Reversible scavenging and advection – Resolving the neodymium paradox in the South Atlantic
Reversible scavenging and advection – Resolving the neodymium paradox in the South Atlantic
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可逆清除和平流 — 解决南大西洋的钕悖论
DOI：
10.1016/j.gca.2021.09.015
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发表时间：
2021
影响因子：
5
通讯作者：
Piotrowski, Alexander M.
中科院分区：
文献类型：
--
作者：
Wang, Ruixue;Clegg, Josephine A.;Scott, Peter M.;Larkin, Christina S.;Deng, Feifei;Thomas, Alexander L.;Zheng, Xin-Yuan;Piotrowski, Alexander M.
尽管经过几十年的研究，我们对钕（Nd）和其他稀土元素（RE）的海洋循环的理解仍然存在重大差距。一个尚未得到充分解释的重要观察结果是，溶解钕的浓度通常随深度增加，类似于营养剖面，而钕同位素似乎反映了在中层和深海保守的水团混合;这被称为“钕悖论”。本文详细研究了英国GEOTRACES巡航（GA 10剖面）采集的南大西洋40°S剖面的溶解Nd同位素组成。南大西洋是我们了解海洋地球化学空间控制的一个天然实验室，因为输入的变化很大，微粒循环的空间差异，以及主要北方和南方来源的水团之间的水平平流和深度混合。这种变化也使南大西洋成为一个关键区域，受到密集的调查，旨在重建过去的变化，在海洋过程中，如生物生产力和深海circulation.Our Nd同位素的变化，从GA 10节提供的观测数据显示的水团混合和可逆清除的信号。在表层海洋（0-600米），Nd同位素组成是不同的表层洋流和空间上可以绑定到各种大陆来源。在中层洋（600-2500 m），Nd同位素垂向分布显示出不同水团水平平流的明显信号，包括大西洋或印度洋形成的北大西洋上层深水和南极中层水。Nd同位素分布还反映了可逆清除的影响，其在水柱中向下涂抹信号（即，偏移到更多的放射成因值）。在2500 m以下的深海中，Nd同位素的分布基本上遵循保守的水团混合模型。而在深海中，Nd浓度则偏离保守混合，随深度增加而不断增加。我们还观察到，Nd同位素似乎转向上覆水体的组成。这些观察结果表明，可逆清除钕到有机和其他类型的颗粒是一个主要的垂直过程中的水柱。我们还认为，这一过程可以解决由于混合动力学的钕浓度和同位素组成的解耦的“钕悖论”。由于深海水体已经有一个高的Nd浓度，从垂直过程中添加一定量的Nd的Nd同位素组成的影响，在深水质量比它的中间水体，具有相对较低的Nd浓度。
Significant gaps in our understanding of the oceanic cycling of neodymium (Nd) and the other rare earth elements (REEs) remain despite decades of research. One important observation which has not been adequately explained is that the concentration of dissolved Nd typically increases with depth, similar to nutrient profiles, while Nd isotopes appear to reflect conservative water mass mixing in the intermediate and deep ocean; this has been termed the “Nd paradox”. Here we present a detailed study of the dissolved Nd isotopic composition across a section at 40°S in the South Atlantic, collected by UK GEOTRACES cruise (section GA10). The South Atlantic represents a natural laboratory for our understanding of spatial controls on ocean geochemistry, because of the large variability of inputs, spatial differences in particulate cycling, and horizontal advection and mixing at depth between major northern- and southern-sourced water masses. This variability has also made the South Atlantic a critical region subject to intense investigations that aim at reconstructing past changes in ocean processes, such as changes in biological productivity and deep ocean circulation.Our Nd isotope results from the GA10 section provide observational data show the signal of water mass mixing and reversible scavenging. In the surface ocean (0–600 m), Nd isotopic compositions are distinct between different surface ocean currents and spatially can be tied to various continental sources. In the intermediate ocean (600–2500 m), the vertical Nd isotope distribution exhibits distinct signals of different water masses by horizontal advection, including upper North Atlantic Deep Water and Antarctic Intermediate Water formed in the Atlantic Ocean or the Indian Ocean. The Nd isotope distribution also reflects influence of reversible scavenging that smears the signals downwards in the water column (i.e., offset to more radiogenic values). In the deep ocean below 2500 m, Nd isotope distribution largely follows conservative water mass mixing model. Nd concentration in the deep ocean, however, deviates from conservative mixing and increases constantly with depth. We also observe that Nd isotopes appear to be shifted towards the composition of overlying water masses. These observations suggest that reversible scavenging of Nd onto organic and other types of particles is a major vertical process throughout the water column. We also suggest that this process can resolve the “Nd paradox” of decoupling of Nd concentration and isotopic composition due to mixing dynamics. Because abyssal water masses already have a high Nd concentration, a given amount of Nd added from the vertical process has less of an effect on Nd isotopic compositions in deep water masses than it does for intermediate water masses which have comparatively low Nd concentration.
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DOI：
--
发表时间：
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期刊：
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