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Onset of Antarctic Circumpolar Current 30 million years ago as Tasmanian Gateway aligned with westerlies

机译：塔斯马尼亚风道与西风一致，3000万年前南极绕极流的爆发

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摘要

Earth's mightiest ocean current, the Antarctic Circumpolar Current (ACC), regulates the exchange of heat and carbon between the ocean and the atmosphere(1), and influences vertical ocean structure, deep-water production(2) and the global distribution of nutrients and chemical tracers(3). The eastward-flowing ACC occupies a unique circumglobal pathway in the Southern Ocean that was enabled by the tectonic opening of key oceanic gateways during the break-up of Gondwana (for example, by the opening of the Tasmanian Gateway, which connects the Indian and Pacific oceans). Although the ACC is a key component of Earth's present and past climate system(1), the timing of the appearance of diagnostic features of the ACC (for example, low zonal gradients in water-mass tracer fields(4-7)) is poorly known and represents a fundamental gap in our understanding of Earth history. Here we show, using geophysically determined positions of continent-ocean boundaries(8), that the deep Tasmanian Gateway opened 33.5+/-1.5 million years ago (the errors indicate uncertainty in the boundary positions). Following this opening, sediments from Indian and Pacific cores recorded Pacific-type neodymium isotope ratios, revealing deep westward flow equivalent to the present-day Antarctic Slope Current. We observe onset of the ACC at around 30 million years ago, when Southern Ocean neodymium isotopes record a permanent shift to modern Indian-Atlantic ratios. Our reconstructions of ocean circulation show that massive reorganization and homogenization of Southern Ocean water masses coincided with migration of the northern margin of the Tasmanian Gateway into the mid-latitude westerly wind band, which we reconstruct at 64 degrees S, near to the northern margin. Onset of the ACC about 30 million years ago coincided with major changes in global ocean circulation(9) and probably contributed to the lower atmospheric carbon dioxide levels that appear after this time(10).
机译：地球上最强大的洋流-南极极地洋流（ACC）调节着海洋与大气之间的热量和碳的交换（1），并影响垂直海洋结构，深水生产（2）以及营养物质和营养的全球分布。化学示踪剂（3）。向东流动的ACC在南大洋中占据着独特的环流路径，这是由于冈瓦纳解体期间主要海洋通道的构造开放（例如，塔斯马尼亚通道的开放，该通道连接了印度和太平洋）而实现的。海洋）。尽管ACC是地球目前和过去气候系统的关键组成部分（1），但ACC诊断特征出现的时间（例如，水质示踪剂场中的低纬向梯度（4-7））表现不佳。众所周知，并代表了我们对地球历史理解的根本差距。在这里，我们使用地理-海洋学上确定的大陆-海洋边界位置（8）显示，塔斯马尼亚深海通道是在33.5 +/- 150万年前打开的（误差表明边界位置存在不确定性）。这次开放之后，来自印度和太平洋核心地带的沉积物记录了太平洋型钕同位素比，显示出与当今南极坡流相当的深西流。我们观察到大约在3000万年前ACC的发生，当时南大洋钕同位素记录到现代印度-大西洋比率的永久变化。我们对海洋环流的重建表明，南部海洋水团的大规模重组和均质化与塔斯马尼亚海峡北缘向中纬度西风带的迁移相吻合，我们在北纬附近以南纬64度重建了该风带。 ACC的出现大约在三千万年前，恰逢全球海洋环流发生重大变化（9），并且可能导致了这段时间之后出现的较低的大气二氧化碳水平（10）。

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  • 来源
    《Nature》 |2015年第7562期|580-583|共4页
  • 作者

    Scher Howie D.; Whittaker Joanne M.; Williams Simon E.; Latimer Jennifer C.; Kordesch Wendy E. C.; Delaney Margaret L.;

  • 作者单位

    Univ S Carolina, Dept Earth & Ocean Sci, Columbia, SC 29208 USA;

    Univ Tasmania, Inst Marine & Antarctic Studies, Hobart, Tas 7001, Australia;

    Univ Sydney, Sch Geosci, EarthByte Grp, Sydney, NSW 2006, Australia;

    Indiana State Univ, Dept Earth & Environm Syst, Terre Haute, IN 47809 USA;

    Univ Southampton, Natl Oceanog Ctr, Dept Ocean & Earth Sci, Southampton SO14 3ZH, Hants, England;

    Univ Calif Santa Cruz, Ocean Sci Dept, Santa Cruz, CA 95064 USA|Univ Calif Santa Cruz, Inst Marine Sci, Santa Cruz, CA 95064 USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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  • 正文语种 eng
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