disease

Full text of this article is not available in the UHRAThis paper presents the results obtained from 87 questionnaires completed by dietitians about the dietary management of gall-biadder disease. Of the patients referred to the dietitians, 86% were referred by surgeons. Of the dietitians that responded 77% thought that there was a role for low fat diets in the management of these patients; 92% would advise a low fat diet to help avoid pain, and 11% would advise a low fat diet to patients with gall-bladder disease who did not have pain, steatorrhoea or obesity. The paper reviews the available evidence concerning the effect of dietary fat on the gall-bladder; it is concluded that, at present, there is little data to support the therapeutic use of a low fat diet for individuals with gall-stones.Peer reviewe