Antarctic icebergs reorganize ocean circulation during Pleistocene glacials
Antarctic icebergs reorganize ocean circulation during Pleistocene glacials
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DOI：
10.1038/s41586-020-03094-7
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发表时间：
2021-01
期刊：
影响因子：
64.8
通讯作者：
A. Starr;I. Hall;S. Barker;T. Rackow;Xu Zhang;S. Hemming;H. V. D. van der Lubbe;G. Knorr;M. Berke;G. Bigg;A. Cartagena-Sierra;F. Jiménez-Espejo;X. Gong;J. Gruetzner;N. Lathika;L. Levay;R. Robinson;M. Ziegler
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文献类型：
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作者：
A. Starr;I. Hall;S. Barker;T. Rackow;Xu Zhang;S. Hemming;H. V. D. van der Lubbe;G. Knorr;M. Berke;G. Bigg;A. Cartagena-Sierra;F. Jiménez-Espejo;X. Gong;J. Gruetzner;N. Lathika;L. Levay;R. Robinson;M. Ziegler
现代海洋大尺度传质的主要特征是大西洋经向翻转环流（AMOC）。这种环流的几何形状和强度在不同的时间尺度上影响着全球气候。古海洋学证据表明，在过去150万年的冰期，AMOC的特征与今天明显不同；在大西洋盆地，南大洋深水的体积增加，而北大西洋深水的核心（NADW）在其上方变浅。缺乏关于这一现象起源的证据意味着导致全球冰川条件的事件顺序仍然不清楚。在这里，我们提出了多个代理证据，表明在更新世时期，印度洋-大西洋南大洋（0-50°E）的南极冰山融化向北移动系统地早于深水块体重组一至两千年。借助冰山轨迹模型实验，我们证明了冰川时期冰山轨迹的这种变化可能导致南大洋淡水的大量重新分配。我们认为，这与海冰覆盖的增加相一致，使正浮力异常“逃逸”到AMOC的上肢，提供了南大洋表面条件与NADW形成之间的遥相关。这一机制的强度和速度在中更新世的转变过程中发生了很大的变化，同时“南向逸出”强度的增加和深部环流扰动表明，这一机制是向“100-kyr世界”过渡的关键反馈，在“100-kyr世界”中，冰期-间冰期旋回大约每10万年发生一次。
The dominant feature of large-scale mass transfer in the modern ocean is the Atlantic meridional overturning circulation (AMOC). The geometry and vigour of this circulation influences global climate on various timescales. Palaeoceanographic evidence suggests that during glacial periods of the past 1.5 million years the AMOC had markedly different features from today; in the Atlantic basin, deep waters of Southern Ocean origin increased in volume while above them the core of the North Atlantic Deep Water (NADW) shoaled. An absence of evidence on the origin of this phenomenon means that the sequence of events leading to global glacial conditions remains unclear. Here we present multi-proxy evidence showing that northward shifts in Antarctic iceberg melt in the Indian–Atlantic Southern Ocean (0–50° E) systematically preceded deep-water mass reorganizations by one to two thousand years during Pleistocene-era glaciations. With the aid of iceberg-trajectory model experiments, we demonstrate that such a shift in iceberg trajectories during glacial periods can result in a considerable redistribution of freshwater in the Southern Ocean. We suggest that this, in concert with increased sea-ice cover, enabled positive buoyancy anomalies to ‘escape’ into the upper limb of the AMOC, providing a teleconnection between surface Southern Ocean conditions and the formation of NADW. The magnitude and pacing of this mechanism evolved substantially across the mid-Pleistocene transition, and the coeval increase in magnitude of the ‘southern escape’ and deep circulation perturbations implicate this mechanism as a key feedback in the transition to the ‘100-kyr world’, in which glacial–interglacial cycles occur at roughly 100,000-year periods.