关键词: 乔治王岛;早第三纪;古气候;植物化石;大洋环流

Abstract:

The Fossil Hill flora from the Fildes Peninsula of the King George Island, Antarctica has been studied, which consists of more than. 40 forms of ferns, gymnosperms and angiosperms, being a mixture of subantarctic and neotropical elements, mostly resembling the Early Tertiary South American palaeoflora. According to "the nearest living relative method" and "leaf physiognomical analysis", the plants of the Fossil Hill flora probably grew under the following environmental conditions: 1. The mean annual temperature was approximately 14-16℃. 2. The mean temperature of the coldest month was about 10℃. 3. The mean temperature of the warmest month was about 20℃. 4. The mean annual range of temperature was probably 7-10℃. 5. There was a lack of solar radiation during winter as a result of being the high latitude. 6. There was high precipitation (more than 1000 mm per year). 7. The area where the plants of the Fossil Hill flora were growing was at rather low altitude. The author tried to determine what caused the warm and humid climate during the time when the plants were growing, and proposes the following hypothesis. During Cretaceous and Early-Middle Palaeogene, Antarctica, Australia and South America as parts of the Gondwana formed a nearly continuous landmass along the southern margin of the Pacific Ocean. The Southern Pacific was effectively separated from other oceans and continents at that time and it is reasonable to assume that in the Southern Pacific the oceanic circulation of a warm current southward from the equator transported huge quantity of heat to Gondwana. The Circum- Polar Current developed about 38 Ma ago; since then the antarctic climate began deteriorating. The development of a Circum-Polar Current as it exists today requires deep sea conditions around the whole of Antarctica; this did not appear until the end of the Oligocene.