Neodymium isotopic evidence for linked changes in Southeast Atlantic and Southwest Pacific circulation over the last 200 kyr
Neodymium isotopic evidence for linked changes in Southeast Atlantic and Southwest Pacific circulation over the last 200 kyr
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DOI：
10.1016/j.epsl.2016.09.027
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发表时间：
2016-12
影响因子：
5.3
通讯作者：
R. Hu;T. Noble;A. Piotrowski;I. N. McCave;H. Bostock;H. Neil
中科院分区：
文献类型：
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作者：
R. Hu;T. Noble;A. Piotrowski;I. N. McCave;H. Bostock;H. Neil
对深翻转环流的几何形状和强度的了解是理解冰期-间冰期(G-I)时间尺度上过去气候变化的核心。利用浮游有孔虫的钕(ND)同位素比值，从5个沉积岩心重建了东南大西洋和西南太平洋过去200KYR以来的水团来源和中、深层水的混合史。大西洋东南部岩心深度断面的Nd同位素在末次盛冰期显示了较强的地球化学梯度，在该边界以下的εNd值为∼−6.0，高于该边界以上的∼−7.8。相反，在全新世的中层和深部都观察到了类似的εNd值(∼−9.5)。冰川上层海洋的辐射成因比下层海洋低1.8NdUnits，反映了东南大西洋上层北大西洋成分水(NACW)的增加。在东南大西洋和西南太平洋中、深水观测到了相干的Nd同位素变化，在海洋同位素阶段2、4和6主要漂移到更具放射性的εNd值。这表明在寒冷的海洋阶段，NACW向南大洋的通量减少，可能伴随着水团几何结构的变化。东南大西洋和西南太平洋中间水之间的2εNd单位的恒定偏移量表明，在上一个冰川周期中，辐射成因较弱的NACW持续传播到上太平洋。此外，东南大西洋和西南太平洋中水和深水之间较大的冰川垂直εNd梯度表明，NACW带入深海的比例减少，这与提出上、下经向翻转单元之间混合减少的研究一致。
Knowledge of the geometry and strength of the deep overturning circulation is central to the understanding of past climate variability on glacial–interglacial (G–I) timescales. In this study, neodymium (Nd) isotopic ratios on planktonic foraminifera are used to reconstruct the water mass source and mixing history of intermediate and deep water in the Southeast (SE) Atlantic and Southwest (SW) Pacific over the past 200 kyr from five sediment cores. Nd isotopes from a depth transect of cores in the SE Atlantic displayed a stronger geochemical gradient around 3.5 km at the LGM, with higherεNdvalues of ∼−6.0 below that boundary than those of ∼−7.8 above. In contrast, a similarεNdvalue (∼−9.5) is observed at both the intermediate and abyssal depths in the Holocene. The glacial upper ocean is 1.8εNdunits less radiogenic than the lower ocean, reflecting an increase in the amount of North Atlantic Component Water (NACW) in the upper SE Atlantic. A coherent Nd isotope change was observed in the SE Atlantic and SW Pacific intermediate and deep water with major excursion to more radiogenicεNdvalues during Marine Isotope Stage (MIS) 2, 4 and 6. This suggests the flux of NACW to the Southern Ocean was reduced during cold marine stages, possibly accompanied by changes in the water mass geometry. The constant 2εNd-unit offset between intermediate water in the SE Atlantic and SW Pacific suggests the persistent propagation of less radiogenic NACW to the upper Pacific Ocean over the last glacial cycle. Moreover, the larger glacial verticalεNdgradients between the intermediate and deep waters in both the SE Atlantic and SW Pacific indicate a decreased proportion of NACW entrainment into the deep oceans, consistent with studies proposing reduced mixing between the upper and lower meridional overturning cells.