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Antarctic icebergs reorganize ocean circulation during Pleistocene glacials
Nature ( IF 42.778 ) Pub Date : 2021-01-13 , DOI: 10.1038/s41586-020-03094-7
Aidan Starr; Ian R. Hall; Stephen Barker; Thomas Rackow; Xu Zhang; Sidney R. Hemming; H. J. L. van der Lubbe; Gregor Knorr; Melissa A. Berke; Grant R. Bigg; Alejandra Cartagena-Sierra; Francisco J. Jiménez-Espejo; Xun Gong; Jens Gruetzner; Nambiyathodi Lathika; Leah J. LeVay; Rebecca S. Robinson; Martin Ziegler

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 today1; 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) shoaled2. 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.



中文翻译:

更新世冰川期间南极冰山重新组织海洋循环

现代海洋中大规模传质的主要特征是大西洋经向翻转环流(AMOC)。这种循环的几何形状和活力在不同的时间尺度上影响全球气候。古海洋学证据表明,在过去150万年的冰川时期,AMOC与今天的冰川特征明显不同1 ; 在大西洋盆地,起源于南大洋的深水的数量增加,而在其上方的北大西洋深水(NADW)的核心被浅埋2。缺乏关于这种现象起源的证据意味着导致全球冰川状况的事件序列仍然不清楚。在这里,我们提供了多种代理证据,表明在更新世时代的冰期期间,印度-大西洋南部海洋(0-50°E)南极冰山融化的北移系统地将深水物质重组提前了一到两千年。借助冰山轨迹模型实验,我们证明了冰川期冰山轨迹的这种变化会导致南大洋的淡水大量重新分配。我们建议,这与海冰覆盖面积的增加相结合,可使正浮力异常“逃逸”到AMOC的上肢,在南大洋表面状况与NADW的形成之间提供遥远的联系。该机制的幅度和步调在整个更新世中期都发生了演变,同时,“南方逃逸”和深度循环扰动的同期增加表明该机制是过渡到“ 100世纪世界”的关键反馈,其中冰期至冰期间周期大约发生在100,000年。

更新日期:2021-01-13
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