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

詹姆斯罗斯岛和西摩岛位于拉森冰架附近的韦德尔海中部。由于海冰覆盖的周期较长，两个岛屿的年平均气温都低于南极半岛西侧，为-10ﾟC。两岛的无冰地面地区都暴露在恶劣的气候条件下，并在一定深度发育永久冻土。为了估算多年冻土的分布，在不同的位置进行了地电阻率测量，地面的地电阻率垂直剖面显示了地电阻率不连续的存在。这种不连续的深度与永久冻土表有关。在詹姆斯罗斯岛，海相阶地发育在三个不同的高度：上阶地(+30-40米S，L)，中阶地(+15-20米，S，L)。和低阶地(+5米。S。L)。根据壳体样品25000年的测年结果，估算了中、下阶地的年龄。B.P.和3000年。分别为BP。估计下阶地的多年冻土台深度为6m，表明6m深的多年冻土是在目前的气候条件下形成的，除了调查地区存在多年冻土外，还观察到了冰缘活动现象，如分类条纹、分类圆圈和石坑。在坡面上详细绘制了分类圆圈和石坑的过渡分布图。为了监测当前气候条件下的活跃冰楔破裂，用两年的非活跃破裂测量了冰楔冰之间的距离。

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.