Neodymium isotopic composition and concentration in the western North Atlantic Ocean: Results from the GEOTRACES GA02 section
Neodymium isotopic composition and concentration in the western North Atlantic Ocean: Results from the GEOTRACES GA02 section
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DOI：
10.1016/j.gca.2015.12.019
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发表时间：
2016-03
影响因子：
5
通讯作者：
M. Lambelet;T. Flierdt;K. Crocket;M. Rehkämper;K. Kreissig;B. Coles;M. Rijkenberg;L. Gerringa
中科院分区：
文献类型：
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作者：
M. Lambelet;T. Flierdt;K. Crocket;M. Rehkämper;K. Kreissig;B. Coles;M. Rijkenberg;L. Gerringa
海水的钕同位素组成通常被用作研究温盐环流过去变化的代用指标。然而，这种重建的现代数据库很差，对基本过程的理解也不完整。在这里，我们提出了新的观测数据Nd同位素和浓度从12个海水深度剖面，遵循北大西洋深水（NADW）的流动路径，从其形成区域在北大西洋的北方赤道大西洋。2010年，在荷兰GEOTRACES样带GA 02的北方部分进行了两次考察，期间采集了样本。结果表明，北大西洋副极地海水（NADW）的Nd同位素特征为：上拉布拉多海水（ULSW），εNd= −14.2 ± 0.3;拉布拉多海水（LSW），ε Nd = −13.7 ± 0.9;西北大西洋底层水（NWABW），εNd= −11.8 ± 1.4。在亚热带地区，这些源水混合形成NADW，并输出到全球海洋，上NADW的ε Nd值为−13.2 ± 1.0（2sd），下NADW的εNd值为−12.4 ± 0.4（2sd）。虽然这两个特征在误差范围内重叠，但由于北欧海（NWABW和NEADW）的源沃茨占主导地位，较低NADW的特征比传统使用的NADW值（εNd= −13.5）的放射性更强。浓度剖面和相应的Nd同位素剖面与其他水体性质，如盐度，硅酸盐浓度，中性密度和氯氟烃（CFC）浓度之间的比较提供了新的见解Nd的地球化学循环，并揭示了不同的过程是必要的，以考虑到所观察到的Nd特性在副极地和副热带环流和整个垂直水柱。虽然我们的数据集提供了额外的见解边界交换在沉积物再悬浮区的贡献，结果表明，在一个前所未有的水平，Nd同位素的适合性，以跟踪现代水体在强烈平流西大西洋。
The neodymium (Nd) isotopic composition of seawater is commonly used as a proxy to study past changes in the thermohaline circulation. The modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete. Here we present new observational data for Nd isotopes and concentrations from twelve seawater depth profiles, which follow the flow path of North Atlantic Deep Water (NADW) from its formation region in the North Atlantic to the northern equatorial Atlantic. Samples were collected during two cruises constituting the northern part of the Dutch GEOTRACES transect GA02 in 2010. The results show that the different water masses in the subpolar North Atlantic Ocean, which ultimately constitute NADW, have the following Nd isotope characteristics: Upper Labrador Sea Water (ULSW),εNd= −14.2 ± 0.3; Labrador Sea Water (LSW),εNd= −13.7 ± 0.9; Northeast Atlantic Deep Water (NEADW),εNd= −12.5 ± 0.6; Northwest Atlantic Bottom Water (NWABW),εNd= −11.8 ± 1.4. In the subtropics, where these source water masses have mixed to form NADW, which is exported to the global ocean, upper-NADW is characterised byεNdvalues of −13.2 ± 1.0 (2sd) and lower-NADW exhibits values ofεNd= −12.4 ± 0.4 (2sd). While both signatures overlap within error, the signature for lower-NADW is significantly more radiogenic than the traditionally used value for NADW (εNd= −13.5) due to the dominance of source waters from the Nordic Seas (NWABW and NEADW). Comparison between the concentration profiles and the corresponding Nd isotope profiles with other water mass properties such as salinity, silicate concentrations, neutral densities and chlorofluorocarbon (CFC) concentration provides novel insights into the geochemical cycle of Nd and reveals that different processes are necessary to account for the observed Nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column. While our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension, the results for open ocean seawater demonstrate, at an unprecedented level, the suitability of Nd isotopes to trace modern water masses in the strongly advecting western Atlantic Ocean.