Extreme deepening of the Atlantic overturning circulation during deglaciation
Extreme deepening of the Atlantic overturning circulation during deglaciation
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DOI：
10.1038/ngeo921
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发表时间：
2010-08-01
影响因子：
18.3
通讯作者：
Skinner, Luke C.
中科院分区：
文献类型：
--
作者：
Barker, Stephen;Knorr, Gregor;Skinner, Luke C.
晚更新世时期的冰川终止与日照的变化有关。它们还不时受到千年尺度气候变化的影响，其特点是大西洋纬向翻转环流的减弱和随后的加强。这种普遍存在的关联表明，这些振荡可能是冰川消退的必要组成部分。模式模拟表明，在这些终端振荡期间，环流减弱的时期之后，环流将在其恢复时过冲，但这种现象尚未观察到。在这里，我们使用底栖有孔虫和碳酸盐保存指数的放射性碳测量重建通风在过去的40,000年在南大西洋深处的变化。我们发现的证据，一个特别深的扩张大西洋翻转细胞直接弱模式与海因里希体育场1。我们的海洋环流模式模拟的分析表明，北大西洋深水出口扩张期间大于间冰期条件。我们在38，000年前的Dansgaard-Oeschger Interstadial Event 8中发现了类似的深度扩张，该事件发生在Heinrich Stadial 4之后。我们的结论是，大气中CO2浓度的上升和由此产生的变暖与一个特别弱的翻转环流足以触发切换到一个强大的循环，但间冰期条件的完全过渡需要额外的强迫在轨道尺度。
Glacial terminations during the late Pleistocene epoch are associated with changes in insolation. They are also punctuated by millennial-scale climate shifts, characterized by a weakening and subsequent strengthening of the Atlantic meridional overturning circulation. This ubiquitous association suggests that these oscillations may be a necessary component of deglaciation. Model simulations have suggested that the period of weakened circulation during these terminal oscillations would be followed by an overshoot of the circulation on its resumption, but this phenomenon has not yet been observed. Here we use radiocarbon measurements of benthic foraminifera and carbonate preservation indices to reconstruct ventilation changes in the deep South Atlantic Ocean over the past 40,000 years. We find evidence for a particularly deep expansion of the Atlantic overturning cell directly following the weak mode associated with Heinrich Stadial 1. Our analysis of an ocean general circulation model simulation suggests that North Atlantic Deep Water export during the expansion was greater than that of interglacial conditions. We find a similar deep expansion duringDansgaard-Oeschger Interstadial Event 8, 38,000 years ago, which followed Heinrich Stadial 4. We conclude that the rise in atmospheric CO2 concentrations and resultant warming associated with an especially weak overturning circulation are sufficient to trigger a switch to a vigorous circulation, but a full transition to interglacial conditions requires additional forcing at an orbital scale.