Extracting foraminiferal seawater Nd isotope signatures from bulk deep sea sediment by chemical leaching
Extracting foraminiferal seawater Nd isotope signatures from bulk deep sea sediment by chemical leaching
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DOI：
10.1016/j.chemgeo.2016.06.024
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发表时间：
2016-11-07
期刊：
影响因子：
3.9
通讯作者：
Frank, Martin
中科院分区：
文献类型：
--
作者：
Blaser, Patrick;Lippold, Jorg;Frank, Martin
海水放射性钕（Nd-143/Nd-144）同位素特征是重建过去深水物源的宝贵工具。沉积有孔虫或鱼的牙齿是最可靠的档案已知的钕同位素为基础的重建过去的海水。由于这些档案的分布和保存是有限的，从散装沉积物中提取水成铁锰羟基氧化物提供了一个容易适用的替代方案。然而，这种方法意味着由于在提取过程中可能释放非海水来源的Nd而产生伪影的风险。在这里，我们重新审视和进一步调查的可靠性提取海水来源的Nd同位素签名通过浸出散装深海沉积物与两种常用的缓冲乙酸和酸还原混合溶液。重复应用这种逐步沥滤程序，以不同的非脱碳沉积物从不同的设置在大西洋深处显示出显着的元素和Nd同位素的趋势，在实验室的沥滤过程中。我们的研究结果表明，海水Nd同位素组成的提取与碳酸盐和锰的氧化物只有在开始的浸出系列。在化学提取过程中，碳酸盐有效地起到缓冲作用，防止酸引起的铁氧化物和火山物质的活动。一旦这个缓冲区被消耗，潜在的火山成因阶段受到相当大的攻击，导致在提取的Nd同位素信号的变化高达+12单位。这样的火山相是一个显着的污染物Nd的来源，反映了显着升高的Al/Nd签名。因此，我们提出了一个修订后的弱浸出协议碳酸盐含深海沉积物，这是简单的使用，提供了良好的协议与未清洁有孔虫获得的数据，并可以很容易地筛选污染。(C)2016爱思唯尔B. V.保留所有权利。
The seawater radiogenic neodymium (Nd-143/Nd-144) isotope signature is an invaluable tool for the reconstruction of past deep water provenance. Sedimentary foraminifera or fish teeth are among the most reliable archives known for Nd isotope based reconstructions of past seawater. As the distribution and preservation of these archives are limited, the extraction of hydrogenetic ferromanganese oxyhydroxides from bulk sediments provide an easily applicable alternative. This method, however, implies the risk of generating artefacts due to the possible release of non-seawater derived Nd during the extraction procedure. Here we revisit and further investigate the reliability of the extraction of seawater derived Nd isotope signatures via leaching of bulk deep sea sediments with two commonly used buffered acetic acid and acid-reductive mix solutions. Repeated application of such stepwise leaching procedures to different non-decarbonated sediments from distinct settings across the deep Atlantic Ocean shows pronounced elemental and Nd isotope trends during the leaching process in the laboratory. Our results show that seawater Nd isotope compositions are extracted together with carbonates and manganese oxides only at the beginning of the leaching series. During chemical extraction, the carbonates effectively work as a buffer preventing acid-induced mobilisation of Fe oxides and volcanogenic material. Once this buffer is consumed, potentially present volcanogenic phases are considerably attacked, leading to shifts in the extracted Nd isotope signal of up to +12 epsilon units. Such volcanogenic phases are a significant source of contaminant Nd reflected by markedly elevated Al/Nd signatures. We consequently propose a revised weak leaching protocol for carbonate bearing deep sea sediments, which is simple to use, provides excellent agreement with data obtained from uncleaned foraminifera, and can be easily screened for contamination. (C) 2016 Elsevier B.V. All rights reserved.