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

Abstract

ABSTRACT. 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.Key words: active layer, Alaska, arctic soils, frozen ground, permafrost, transition layer RÉSUMÉ. 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 transitio...

Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

“…Active layers, the uppermost layers of the ground that freeze and thaw annually, are typically 15e 40 cm thick (Bockheim and Hinkel, 2005). July is the warmest month, and July mean air temperature increases from 4 C at Point Barrow on the coast to 12 C at near the Brooks Range (Zhang et al, 1996).…”

Cryopedology

“…At the surface is the "active layer" which thaws in summer and refreezes in winter. However, recent research in North America supports an earlier Russian proposal for the existence of a "transition" or "transient" layer in arctic soils (Shur et al 2005;Bockheim and Hinkel 2005). This layer is the uppermost, or near-surface, portion of the permafrost and meets the thermal criteria defined above.…”

“…The transition zone exhibits the effects of cryoturbation, contains abundant redistributed organic carbon, is enriched in ice in the forms of lenses, veins and reticulate vein ice (nets), and has abundant soil moisture. In Arctic Alaska, the surface of the transition zone was found at an average depth of 34 ± 7 cm below the ground surface and had an average thickness of 23 ± 8 cm (Bockheim and Hinkel 2005). They observed no significant differences in the depth of the boundaries and thickness of the transition zone in drained thaw-lake basins ranging in age between 300 and 5,500 year BP, suggesting that the processes leading to its development occur rapidly in arctic Alaska.…”

Thermal characterization of the active layer at the Limnopolar Lake CALM-S site on Byers Peninsula (Livingston Island), Antarctica

“…3) could point towards the presence of a former transition layer or a zone-like relict transition in the ground (e.g., Bockheim and Hinkel, 2005). Many other observations and calculations point in that direction.…”

“…In early February 2009, a new monitoring site following the protocols of the Circumpolar Active Layer Monitoring South (CALM-S) program (e.g., Brown et al, 2000;Matsuoka and Humlum, 2003;Nelson et al, 2004;Matsuoka, 2006) was established in the Limnopolar basin (62 • 34 35 S, 61 • 13 07 W) ( Fig. 1), on Byers Peninsula, Livingston Island (South Shetland archipelago), Antarctica .…”