Barium in deep-sea bamboo corals: Phase associations, barium stable isotopes, & prospects for paleoceanography
Barium in deep-sea bamboo corals: Phase associations, barium stable isotopes, & prospects for paleoceanography
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DOI：
10.1016/j.epsl.2019.115751
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发表时间：
2019-11-01
影响因子：
5.3
通讯作者：
Horner, Tristan J.
中科院分区：
文献类型：
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作者：
Geyman, Ben M.;Ptacek, Jamie L.;Horner, Tristan J.
重建过去的海水三角洲(138)/Ba-134(NIST)（钡同位素组成）可以补充现有的水团物源和深海环流指标。深海竹珊瑚具有独特的记录Ba同位素变化的能力，因为它们在海洋中的分布非常广泛，并且与周围海水中的Ba含量大致成比例。然而，利用这些记录需要知道：深海珊瑚骨骼中含有Ba的相，标本忠实地捕捉了现代Ba同位素化学，以及骨骼内部的变化主要与周围海水成分的历史变化有关。我们通过阶式清洗实验，对八个从加利福尼亚边缘（870- 2055米）采集的活体标本与环境海水进行“核心-顶部”比较，并分别通过检查骨骼Ba化学的历史变异性来研究这些要求。首先，我们报告了非碳酸盐相对竹珊瑚Ba/Ca的贡献最小，从而避免了对活体标本进行化学清洗的需要。其次，利用新获得的东北太平洋ba同位素化学剖面，我们观察到竹珊瑚忠实地反映了环境海水的ba同位素偏移量，δ (138)/Ba-134（珊瑚- sw）为-0.37 +/- 0.03 ppm （+/- 2 SD, n = 8）。Ba的分配系数K-D（Ba）对分类同样不敏感，但随深度线性降低。驱动机制尚不清楚。第三，我们发现在过去一个世纪的历史生长中Ba/Ca和Ba同位素变化最小。我们将这种不变性解释为深海竹珊瑚在其漫长的生命周期中对环境Ba化学的整体保真度。Delta(138)/Ba-134（珊瑚- sw）对环境梯度的不敏感表明竹珊瑚的ba同位素组成可以单独用海水组成来解释，这应该在一系列时间尺度上的海洋环流研究中找到无数的应用。(C) 2019 Elsevier B.V.版权所有
Reconstruction of past seawater delta(138)/Ba-134(NIST) (barium-isotopic compositions) can augment existing proxies of water mass provenance and deep-ocean circulation. Deep-sea bamboo corals are uniquely poised to record Ba-isotopic variations, given their widespread oceanographic distribution and incorporation of ambient Ba in approximate proportion to that in surrounding seawater. However, the utility of such records requires knowing: the phases hosting Ba in deep-sea coral skeletons, that specimens faithfully capture modern Ba-isotopic chemistry, and that internal skeletal variability relates principally to historical variations in the composition of ambient seawater. We investigated each of these requirements using a stepped cleaning experiment, a 'core-top' comparison of eight live-collected specimens from the California margin (870-2,055 m) against ambient seawater, and through examination of historical variability in skeletal Ba chemistry, respectively. First, we report that non-carbonate phases minimally contribute to bamboo coral Ba/Ca, obviating the need for chemical cleaning of live-collected specimens. Second, using newly-obtained profiles of northeast Pacific Ba-isotopic chemistry, we observe that bamboo corals faithfully reflect ambient seawater with a taxonomically- and environmentally-invariant Ba-isotopic offset, Delta(138)/Ba-134(coral-SW), of -0.37 +/- 0.03 parts per thousand (+/- 2 SD, n = 8). The partition coefficient for Ba, K-D(Ba), is similarly insensitive to taxonomy, but linearly decreases with depth. The driving mechanism is unresolved. Third, we find minimal Ba/Ca and Ba-isotopic variability in historical growth representing the past century. We interpret this invariance as evidencing the overall fidelity of deep-sea bamboo corals for ambient Ba chemistry over their long lifespans. The insensitivity of Delta(138)/Ba-134(coral-SW) to environmental gradients indicates that the Ba-isotopic composition of bamboo corals can be solely interpreted in terms of seawater composition, which should find myriad applications to the study of past ocean circulation over a range of timescales. (C) 2019 Elsevier B.V. All rights reserved.