Crystal fabrics and element impurities (Sr/Ca, Mg/Ca, and Ba/Ca) in shells of Arctica islandica—Implications for paleoclimate reconstructions
Crystal fabrics and element impurities (Sr/Ca, Mg/Ca, and Ba/Ca) in shells of Arctica islandica—Implications for paleoclimate reconstructions
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DOI：
10.1016/j.palaeo.2011.05.013
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发表时间：
2013-03
期刊：
影响因子：
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通讯作者：
B. Schöne;P. Radermacher;Zengjie Zhang;Dorrit E. Jacob-
中科院分区：
文献类型：
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作者：
B. Schöne;P. Radermacher;Zengjie Zhang;Dorrit E. Jacob-
Sr/Ca、Mg/Ca和Ba/Ca值在Arctica islandica贝壳中分布不均匀。这些图案在很大程度上与晶体结构（晶体的尺寸、习性和取向）或控制它们的过程有关。外壳层（oOSL;均匀和不规则的简单棱柱形晶体织物）的外子层含有比内子层（iOSL;交叉针状，交叉层状，精细交叉层状和不规则的简单棱柱形晶体织物）高62%的元素/Ca值。Sr/Ca和Mg/Ca值从oOSL的外部向oOSL/iOSL过渡区逐渐减小。这种化学位移伴随着从均匀的晶体织物逐渐过渡到交叉层状/针状晶体织物。年生长线附近（不规则简单棱柱），即，在缓慢生长期间，由于Sr/Ca和Mg/Ca值接近海水的典型值，Sr和Mg似乎与周围环境平衡地沉积。在生长季节的剩余时间，Sr/Ca和Mg/Ca仍然远远低于预期的热力学平衡值。然而，Ba/Ca峰值在一年中的不同时间不规则地发生，晶体结构没有任何明显的变化。可能的是，这些峰中所含的环境信息不像Sr和Mg那样受到重要影响的严重过滤。本研究的结果可以帮助开发新的技术，提取环境信号的双壳类贝壳的金属钙比。
Sr/Ca, Mg/Ca and Ba/Ca values are heterogeneously distributed in shells of Arctica islandica. These patterns are largely associated with crystal fabrics (size, habit and orientation of crystals) or the processes controlling them. The outer sublayer of the outer shell layer (oOSL; homogenous and irregular simple prismatic crystal fabrics,) contained element/Ca values up to 62% higher than the inner sublayer (iOSL; crossed-acicular, crossed-lamellar, fine crossed-lamellar and irregular simple prismatic crystal fabrics). A gradual decrease in Sr/Ca and Mg/Ca values was observed from the outer portions of the oOSL toward the oOSL/iOSL transition zone. This chemical shift was accompanied by a gradual transition from homogenous crystal fabrics into crossed-lamellar/acicular crystal fabrics. Near annual growth lines (irregular simple prisms), i.e., during periods of slow growth, Sr and Mg seemed to be deposited in equilibrium with the ambient environment because the Sr/Ca and Mg/Ca values approached values typical for seawater. During the remainder of the growing season, Sr/Ca and Mg/Ca remained far below values expected for thermodynamic equilibrium. Ba/Ca peaks, however, occurred erratically at different times of the year without any noticeable changes in crystal fabrics. Likely, the environmental information contained in these peaks was less severely filtered by vital effects than in Sr and Mg. The findings of the present study can help to develop new techniques with which extract environmental signals from the metal-to-calcium ratios of bivalve shells.