Abstract
ABSTRACT Ice-wedge polygons are common features of northeastern Siberian lowland periglacial tundra landscapes. To deduce the formation and alternation of ice-wedge polygons in the Kolyma Delta and in the Indigirka Lowland, we studied shallow cores, up to 1.3 m deep, from polygon center and rim locations. The formation of well-developed low-center polygons with elevated rims and wet centers is shown by the beginning of peat accumulation, increased organic matter contents, and changes in vegetation cover from Poaceae-, Alnus-, and Betula-dominated pollen spectra to dominating Cyperaceae and Botryoccocus presence, and Carex and Drepanocladus revolvens macro-fossils. Tecamoebae data support such a change from wetland to open-water conditions in polygon centers by changes from dominating eurybiontic and sphagnobiontic to hydrobiontic species assemblages. The peat accumulation indicates low-center polygon formation and started between 2380 ± 30 and 1676 ± 32 years before present (BP) in the Kolyma Delta. We recorded an opposite change from open-water to wetland conditions because of rim degradation and consecutive high-center polygon formation in the Indigirka Lowland between 2144 ± 33 and 1632 ± 32 years BP. The late Holocene records of polygon landscape development reveal changes in local hydrology and soil moisture.
Highlights
Permafrost regions are strongly affected by ongoing global warming (ACIA 2004)
We studied the cryolithology and micropalaeontological inventory of ice-wedge polygons in the Kolyma Delta near Pokhodsk (N 69.079184°, E 160.963365°), while we obtained one additional data set from a polygon center in the Indigirka Lowland approximately 550 km to the west near the World Wildlife Foundation (WWF) Kytalyk research station (N 70.827232°, E 147.490542°) for comparison (Figure 1; Schirrmeister et al 2016)
The peat of polygon centers differs from the underlying minerogenic deposits by slightly decreasing δ18O and δD and increasing d excess as seen in core 12P-1907-2 (Figure 2) of intrasedimentary ice, which is present in the peat as pseudoataxitic, structureless, or porphyric cryostructures
Summary
Permafrost regions are strongly affected by ongoing global warming (ACIA 2004). The widely distributed patterned ground of Arctic polygonal wetlands is considered to be sensitive to environmental and climate changes (Liljedahl et al 2016). Ice-wedge polygons occur abundantly in the Canadian Arctic, in the Alaskan Arctic coastal plains, and in northern Siberian lowlands. Circumarctic polygonal wetlands cover about 250,000 km (Minke et al 2007). Ice-wedge polygons form either low (often pond filled) polygon centers, which are surrounded by elevated peaty polygon rims underlain by ice wedges or high-center polygons in which the center is elevated and surrounded by polygon trenches underlain by melting ice wedges (MacKay 2000). Soils in permafrost regions consist of the seasonally unfrozen active layer and the underlying, perennially frozen ground (Ellis et al 2008)
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