Abstract
We describe the distribution and morphology of well-developed large-scale sorted circles and polygons from the northern Billefjorden, central Svalbard, and we analyze their relation to environmental conditions. The sorted circles and polygons are found mainly on raised marine and kame terraces at elevations up to 200-250 m asl and on adjacent flat-topped mountain ridges above elevations of around 600 m asl.
These two distinct regions are separated by steep, scree-covered slopes unfavourable for patterned-ground development. The diameters of the sorted circles and polygons range from several decimetres to up to 450 cm with an average of 198 cm and 154 cm for length and width, respectively.
The average height is 16 cm, but it reaches up to 50 cm depending on the pattern diameter. For feature widths of 146 to 164 cm, sorting depths range between 44 to 64 cm giving width-to-sorting depth ratios from 2.41 to 3.73, which is roughly consistent with models of patterned-ground formation involving circulation mechanisms.
Generally, higher elevations host significantly smaller and less up-domed patterns than lower elevations. Likewise, shallower sorting occurs at higher altitudes, though the sample is not representative.
We explain these altitudinal changes in patterned-ground morphology by decrease of active-layer thickness towards higher elevations. This suggests that large-scale sorted patterned ground can be an indicator of climate conditions.
On the other hand, permafrost table was achieved only at one excavation site located near sea level and reached 36 cm below the sorting depth. At other two excavation sites, permafrost table was not encountered up to 10 cm below the sorting depth.
Therefore, we believe that, at least in lower elevations, sorted circles and polygons are likely not in equilibrium with present-day climate conditions. We also infer that patterned-ground development in the high-Arctic environment can take place on timescales of hundreds of years.