全新世晚期南极乔治王岛菲尔德斯半岛的海平面变化

在考察南极菲尔德斯半岛自然地理特征的基础上 ,分析了半岛东侧阿德雷岛西部海拔18 0 0m的海岸阶地上苔藓泥炭层 (0～ 44cm)之沉积特征 ,分别测量了 5 5～ 8cm ,18～ 2 0cm ,36～38cm三个层段泥炭样品的14 C年龄为 :现代、(6 71± 2 0 )aBP、(32 6 5± 12 0 )aBP ,据此推算该苔藓泥炭底层形成的时间大约在 430 0aBP。分析了半岛西北部地质湾海滩沉积层中同种浅海底栖褐藻 (Ha lymeniasp )的14 C年龄 ,即 15～ 17cm和 92～ 95cm层中褐藻的14 C年龄分别为 (885± 70 )aBP、(144 0±75 )aBP ,现代褐藻14 C年龄为 (6 95± 70 )aBP。用不同时段褐藻14 C年龄内差法消除南极海源有机碳的14 C年龄老化问题 ;还分析了地质湾海拔 6 84m海岸阶地古湖相硅藻沉积层的14 C年龄为 (2 430±75 )aBP。从而建立了全新世晚期南极菲尔德斯半岛的海平面变化序列 :在 430 0～ 2 430aBP期间 ,区域海平面快速下降 ,其平均下降速率为 - 0 6 0cm·a-1;在 2 430～ 80 0aBP期间 ,区域海平面继续下降 ,其平均下降速率为 - 0 31cm·a-1;在 80 0～ 2 30aBP期间区域海平面开始缓慢上升 ,其平均上升速率为 0 14cm·a-1;近 2 30a来海平面上升进一步趋缓 ,其平均上升速率为 0 0 7cm·a-1。

LATE HOLOCENE SEA-LEVEL CHANGES IN FILDES PENINSULA,ANTARCTICA

Sea level change in Antarctica is of current interest because of its possible sensitivity to global climate change. A detailed record of sea level changes during the Late Holocene is preserved in the coastal environment of Fildes Peninsula, where 6 coral reef terraces were found. The radiocarbon ages of the moss peat banks on the terrace (altitude 18.00m), the diatom layer deposited in the ancient lake on the terrace (altitude 5.28m), and the marine alga layers deposited in the beach were analyzed. The results show: (1) The radiocarbon ages of the upper (5.5～8.0cm), the middle (18.0～20.0cm) , and the lower (36.0～38.0cm) moss peat layer are the present, (671±20)aBP and (3265±120)aBP respectively. It is shown by calculation that the mean accumulation rates of the subsurface layer (6.7～17.0cm) of the peat core and the lower layer (19.0～37.0cm) of the peat core are 0.195mm·a -1 and 0.069mm·a -1 respectively. Based on the mean accumulation rate and the radiocarbon age of the lower peat layer, it is shown by calculation that the forming age of the bottom peat is about 4300aBP. (2) The radiocarbon age of the marine alga in the layer of 15～17cm is (885±70)aBP, that in the layer of 92～95cm is (1 440±75)aBP, and the radiocarbon age of the modern marine alga is (695±70)aBP. And the ages were used to correct for the carbon reservoir effect of the marine alga. In the ancient lake bottom on the terrace, another 100cm×60cm profile was drilled, in which a layer of diatom deposited between 35 and 38cm with radiocarbon age of (2430±75)aBP exists. (3) During the period of 4300～2430aBP, the sea level of Fildes Peninsula fell 11.16 meters at an average of 0.60cm·a -1 ; during the period of 2430～800aBP, the sea level fell 4.98 meters at an average of 0.31cm·a -1 ; during the period of 800～230aBP, the sea level of Fildes Peninsula rose 78cm, the average rate of sea level rise was 0.14cm·a -1 ; during the last 230 years, the sea level rose 16cm, the average rate of sea level rise was 0.07cm·a -1 . Thus the average rate of sea level rise in Fildes Peninsula has gone up at a slower rate.