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Particle–Seawater Interaction of Neodymium in the North Atlantic
ACS Earth and Space Chemistry ( IF 3.4 ) Pub Date : 2020-07-14 , DOI: 10.1021/acsearthspacechem.0c00034
Torben Stichel 1, 2 , Sven Kretschmer 2 , Walter Geibert 2 , Myriam Lambelet 1 , Yves Plancherel 3 , Michiel Rutgers van der Loeff 2 , Tina van de Flierdt 1
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Dissolved neodymium (Nd) isotopes (expressed as εNd) have been widely used as a water mass tracer in paleoceanography. However, one aspect of the modern biogeochemical cycle of Nd that has been sparsely investigated is the interplay between dissolved and particulate phases in seawater. We here present the first regional data set on particulate Nd isotope compositions (εNdp) and concentrations ([Nd]p) from five stations in the western North Atlantic Ocean along the GEOTRACES GA02 transect, in conjunction with previously published dissolved Nd isotope compositions (εNdd) and concentrations ([Nd]d)1. Key observations and interpretations from our new particulate data set include the following: (1) Low fractional contributions of [Nd]p to the total Nd inventory per volume unit of seawater (∼5%), with significant increases of up to 45% in benthic boundary layers. (2) Increasing Nd concentrations in suspended particulate matter ([Nd]SPM) and fractions of lithogenic material with water depth, suggesting the removal of Nd poor phases. (3) Different provenances of particulates in the subpolar and subtropical gyres as evidenced by their Nd isotope fingerprints reaching from εNdp ≈ −20 near the Labrador Basin (old continental crust), over εNdp ≈ −4 between Iceland and Greenland (young mafic provenance), to values of εNdp ≈ −13 in the subtropics (similar to African dust signal). (4) Vertical heterogeneity of εNdp as well as large deviations from ambient seawater values in the subpolar gyre indicate advection of lithogenic particles in this area. (5) Vertically homogeneous εNdp values in the subtropical gyre, indistinguishable from εNdd values, are indicative of predominance of vertical particulate supply. The process of reversible scavenging only seems to influence particulate signatures below 3 km. Overall, we do not find evidence on enhanced particle dissolution, often invoked to explain the observed increase in dissolved Nd in the North Atlantic.

中文翻译:

北大西洋钕的粒子-海水相互作用

溶解钕(Nd)的同位素(表示为ε的Nd)已经被广泛地用作在古海洋学一个水团示踪剂。然而,已被稀疏研究的Nd的现代生物地球化学循环的一个方面是海水中溶解相和颗粒相之间的相互作用。我们在这里提出对颗粒的Nd同位素组成(ε的第一个区域的数据集的Nd p)和浓度([钕] p)从沿着GEOTRACES GA02断面西部北大西洋五个站,在与先前公布的溶解的Nd同位素组合物联合(εd)和浓度([钕] d1。我们新的颗粒数据集的主要观察结果和解释如下:(1)[Nd] p对每体积单位海水中Nd总库存的贡献很小(约5%),其中显着增加了45%。底栖边界层。(2)随着水深的增加,悬浮颗粒物([Nd] SPM)和成岩物质中Nd的浓度增加,表明Nd贫相的去除。(3)所证明的通过的Nd同位素指纹从ε到达在极地微粒和亚热带环流的不同种的Nd p ≈-20附近的拉布拉多盆地(旧大陆地壳),用εp≈-4冰岛和格陵兰(年轻镁铁质出处)之间,以ε的值的Nd p ≈-13亚热带(类似于非洲灰尘信号)。(4)εNd p的垂直非均质性以及与亚极地回旋中周围海水值的较大偏差表明该地区的成岩颗粒对流。(5)垂直均匀ε的Nd p在亚热带环流值,从ε难以区分的Nd d值表示垂直颗粒供应的优势。可逆清除过程似乎只影响3 km以下的颗粒特征。总体而言,我们没有发现增加颗粒溶解的证据,经常被用来解释北大西洋中观察到的溶解Nd的增加。
更新日期:2020-09-18
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