The global ocean overturning circulation is a major means of distributing heat around the Earth, and an important trigger or amplifier of climate change. This study presents a 1.5-Myr-long neodymium (Nd) isotope record of Deep Sea Drilling Project Site 607, in the core of present-day North Atlantic Deep Water (NADW), the water mass that drives the overturning circulation and its Atlantic end-member (Broecker, 1991; Gordon, 1991), in order to document its composition through time. This time interval is marked by major changes in fundamental aspects of the Earth's climate, including the Mid-Pleistocene Transition (MPT) from ∼41-kyr to ∼100-kyr interglacial-glacial cycles and more intense glacials. The new record, mainly focusing on interglacial and glacial peaks, shows a pattern that mimics the record of benthic foraminiferal δ¹⁸O (Lisiecki and Raymo, 2005) in that the magnitude of interglacial-glacial Nd isotope shifts were smaller in the 41-kyr world than in the 100-kyr world. During the “900 ka event” (Clark et al., 2006), between ∼960 and 860 ka, marking the first 100-kyr interglacial-glacial cycle, the Nd isotope ratios shift abruptly to higher values, consistent with increased incursion of Southern Ocean water masses into the deep North Atlantic. This pattern was previously observed in the South Atlantic over the same time interval and interpreted as a weakened presence of NADW signal that reflected a period of disrupted deep ocean overturning circulation, termed the “MPT-AMOC crisis” (Pena and Goldstein, 2014). The Site 607 data support this interpretation and show the effects to be basin-wide. Following the disruption, an enhanced southern-sourced Nd isotope signature remained for ∼200 kyr during the period of “lukewarm interglacials” (Howe and Piotrowski, 2017; Jaccard et al., 2013), consistent with weaker overturning circulation. With the exception of this “MPT-AMOC crisis and recovery” interval, the Nd isotope ratios during interglacial peaks have been similar to present-day NADW, indicating similar interglacial North Atlantic ocean circulation dynamics both before and after the MPT. This contrasts with the pattern during glacial periods of the 100-kyr world, during which Nd isotopes have continued to follow the pattern of the 900-kyr event indicating a strong southern water mass signal, interpreted as intensified incursions of Southern Ocean water into the deep North Atlantic and consistent with a generally weaker overturning circulation during glacials.

全球海洋翻转环流是地球周围热量分布的主要方式，是气候变化的重要触发或放大器。这项研究展示了深海钻探项目站点 607的 1.5 Myr 长钕(Nd)同位素记录，该站点位于当今北大西洋深水(NADW) 的核心，该水团驱动翻转环流及其大西洋末端-member (Broecker, 1991; Gordon, 1991)，以便记录其随时间的构成。这个时间间隔的标志是地球气候基本方面的重大变化，包括中更新世过渡期(MPT)从~41-kyr 到~100-kyr 间冰期-冰期循环和更强烈的冰期。新记录主要集中在间冰期和冰期峰，显示出一种模式，模仿底栖有孔虫 δ ¹⁸ O的记录（Lisiecki 和 Raymo，2005 年），因为间冰期 - 冰期 Nd 同位素位移的幅度在 41-kyr 中较小世界比在 100-kyr 世界中。“ 900 ka”活动期间”（克拉克等人，2006 年），在 ~960 到 860 ka 之间，标志着第一个 100 kyr 间冰期 - 冰期循环，Nd 同位素比率突然转变为更高的值，与南大洋水团侵入深部的增加一致北大西洋。这种模式先前在同一时间间隔内在南大西洋观察到，并被解释为 NADW 信号减弱，反映了一段被称为“ MPT-AMOC 危机”的深海翻转环流中断期（Pena 和 Goldstein，2014 年）。Site 607 数据支持这种解释，并显示出整个盆地的影响。中断之后，在“冷暖间冰期”期间，源自南方的 Nd 同位素特征增强了约 200 kyr”（Howe 和 Piotrowski，2017 年；Jaccard 等人，2013 年），与较弱的翻转环流一致。除了这个“MPT-AMOC危机和恢复”区间外，间冰期峰值期间的Nd同位素比率与当今的NADW相似，表明MPT前后的间冰期北大西洋环流动力学相似。这与 100-kyr 世界冰河时期的模式形成对比，在此期间，Nd 同位素继续遵循 900-kyr 事件的模式，表明强烈的南部水团信号，被解释为南大洋水加强侵入深海北大西洋与冰川期普遍较弱的翻转环流相一致。