A major change in North Atlantic deep water circulation 1.6 million years ago
A major change in North Atlantic deep water circulation 1.6 million years ago
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160万年前北大西洋深水环流发生重大变化
DOI：
10.5194/cp-10-1441-2014
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发表时间：
2013
影响因子：
4.3
通讯作者：
M. Frank
中科院分区：
文献类型：
--
作者：
N. Khélifi;M. Frank
摘要。作为大西洋经向翻转环流（AMOC）的组成部分，全球海洋-气候系统对北欧深海溢流的形成和平流高度敏感，但其在上新世-更新世全球变冷期间的演变尚不完全清楚。特别是，在整个上新世-更新世气候转变期间，参与推动倾覆的盛行深水的来源和混合的变化没有得到很好的限制。在这里，我们研究了在过去的400万年中，AMOC向南回流的大量深溢出的演变。本文介绍了在大西洋东北部2170 ~ 5050 m水深的3个沉积物岩心（DSDP点610和ODP点980/981和900）中获得的海底放射性源钕同位素（vNd）变异的新记录。我们发现，在大约300万年前北半球主要冰期（NHG）开始之前，所有站点的vNd值主要在- 9和- 11之间振荡，这与上新世时期比今天更温暖的水团增强的垂直混合和弱分层相一致。2.7 ~ 2.0 Ma水团的vNd特征逐渐明显，表明北欧海溢流深水明显平流，与NHG增强同时发生。然而，最显著的是，在~ 1.6 Ma, 610 （2420 m水深（w.d））和980/981 （2170 m w.d）的间冰期vNd特征分别同步和永久地移动了2至3个vNd单位，减少了放射性值。此后，各测点冰期和间冰期vNd值的差异与晚第四纪相似。在900号测点（wd ~ 5050 m）的最深水团中，也记录到1.6 Ma时约2vNd单位的减少，但此后又演变为更具有放射性的值，直到现在。这种横跨1.6 Ma转变的主要vNd变化反映了东北大西洋翻转环流的重大重组，为之后更加分层的水柱和明显的水团盛行铺平了道路。
Abstract. The global ocean–climate system has been highly sensitive to the formation and advection of deep overflow water from the Nordic Seas as integral part of the Atlantic Meridional Overturning Circulation (AMOC) but its evolution over the Pliocene–Pleistocene global cooling is not fully understood. In particular, changes in the sources and mixing of prevailing deep waters that were involved in driving overturning throughout the Pliocene–Pleistocene climate transitions are not well constrained. Here we investigate the evolution of a substantial deep southward return overflow of the AMOC over the last 4 million years. We present new records of the bottom-water radiogenic neodymium isotope (vNd) variability obtained from three sediment cores (DSDP site 610 and ODP sites 980/981 and 900) at water depths between 2170 and 5050 m in the northeast Atlantic. We find that prior to the onset of major Northern Hemisphere glaciation (NHG) ∼3 million years ago (Ma), vNd values primarily oscillated between −9 and −11 at all sites, consistent with enhanced vertical mixing and weak stratification of the water masses during the warmer-than-today Pliocene period. From 2.7 Ma to ∼2.0 Ma, the vNd signatures of the water masses gradually became more distinct, which documents a significant advection of Nordic Seas overflow deep water coincident with the intensification of NHG. Most markedly, however, at ∼1.6 Ma the interglacial vNd signatures at sites 610 (2420 m water depth (w.d.)) and 980/981 (2170 m w.d.) synchronously and permanently shifted by 2 to 3 vNd units to less radiogenic values, respectively. Since then the difference between glacial and interglacial vNd values has been similar to the Late Quaternary at each site. A decrease of ∼2vNd units at 1.6 Ma was also recorded for the deepest water masses by site 900 (∼5050 m w.d.), which thereafter, however, evolved to more radiogenic values again until the present. This major vNd change across the 1.6 Ma transition reflects a significant reorganization of the overturning circulation in the northeast Atlantic paving the way for the more stratified water column with distinct water masses prevailing thereafter.
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影响因子：
5.3
作者：
T. Stichel;M. Frank;J. Rickli;B. Haley
通讯作者：
T. Stichel;M. Frank;J. Rickli;B. Haley
影响因子：
64.8
作者：
Naish, T.;Powell, R.;Williams, T.
通讯作者：
Williams, T.
上新世晚期北大西洋洋流的变化
影响因子：
5.3
作者：
Naafs B.D;Stein R;Hefter J;Khèlifi N;De Schepper S;Haug G.H.
通讯作者：
Haug G.H.
影响因子：
5.8
作者：
Crocket, K. C.;Vance, D.;Richards, D. A.
通讯作者：
Richards, D. A.