始新世-渐新世界线的全球气候事件：从“温室”到“冰室”

新生代以来,全球气候在持续不断的变冷,从两极无冰的"温室地球"变为现今两极终年有冰的"冰室地球",经历了多次冰盖扩张的变冷事件。始新世-渐新世界线（E/O）附近,δ¹⁸O值大幅度正偏,在短期内由 1．2‰迅速增加到 3．0‰,底层海水温度从12 ℃降低为 4．5 ℃。保存在大洋和大陆中的记录表明：E/O界线附近,全球气温大幅降低,海陆生物均有不同程度的灭绝,指示了气候变冷、变干的趋势。始新世-渐新世转换期间,南极洲与澳大利亚之间的塔斯曼尼亚海道和南极洲与南美洲之间的德雷克海峡（DrakeStrait）相继打开,形成环南极洋流,从而阻止赤道地区的热量向南极传送,导致南极大陆"热隔绝",使南极大陆东部为冰川所覆盖。最近的研究显示,E/O事件是与大气CO₂含量快速变化密切相关的瞬时气候变化,其变化速率类似于现今地球由于人类活动引起大气CO₂的变化,表明大气CO₂浓度的变化在这一事件中起了极为重要的作用。

GLOBAL CLIMATE EVENT AT THE EOCENE-OLIGOCENE TRANSITION: FROM GREENHOUSE TO ICEHOUSE

During Cenozoic, Earth's climate has undergone a progressive cooling, from bipolar ice-free ( greenhouse) to bipolar icesheets (icehouse), experienced several icesheet growth and decay events. At the Eocene-Oligocene boundary (E/O), δ¹⁸O increased rapidly from 1.2‰ to 3.0‰ in a short time, deep-sea temperature decreased from 12℃ to 4.5℃. The marine and terrestrial records show that near the E/O, global temperature has a significant decreasing, the biotic extinctions happened both in ocean and land, indicating the cooling and drying trend on global climate. During the Eocene-Oligocene transition, the Tasmania Seaway (between the Antarctic and the Australia) and the Drake Passage (between the Antarctic and South America) opening and widening, it may caused the formation of the Antarctic Circumpolar Current and the subsequent thermal isolation of the Antarctic continent, which formed the East Antarctic Ice Sheet. The last research finds that the E/O event is an instantaneous climate change, which has a close relationship with the atmospheric CO₂ concentration viriation. Its change rate similar with the atmospheric CO₂ concentration diversification reduced by humankinds activity at present, implying that the atmospheric CO₂ concentration viriation play a more important role than the opening of the passages in the E/O event.