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Arctic Hydrology
Published in Yeqiao Wang, Coastal and Marine Environments, 2020
Bretton Somers, H. Jesse Walker
Permafrost is defined as earth material in which the temperature has been below 0°C for two or more years. Because it is defined only by its temperature, water is not necessary for its existence. However, most permafrost, which underlies more than 20% of the Earth’s land area, does contain ice in various amounts and forms. Ground ice occurs in the pores of the soil as lenses or veins and in large forms such as ice wedges.[6] By volume, pore ice is the largest, although ice wedges are more conspicuous. Where ice wedges are well developed, they may occupy as much as 30% of the upper 2 or 3 meters of the land surface. Their surface expression is distinctive and takes the form of ice-wedge polygons. In the Arctic, permafrost is continuous (Figure 16.1) except beneath those water bodies that are more than 2 meters deep and do not freeze to the bottom during winter. Permafrost is also present beneath near-shore waters off Siberia and North America.
Morphogenetic landforms
Published in Richard J. Chorley, Stanley A. Schumm, David E. Sugden, Geomorphology, 2019
Richard J. Chorley, Stanley A. Schumm, David E. Sugden
Much more common in terms of areal coverage are ice-wedge polygons, which bequeath a mosaic surface pattern to extensive low-lying areas of the Arctic. The polygons are commonly 15–40 m across and have three to seven sides, as befits a random pattern. Their sides are uplifted and separated by a narrow ditch. In summer their centres are marshy or even covered by water. The rims are underlain by ice wedges and the mode of formation is shown in Figure 18.29. In winter low temperatures below approximately – 19°C cause the ground to contract. As a result it cracks in a more or less random fashion (assuming uniform sediments and horizontal temperature gradients). In the next melt season the crack fills with water and a vein of ice forms in the permafrost below the active layer. In future years the ground cracks along the same line of weakness and allows the vein to widen into a wedge, eventually forcing sediment upwards to form ice-wedge rims. Ice-wedge polygons are part of a family of contraction-crack polygons. In arid areas the cracks may not fill with water and ice, but sand or other debris.
Dinosaur and tree-line invasion of southeastern Australia during Cretaceous greenhouse spikes
Published in Australian Journal of Earth Sciences, 2023
Paleosols give an additional paleoclimatic perspective because they can be arranged into categories typical of climate zones (Figure 9g). Frigid temperatures are indicated by a variety of periglacial features: clastic dykes (ice wedges), mud-load casts (periglacial convolution) and coal-mantled mudstone-rolls (string bogs or aapamires) in paleosols at Flat Rocks (Constantine et al., 1998), near Kilcunda, and in Wonthaggi coal mines (Edwards et al., 1944). MATs for ice wedge polygons are −8 to −4 °C, for microhummocks <1 °C, and for string bogs <0 to −1 °C (Williams, 1986). Ice-wedge polygons are characteristic of the tundra biome, but string bogs and periglacial involutions are found in taiga forest and subarctic tuckamores (Conaghan, 1984; Meades, 1990). Periglacial convolutions extend today into the cold temperate biome of discontinuous permafrost (Constantine et al., 1998). A rise from 4.3 ± 1.1‰ to 8.8 ± 0.9‰ in δ18OSMOW of early diagenetic carbonate nodules in the Otway and Strzelecki groups (Figure 9c) may correspond to a mean annual temperature rise from −4 ± 1.3 °C to +1 ± 1.0 °C (Figure 9b; Ferguson et al., 1999). Many paleosols from Flat Rocks west to Eagles Nest and from Cape Paton to Lavers Hill lack periglacial features but are thin, gleyed Inceptisols and Entisols characteristic of boreal forests (Retallack, 1997). Greenhouse CO2 spikes may have driven tree lines and their biomes southward in a manner comparable with modern global warming driving tree lines northward in the northern hemisphere (Harsch et al., 2009).
Early Cretaceous glacial environment and paleosurface evolution within the Mount Painter Inlier, northern Flinders Ranges, South Australia
Published in Australian Journal of Earth Sciences, 2020
S. B. Hore, S. M. Hill, N. F. Alley
Alley and Frakes (2003) defined the Livingston Tillite Member, flanking the northern Flinders Ranges in the lower MacDonnell Creek catchment, such as at ‘Recorder Hill’. In this area, periglacial facies such as solifluction and ice wedge casts are included within the ∼2 m-thick Bopeechee Regolith horizon that underlies the Cadna-owie Formation. Lower Cretaceous glacial sediments were later identified and recognised by Hore and Hill (2009a, 2009b) and Hill and Hore (2011), and are associated with hosting the Four Mile uranium mineralisation. These exposures were later referenced by Cross, Jaireth, Hore, Michaelsen and Schofield (2010), Roach, Jaireth and Costelloe (2014), Stoian (2010) and Woods and Jeuken (2010). Some glacial sediments located near Paralana Creek are further described and discussed by Alley et al. (2020) and this study. The Early Cretaceous glaciations recognised by Alley, Frakes, Sheard and Gray (2011) and Alley et al. (2020) identified three cold events that produced glacial ice at high latitudes.
Estimating methane emissions using vegetation mapping in the taiga–tundra boundary of a north-eastern Siberian lowland
Published in Tellus B: Chemical and Physical Meteorology, 2019
T. Morozumi, R. Shingubara, R. Suzuki, H. Kobayashi, S. Tei, S. Takano, R. Fan, M. Liang, T. C. Maximov, A. Sugimoto
Our investigation focussed on the taiga–tundra boundary ecosystem – Kodac site (K) (70.56° N, 148.26° E) – over the Indigirka lowland (Fig. 1). In this ecosystem, vegetation consists of mosaic patterns of sparse larch (Larix cajanderi, syn. L. gmelinii) stands, with a maximum height of 10 m (the density of the trees above 2 m in height is 341 trees ha−1 at site K [Liang et al., 2014]), shrubs (Betula nana) and wetlands. The soil is characterised by high organic content in the surface layer and abundant ice lenses (Iwahana et al., 2014). Regularly structured ice-wedge polygons and lakes are often observed in this ecosystem.