Abstrakt
We describe the distribution and morphology of 290 sorted circles and polygons located at 16 study sites in the northern Billefjorden area, central Svalbard, and we investigate their relation to altitude. We further hypothesize about their developmental rates, chronology and relation to active-layer thickness (ALT) and present-day climate conditions.
One group of sorted circles and polygons (69 % of the investigated patterns) is located mainly on raised marine and kame terraces at elevations up to 200-250 m asl. A second group (31 %) occurs on adjacent flat mountain tops and ridges above elevations of around 600 m asl.
These two distinct elevation zones significantly differ in pattern morphology. The higher-elevated patterns have smaller diameters and shallower sorting depths due to a thinner active layer at higher elevations, suggesting that sorted patterned ground can be indicative of climate conditions and ground thermal state (i.e. permafrost or seasonally frozen ground) when the patterns initiated.
In contrast, the heights and height-to-width ratios of higher-lying sorted circles and polygons are larger. Bedrock lithology is believed to be of less importance for pattern morphology in the study area, causing only its fine-scale variations.
The ratios of pattern diameter-to-sorting depth in sorted circles and polygons have a median of 3.57, consistent with previous studies (median of 3.54) and theoretical models of patterned-ground formation involving circulation mechanisms. This allows estimation of the sorting depth based on patterned-ground surficial morphology, which can be used to reconstruct former active layers and associated temperature conditions.
Our findings suggest that large-scale sorted circles and polygons may develop over centennial timescales in this high-Arctic environment, unlike those in lower latitudes. Further, they are likely not in equilibrium with present-day climate conditions and have probably been forming throughout the Holocene.