Sources and processes affecting the distribution of dissolved Nd isotopes and concentrations in the West Pacific
Sources and processes affecting the distribution of dissolved Nd isotopes and concentrations in the West Pacific
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DOI：
10.1016/j.gca.2017.11.008
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发表时间：
2018-02-01
影响因子：
5
通讯作者：
Brumsack, Hans-Juergen
中科院分区：
文献类型：
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作者：
Behrens, Melanie K.;Pahnke, Katharina;Brumsack, Hans-Juergen
在大西洋，深层环流活跃，溶解的钕（Nd）同位素组成（表示为epsilon(Nd)）很大程度上受水团混合的控制。相比之下，以缓慢环流为特征的太平洋地区影响epsilon（Nd）分布的因素尚不清楚。太平洋地区重叠的指示是根据其毗邻的火山岛给出的。我们的研究旨在阐明不同Nd来源（河流、火山岛）、垂直（生物）地球化学过程和横向水团输送对控制韩国与斐济之间西太平洋溶解eNd和Nd浓度（[Nd]）分布的影响和相对重要性。我们发现了从韩国和中国河流到东海的非放射性成因大陆输入的迹象。在热带西太平洋，火山岛向地表水和地下水提供Nd，并将其epsilon（Nd）修改为高达+0.7的放射性成因值。这些放射性成因特征使我们能够在复杂的热带太平洋纬向流系统中详细追踪向东流动的洋流，以及与具有开放海洋太平洋epsilon（Nd）成分的西流的区分。修正的西太平洋中底水上游或本剖面内的放射性成因epsilon（Nd）也表明，由于火山岛边缘、海底脊以及与热液颗粒的边界交换，epsilon（Nd）具有非保守性。只有在开阔的西北太平洋的地下至深水（3000米）表现出epsilon（Nd）的保守行为。相反，我们发现极低（低至2.77 pmol/ kg）和横向恒定[Nd]与高盐度的南北太平洋热带水有显著的相关性，表明预形成的[Nd]是从南北太平洋亚热带环流向研究区横向输送的。这一观测结果也解释了以前在热带西太平洋观测到的低地下[Nd]。同样，南太平洋西部中部水域、南极中间水域以及南太平洋和赤道西太平洋的下环极深水在垂直和横向上几乎是不变的[Nd]，表明[Nd]的保守行为占主导地位。西北太平洋中部和中部水域的[Nd]随深度的增加而增加，反映了颗粒的Nd释放。总的来说，我们的数据表明，在西太平洋，[Nd]的分布受到主要的横向运输控制，eNd的明显非保守性改变。后者提供了热带太平洋地表和地下纬向输送的追踪，但阻止了epsilon（Nd）作为西太平洋在南纬15度至北纬28度之间主要经向循环水团的严格保守示踪剂的使用(C)。版权所有。
In the Atlantic, where deep circulation is vigorous, the dissolved neodymium (Nd) isotopic composition (expressed as epsilon(Nd)) is largely controlled by water mass mixing. In contrast, the factors influencing the epsilon(Nd) distribution in the Pacific, marked by sluggish circulation, is not clear yet. Indication for regional overprints in the Pacific is given based on its bordering volcanic islands. Our study aims to clarify the impact and relative importance of different Nd sources (rivers, volcanic islands), vertical (bio) geochemical processes and lateral water mass transport in controlling dissolved eNd and Nd concentration ([Nd]) distributions in the West Pacific between South Korea and Fiji. We find indication for unradiogenic continental input from South Korean and Chinese rivers to the East China Sea. In the tropical West Pacific, volcanic islands supply Nd to surface and subsurface waters and modify their epsilon(Nd) to radiogenic values of up to +0.7. These radiogenic signatures allow detailed tracing of currents flowing to the east and differentiation from westward currents with open ocean Pacific epsilon(Nd) composition in the complex tropical Pacific zonal current system. Modified radiogenic epsilon(Nd) of West Pacific intermediate to bottom waters upstream or within our section also indicates non-conservative behavior of epsilon(Nd) due to boundary exchange at volcanic island margins, submarine ridges, and with hydrothermal particles. Only subsurface to deep waters (3000 m) in the open Northwest Pacific show conservative behavior of epsilon(Nd). In contrast, we find a striking correlation of extremely low (down to 2.77 pmol/ kg Nd) and laterally constant [Nd] with the high-salinity North and South Pacific Tropical Water, indicating lateral transport of preformed [Nd] from the North and South Pacific subtropical gyres into the study area. This observation also explains the previously observed low subsurface [Nd] in the tropical West Pacific. Similarly, Western South Pacific Central Water, Antarctic Intermediate Water, and Lower Circumpolar Deep Water in the southern and equatorial West Pacific are marked by vertically and laterally almost invariant [Nd] indicating a dominance of conservative behavior of [Nd]. In contrast, Central and Intermediate Water in the North West Pacific are characterized by increasing [Nd] with depth reflecting Nd release from particles.Overall, our data demonstrate a dominant lateral transport control on [Nd] distributions and clear non-conservative modification of eNd in the West Pacific. The latter affords tracing of surface and subsurface zonal transport in the tropical Pacific, but prevents the use of epsilon(Nd) as strictly conservative tracer of the major meridionally circulating water masses in the West Pacific between 15 degrees S and 28 degrees N. (C) 2017 Elsevier Ltd. All rights reserved.