Preferential Loss of High Trace Element Bearing Inner Calcite in Foraminifera During Physical and Chemical Cleaning
Preferential Loss of High Trace Element Bearing Inner Calcite in Foraminifera During Physical and Chemical Cleaning
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DOI：
10.1029/2020gc009419
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发表时间：
2021-01-01
影响因子：
3.5
通讯作者：
Fehrenbacher, Jennifer
中科院分区：
文献类型：
--
作者：
Fritz-Endres, Theresa;Fehrenbacher, Jennifer
有孔虫方解石壳中的微量元素在古海洋学研究中有着广泛的应用。几乎所有TE分析协议都包括清洁以去除污染物相。了解TE成分在物理和化学清洗过程中是如何改变的，对于确保古气候重建的准确性至关重要。假设Ba/Ca和Mn/Ca比值升高是由于成岩作用叠加造成的，则通常使用包括腐蚀性试剂的侵蚀性清洗步骤来清洗Ba/Ca和Mn/Ca比值升高的壳体。我们提供的证据表明，升高的壳内Ba/Ca，Mn/Ca和Zn/Ca比值是晶格束缚的，并在非棘物种Neogloboquadrina dutertrei和Pulleniatina pullenioculata钙化过程中纳入内部方解石的主要信号。我们首先证明，使用激光烧蚀深度剖析分析，积极的清洁后，传统上用于消除锰和钡污染的完整的清洁协议，优先删除内部（个体发育）方解石和有利于低Ba/Ca，Mn/Ca，Zn/Ca，Mg/Ca地壳/皮质方解石。在一个单独的实验中，我们表明，机械破碎的散装壳制备的解决方案分析也优先去除内方解石，有利于低TE地壳/皮质方解石。在N中，个体发育方解石的优先损失使Ba/Ca、Mn/Ca和Zn/Ca比值降低了50%-90%。dutertrei和P.这使有孔虫TE结果偏向较低的值，并可能产生对解释下钻芯记录有问题的数据。
Trace elements (TEs) in the calcite shells of foraminifera are widely used in paleoceanographic reconstructions. Nearly all TE analytical protocols include cleaning to remove contaminant phases. Understanding, how the TE composition is altered during physical and chemical cleaning is of utmost importance in ensuring the accuracy of paleoclimate reconstructions. Aggressive cleaning steps that include corrosive reagents are commonly used to clean shells with elevated Ba/Ca and Mn/Ca ratios, under the assumption that these elements are elevated due to diagenetic overprinting. We provide evidence that elevated intrashell Ba/Ca, Mn/Ca, and Zn/Ca ratios are lattice bound and a primary signal incorporated into inner calcite during calcification in the nonspinose species Neogloboquadrina dutertrei and Pulleniatina obliquiloculata. We first demonstrate, using laser ablation depth profiling analyses, that aggressive cleaning following the full cleaning protocol traditionally used to eliminate Mn and Ba contamination, preferentially removes inner (ontogenic) calcite and favors the low Ba/Ca, Mn/Ca, Zn/Ca, and Mg/Ca crust/cortex calcite. In a separate experiment, we demonstrate that mechanical fragmentation of bulk shells prepared for solution analysis also preferentially removes inner calcite and favors the low TE crust/cortex calcite. Preferential loss of the ontogenic calcite decreases Ba/Ca, Mn/Ca, and Zn/Ca ratios by 50%-90% in N. dutertrei and P. obliquiloculata shells. This biases foraminiferal TE results toward lower values and may yield data that is problematic for the interpretation of downcore records.