Impact of biomineralization processes on the Mg content of foraminiferal shells: A biological perspective
Impact of biomineralization processes on the Mg content of foraminiferal shells: A biological perspective
复制标题
DOI：
10.1029/2005gc001015
复制
发表时间：
2006-01-26
影响因子：
3.5
通讯作者：
Erez, J
中科院分区：
文献类型：
--
作者：
Bentov, S;Erez, J
[1]有孔虫壳体中的Mg/Ca比值被广泛用作古温度的代用指标。尽管如此，有孔虫的基本镁含量似乎是由生物因素决定的，可以得出结论，从大的种间和壳内变异性和无机行为的频繁偏差。本文讨论了有孔虫控制或改变其壳中镁含量的三种可能途径：（1）有机基质参与沉淀过程，可能改变镁在生物方解石中的分配系数;（2）控制瞬时无定形相向方解石的转化;（3）改变晶体沉淀的母液中的镁浓度。前两种机制可能是负责沉淀的高镁方解石相（全壳或亚层），而第三种机制导致低镁方解石相的形成。我们提出了一种改编自上皮细胞的模型，可以从生物矿化位点大量去除Mg 2+。这种模式是特别相关的浮游和深底栖低镁有孔虫，经常用于古温度重建。我们讨论了可能的生物学作用的镁壳中的方解石多晶型物的保护，在体内的化学稳定性的壳，镁作为稳定剂的过渡阶段的功能和作为控制剂的沉淀过程。几个温度敏感的生物过程，可能会影响镁/钙比的壳的建议和模型，结合生物和无机的考虑。该模型使用镁的不均匀性，在壳与温度响应（生物和无机）的生物矿化过程中，占偏离浮游有孔虫无机方解石与海水平衡。
[1] The Mg/Ca ratio in foraminiferal shells is widely used as a proxy for paleotemperatures. Nevertheless, it seems that the basic Mg content of foraminifera is determined by biological factors, as can be concluded from the large inter species and intrashell variability and the frequent deviations from inorganic behavior. This paper discusses three possible ways by which foraminifera can control or modify the Mg content in their shell: ( 1) involvement of organic matrix in the precipitation process that may alter the partition coefficient of Mg in biogenic calcite, ( 2) controlled conversion of transient amorphous phases to calcite, and ( 3) modification of the Mg concentration in the parent solution from which the crystals precipitate. The first two mechanisms are probably responsible for the precipitation of high-Mg calcite phases ( whole shell or sublayers), while the third mechanism leads to the formation of low-Mg calcite phases. We propose a model adapted from epithelial cells that allows massive Mg2+ removal from the biomineralization site. This model is especially relevant to the planktonic and deep benthic low-Mg foraminifera that are frequently used for paleotemperature reconstructions. We discuss the possible biological roles of Mg in the shell in terms of the calcite polymorph conservation, the in vivo chemical stability of the shell, the functions of Mg as a stabilizer of transient phases and as a controlling agent of the precipitation process. Several temperature sensitive biological processes that may influence the Mg/Ca ratio of the shell are suggested and a model that combines biogenic and inorganic considerations is presented. The model uses Mg heterogeneity in the shell together with temperature response ( biologic and inorganic) of biomineralization processes, to account for the deviation of planktonic foraminifera from inorganic calcite at equilibrium with seawater.