Late Oligocene initiation of the Antarctic Circumpolar Current: evidence from the South Pacific
Late Oligocene initiation of the Antarctic Circumpolar Current: evidence from the South Pacific
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渐新世晚期南极绕极流的起始：来自南太平洋的证据
作者：
M. Lyle;S. Gibbs;T. C. Moore;D. Rea
南极绕极流（ACC）是南大洋的一个重要特征。它的发展可能帮助南极洲降温，并开始了南半球的冰川作用。在塔斯曼通道（位于南极洲和澳大利亚之间）和德雷克通道（位于南美洲和南极洲之间）打开之后，太平洋环流的深层环流就建立起来了。然而，从始新世中期到中新世早期，估计ACC的起始时间超过20m。来自南太平洋的上渐新世至全新世沉积物的新活塞岩心使我们能够将ACC的形成划为晚渐新世（约25-23 Ma）。上渐新世、水流作用沉积和上中新世的断陷是现代ACC流开始的结果；例如，在整个水柱中建立了强流和混合。以前发表的Nd同位素数据确定太平洋水第一次侵入大西洋的时间要早得多。与我们的结果的差异可以通过测量不同流型的不同方法来调和。像Nd这样的示踪方法对相对较小和较浅的水入侵很敏感，而远洋侵蚀机制需要强烈的深流。
The Antarctic Circumpolar Current (ACC) is a key feature of the Southern Ocean. Its development may have helped cool Antarctica and initiate Southern Hemisphere glaciation. The deep circulation of the ACC must have been established after both the Tasman gateway (between Antarctica and Australia) and the Drake Passage (between South America and Antarctica) opened. However, estimates for ACC initiation range over 20 m.y., from the middle Eocene to early Miocene. A new piston core of upper Oligocene to Holocene sediments from the South Pacific has allowed us to delimit the formation of the ACC to the late Oligocene (ca. 25–23 Ma). Upper Oligocene, current-worked sediments and a hiatus to the upper Miocene result from the beginning of the modern ACC flow; i.e., when strong currents and mixing throughout the water column were established. Previously published Nd isotope data date the first intrusion of Pacific water into the Atlantic much earlier. The discrepancy with our results can be reconciled by the different methods measuring different flow regimes. Tracer methods such as Nd are sensitive to relatively small and shallow incursions of water, whereas pelagic erosional regimes require vigorous deep flow.