Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA.
Earth System Science Department, 3200 Croul Hall, University of California, Irvine, California 92697-3100, USA.
Nature. 2014 Jul 3;511(7507):75-8. doi: 10.1038/nature13472.
Several large and rapid changes in atmospheric temperature and the partial pressure of carbon dioxide in the atmosphere--probably linked to changes in deep ocean circulation--occurred during the last deglaciation. The abrupt temperature rise in the Northern Hemisphere and the restart of the Atlantic meridional overturning circulation at the start of the Bølling-Allerød interstadial, 14,700 years ago, are among the most dramatic deglacial events, but their underlying physical causes are not known. Here we show that the release of heat from warm waters in the deep North Atlantic Ocean probably triggered the Bølling-Allerød warming and reinvigoration of the Atlantic meridional overturning circulation. Our results are based on coupled radiocarbon and uranium-series dates, along with clumped isotope temperature estimates, from water column profiles of fossil deep-sea corals in a limited area of the western North Atlantic. We find that during Heinrich stadial 1 (the cool period immediately before the Bølling-Allerød interstadial), the deep ocean was about three degrees Celsius warmer than shallower waters above. This reversal of the ocean's usual thermal stratification pre-dates the Bølling-Allerød warming and must have been associated with increased salinity at depth to preserve the static stability of the water column. The depleted radiocarbon content of the warm and salty water mass implies a long-term disconnect from rapid surface exchanges, and, although uncertainties remain, is most consistent with a Southern Ocean source. The Heinrich stadial 1 ocean profile is distinct from the modern water column, that for the Last Glacial Maximum and that for the Younger Dryas, suggesting that the patterns we observe are a unique feature of the deglacial climate system. Our observations indicate that the deep ocean influenced dramatic Northern Hemisphere warming by storing heat at depth that preconditioned the system for a subsequent abrupt overturning event during the Bølling-Allerød interstadial.
在末次冰消期，大气温度和大气二氧化碳分压发生了几次较大的快速变化，这些变化可能与深海环流的变化有关。在 14700 年前的博林-阿勒罗德间冰期，北半球的突然升温以及大西洋经向翻转环流的重新启动，是末次冰消期中最显著的事件之一，但它们的潜在物理原因尚不清楚。在这里，我们表明北大西洋深部温暖水域释放的热量可能引发了博林-阿勒罗德变暖，并重新激发了大西洋经向翻转环流。我们的研究结果基于放射性碳和铀系列日期，以及从北大西洋西部有限区域的化石深海珊瑚水柱剖面获得的凝聚同位素温度估计。我们发现，在 Heinrich 冰期 1 期间（博林-阿勒罗德间冰期之前的凉爽时期），深海比浅水区温暖约 3 摄氏度。这种海洋通常的热分层的逆转发生在博林-阿勒罗德变暖之前，一定与深海中的盐度增加有关，以保持水柱的静态稳定性。温暖而咸水团的放射性碳含量的消耗意味着与快速的表面交换长期脱节，尽管存在不确定性，但最符合南大洋的来源。Heinrich 冰期 1 的海洋剖面与现代水柱、末次冰期最大值和新仙女木期的海洋剖面明显不同，这表明我们观察到的模式是冰消期气候系统的一个独特特征。我们的观测表明，深海通过在深部储存热量来影响北半球的急剧变暖，为随后在博林-阿勒罗德间冰期发生的突然翻转事件做好了准备。
