Studies on the Permafrost Occurrence Related to the Past Climatic Changes in Antarctic Regions

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James Ross Island and Seymour Island locate in the middle of Weddel Sea near Larsen Ice Shelf. Due to the long periods of sea ice coverage, the mean annual temperature at both Islands is lower than western side of the Antarctic Peninsula and it stands -10^ﾟC.Ice free ground areas in both islands are exposed to the severe climatic conditions and permafrost develop in certain depths. To estimate the permafrost distribution, geo-eletric resistivity surveys were conducted at various locations.The vertical profiles of geo-electric resistivity of the ground indicate the existance of the discontinuity of resistivity. The depth of this discontinuity relates to the permafrost table. The horizontal profiles of geo-electric resistivity at the sorted circles show the internal structure of the frozen ground.At James Ross Island, marine terraces develop at three different altitudes ; upper terrace (+30-40 m a. s. l.), middle terrace (+15-20 m a. s. l.) and lower terrace (+5 m a. s. l.). The ages of middle and lower terraces were estimated by the results of ^<14>C dating measurements using shell samples as 25,000y. B. P. and 3,000y. B. P., respectively. The depth of the permafrost table at lower terrace is estimated as 6 m. It implies that the permafrost with 6 m depth formed for these 3000 years under the present climatic condition.Besides of permafrost occurrence at the surveyed areas, active periglacial phenomena were observed such as sorted stripes, sorted circles and stone pits. Transitional distributions of sorted circles and stone pits were mapped in detail on the slope. To monitor the active ice-wedge cracking under present climatic condition, the distance between the ice-wedge ice were measured with non-active cracking for two years periods.