Abstract
The authors conducted a field survey related to the genesis and occurrence of permafrost in James Ross Island and Seymour Island, Antarctic Peninsula region, during the 1989-1990 Antarctic summer season. Mean annual air temperature in both islands is estimated at about-10°C.
Seymour Island is located in the Weddell Sea. There was no ice-sheet over the island during or since the last glaciation period. Marine terraces of three different levels are distributed in the is-land: an upper terrace at Meseta (about 200 m a. s. 1.), a middle terrace at Sub-Meseta (about 50 m a. s. 1.) and a lower terrace at Larsen (about 5 m a. s. 1.). In order to estimate the thickness of permafrost, geo-electric resistivities were surveyed on these terraces. In the lower terrace at Larsen, long-term monitoring of ground temperature profiles was carried out for two years. The annual mean ground temperature and the temperature gradient indicate that the permafrost base is 34 m deep. This coincides with the depth obtained by geo-electric resistivity measurements.
In James Ross Island, about 90% of the ground surface is covered with an ice sheet or glaciar. Ice-free ground spreads to the northwestern part of the island. Coastal terraces of three different levels develop around Santa Marta Point along Croft Bay: upper terrace(21-24 m, 32-35 m a. s. 1.), middle terrace (10-17 m a. s. 1.) and lower terrace (3-5 m a. s. 1.). The group of upper terraces is composed of glacial till or fluvio-glacial deposits. Shell samples were collected from the deltaic deposit which composes the middle terrace, and from marine sands and gravels which cover the surface of the lower terrace. Then 14C dating was done with the results of about 25, 000 y. B. P. and 3, 000 y. B. P. respectively. According to geo-electric resistivity measurements, the depths of permafrost bases on the upper and lower terraces are estimated at 40 m and 3-5 m, respectively. It is considered that permafrost on the upper terrace occurred prior to the last glacial maximum age. The comparison between Antarctic and Arctic permafrost suggests that the permafrost in Antarctic regions is shallower than that in Arctic regions under similar annual mean temperatures at the present time.
