永久凍土調査

Scientific expeditions in permafrost regions were carried out (1) Yakutsk, Siberia in the middle of August, 1972 and (2) Alaska and North Canada from the middle of June to the end of July, 1974.<BR>(1) Yakutsk, Siberia<BR>Field observations were carried out on permafrost around Lake Surdakh, which is located 250 km northeast from Yakutsk, Siberia. Lake Surdakh is an alas, which is a depression formed by a thermokarst development in which local deep thawing has taken place in permafrost masses accompanied by the melting of ground ice. The shape of the alas is nearly round and the diameter of Lake Surdakh is about 4 km. The lake is surrounded from all sides by a larch forest. The height of the basin cliffs is about 20 m. At some places along the cliffs underground ices are exposed. The top of the ices is 1.5 m below the top of the cliffs and the ices sink into the ground in a wedge-like shape. Field observations were made as to the exposed ice, the soil around the exposed ice and the forest above the ground.<BR>(2) Alaska and North Canada<BR>The group was divided into three sub-groups according to their research subjects : <BR>(i) frozen ground (ii) vegetation and (iii) soil invertebrates.<BR>(i) Frozen ground Drilling programmes were carried out at the following locations by using a portable boring machine : three spots on polygons at Barrow ; one in a Polygon and four at Ibyuk Pingo in Tuktoyaktuk ; two at Caribou Hill near Reindeer Depot. Core samples of 4.5 cm in diameter were taken from the surface to a depth of 140 cm for analysis of their layer structures, soil colors, densities and pH's. These samples were dried in an oven, and measurements were made as to the water contents, densities and size distributions of the soil particles contained.<BR>Ice lumps were picked up from ice layers in an ice tunnel (Fox, Fairbanks), an ice cellar (Tuktoyaktuk village), one of the ice wedges and one of the buried ice masses which were exposed along the seacoast of Kugmallit Bay 6 km from Tuktoyaktuk village to the southwest. These ice lumps and the ice cores which were taken during the drilling were sliced and observed under the polarized light for analysis of their crystal structures. It was found that the samples of ice from the above contained air bubbles and dirts, both of which were aligned in stripes, and the texture was poly-crystalline ; the crystal sizes were several millimeters.<BR>These ice samples which were melted there were brought back to Japan for measurement of the ratio of ¹⁸O/¹⁶O. Also a ¹⁴C analysis was done on the organic materials which were included within the core samples.<BR>(ii) Vegetation Permafrost is an important ecological factor in the subarctic forests, and the knowledge of its relationship to a vegetation process is important for an understanding of forest ecology of northern regions. On the warm, well drained sites such as southern slopes and sides of rivers, white spruce trees or white spruce-paper birches grow, while on poorly drained sites including plateaus, flats and north-facing sites, stunted black spruce trees with moss layers of Sphagnum spp. are predominant. We observed that the depths of the active layer and drainage are of special importance in the vegetation and succession of trees on permafrost near Inuvik.<BR>(iii) Soil invertebrates Sod samples (each 19.6 cm²× 8 cm) were taken from various habitats. Soil invertebrates were picked up from the samples. The total number of soil invertebrates which were picked up at Ibyuk Pingo was 1974, of which 81.6% was found in the layer of 0-2 cm in depth, 15.1% 2-5 cm and 3.3% 5-8 cm. The composition of soil fauna and their individual numbers were as follows : Collembola : 743, Nematoda : 548 ; Acarina : 469 ; Chironomidae : 22 ; Enchytraeidae : 11 ; Tardigrada : 1 ; Trichoptera 1.