Profiling planktonic foraminiferal crust formation
Profiling planktonic foraminiferal crust formation
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DOI：
10.1002/2015gc005752
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发表时间：
2015-07
期刊：
影响因子：
3.7
通讯作者：
J. Steinhardt;L. D. de Nooijer;G. Brummer;G. Reichart
中科院分区：
文献类型：
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作者：
J. Steinhardt;L. D. de Nooijer;G. Brummer;G. Reichart
浮游有孔虫一生中在水柱中垂直迁移，因此在一系列与深度相关的条件下生长和钙化。一些物种在生命周期结束时形成方解石饰面、外壳或皮层。这个额外的方解石层可能在结构、组成和厚度上有所不同，可能占其总壳质量的大部分，从而主导整个壳的元素和同位素特征。在这里，我们应用激光烧蚀ICP - MS深度剖面来评估来自沉积物圈闭的三种壳层物种的壳壁厚度和Mg/Ca组成的变化。在组成上，Neogloboquadrina dutrei和Globorotalia scitula的地壳以及Pulleniatina obliquiloculata的皮层中Mg/Ca的含量明显较低，与它们的层状方解石壳的物种特异性Mg/Ca无关。无论初始壳壁厚度如何，两种甲壳物种的壳壁厚度均占总厚度的近一半，而皮质物种的壳壁厚度占总厚度的近三分之一。地壳厚度和Mg/Ca值向较年轻的室减小，而在G. scitula中也有较小程度的减小。相比之下，斜丘木的皮层厚度几乎恒定，Mg/Ca通过整个室壁均匀分布。地壳的厚度和镁钙比值表明温度不是控制地壳形成的主要因素。相反，我们提出了一个深度分辨率模型来解释个体内部和连续腔室之间的成分差异，以及在这里研究的所有三个物种中地壳和层状方解石的成分异质性。
Planktonic foraminifera migrate vertically through the water column during their life, thereby growing and calcifying over a range of depth‐associated conditions. Some species form a calcite veneer, crust, or cortex at the end of their lifecycle. This additional calcite layer may vary in structure, composition, and thickness, potentially accounting for most of their total shell mass and thereby dominating the element and isotope signature of the whole shell. Here we apply laser ablation ICP‐MS depth profiling to assess variability in thickness and Mg/Ca composition of shell walls of three encrusting species derived from sediment traps. Compositionally, Mg/Ca is significantly lower in the crusts of Neogloboquadrina dutertrei and Globorotalia scitula, as well as in the cortex of Pulleniatina obliquiloculata, independent of the species‐specific Mg/Ca of their lamellar calcite shell. Wall thickness accounts for nearly half of the total thickness in both crustal species and nearly a third in cortical P. obliquiloculata, regardless of their initial shell wall thickness. Crust thickness and crustal Mg/Ca decreases toward the younger chambers in N. dutertrei and to a lesser extent, also in G. scitula. In contrast, the cortex of P. obliquiloculata shows a nearly constant thickness and uniform Mg/Ca through the complete chamber wall. Patterns in thickness and Mg/Ca of the crust indicate that temperature is not the dominant factor controlling crust formation. Instead, we present a depth‐resolved model explaining compositional differences within individuals and between successive chambers as well as compositional heterogeneity of the crust and lamellar calcite in all three species studied here.