Yedoma
- Contents
- Yedoma
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Yedoma (ice complex) is organic-rich Pleistocene loess permafrost, containing methane (one of the global warming gases). Therefore, global warming may promote a positive feedback, due to melting yedoma.
Yedoma is closely related to the development of ice wedge. - Yedoma in northeastern Siberia along the Arctic Sea
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[Left] Bob Sento collected ice samples for measure dating Yedoma. The survey was conducted along East Siberian Sea near Ambarchik on August 13 1996. [Right] We can see baidzharakhs in the backyard of yedoma. - Ice wedge
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Large masses of ice growing in thermal contraction cracks in permafrost zones
Gullies developed by ice wedges along Kolyma River, northern SiberiaVegetation structure was surveyed in gullies developed by the melting of ice wedges along the Kolyma River, northern Siberia, using 72 50 × 50 cm plots. The mean total plant cover was approximately 50% on gley soils, which were only distributed in the gullies. Based on twinspan cluster analysis, four vegetation types were recognized: (i) Agrostis purpurascens grassland with Ceratodon purpureus moss carpet; (ii) Matricaria matricarioides forbland; (iii) Chamaenerium angustifolium and M. matricarioides forbland; and (iv) Descurainia sophia grassland. Species that produce seeds capable of long-distance dispersal established well. Of the environmental factors surveyed, the gully scales (height and width) and elevational difference within a plot were primarily related to the vegetation development. The gully height was correlated with soil pH and compaction that might be related to intensities of ground surface disturbances. Agrostis purpurascens established in large gullies, while Equisetum arvense and Salix alaxensis established in small gullies. Soil compaction was also related to the vegetation establishment patterns (e.g. Rumex sibirica did not establish on hard soils). We concluded that the gully scales primarily determine soil conditions, including ground surface instability as a function of slope and soil compaction, and subsequent community structure.
- Baidzharakh
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Baidzharakhs or baidzherakhs (Sakha language) develop on coastal terraces in the northern Siberian arctic tundra facing the Arctic Ocean, and develop around ice wedges and edomas. A network of baidzharakhs is derived from frozen thermo-erosional mounds in the permafrost zone. A baidzharakh is a mound several meters high and 3-12 m wide. It is the residual shell formed by the melting of ice wedges in polygonal ground. However, the formation processes have various developmental pathways, including abundant ice pillars covered by a frozen earth layer occurring on glacial terraces, and washing out by flows of earthy veins.
To understand how baidzharakhs (relic mounds enclosing polygonal ice blocks in permafrost) aVect the zonal distribution of vegetation, vegetation was measured in 145 plots of area 50 cm × 50 cm on a coastal terrace facing the Arctic Ocean in northern Siberia. Cluster analysis classified five community types that were zonally distributed along the coastline. α-diversities (species richness and diversity) were not different among vegetation types except for vegetation close to the coastline. On and around baidzharakhs, burrows created by lemmings were frequently observed, and plant cover was low, suggesting that baidzharakhs support habitats for rodents. Disturbances by rodent habits caused plant cover to decline but did not change α-diversity. Two vegetation types that developed only on baidzharakhs were found at intermediate distances between the seacoast and inland areas. Because these two vegetation types are azonally distributed, β- and γ-diversities were increased by permafrost-derived topography, i.e., baidzharakh, and/or disturbance by rodents of which suitable nesting habitat is provided by baidzharakh.
- References
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- permafrost
- wetland (湿原)
- Sento B (仙頭ボブ). 1996. ちょっと、ほんまにそれやんの? 北海道大学大学院 地球環境研究科 地圏環境科学専攻 地球雪氷学講座 修士論文(裏版)