Magnesium isotopic composition of tests of large benthic foraminifers: implications for biomineralization
Magnesium isotopic composition of tests of large benthic foraminifers: implications for biomineralization
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大型底栖有孔虫测试的镁同位素组成：对生物矿化的影响
DOI：
10.1029/2019gc008314
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
H.
中科院分区：
文献类型：
--
作者：
Maeda;A.;Yoshimura;T.;Araoka;D.;Suzuki;A.;Tamenori;Y.;Fujita;K.;Toyofuku;T.;Ohkouchi;N.;Kawahata;H.
生物源caco3中Mg同位素组成反映了海洋Mg循环，但由于海水温度和生物介导的同位素分馏的影响，其在古环境重建中的实际应用变得复杂。在本研究中，我们研究了形成大型底栖有孔虫测试的生物源高Mg方解石的水温、生长速率和Mg同位素比值（δ26Mg）之间的关系。我们在21-30℃下培养无性繁殖的大型底栖有孔虫（Amphisorus kudakajimensis和calcarina gaudichaudii）。我们测量了两种物种的Mg/Ca比、化学Mg形态和δ26Mg。两种植物的Mg/Ca比值均表现出明显的温度依赖性，而不同种群的δ26Mg值则不同。随着温度的升高，高笛沙二对重同位素的辨别能力增强。有孔虫近边结构光谱的X射线吸收表明，镁的形态与无机方解石的形态一致，表明在晶格中Mg取代了Ca的理想状态。这两个物种的δ26Mg值与无机方解石和其他沉积高Mg方解石的海洋生物的δ26Mg值接近。这些结果表明，两种物种的高Mg方解石试验的沉淀与无机方解石相似，两种物种的Mg同位素分馏只受与生长温度相关的个体生理过程的轻微影响。多个野外样品的δ 26Mgcarb‐solrange均落在无机方解石的∆26Mgcarb‐solrange范围内，这提供了初步证据，表明通过仔细选择样品进行分析，可以平均出δ26Mg值的种内差异的影响。
The Mg isotopic composition in biogenic CaCO3is expected to reflect oceanic Mg cycles, yet its practical application for paleoenvironmental reconstruction is complicated by the influences of seawater temperature and biologically mediated isotope fractionation. In this study, we investigated the relationship between water temperature, growth rate, and the Mg isotope ratio (δ26Mg) of the biogenic high‐Mg calcite that forms the tests of large benthic foraminifers. We cultured asexually reproduced large benthic foraminifers (Amphisorus kudakajimensisandCalcarina gaudichaudii) at 21–30 °C. We measured Mg/Ca ratios, chemical Mg speciation, and δ26Mg for both species. Mg/Ca ratios showed significant temperature dependence for both species, while the δ26Mg values for different populations ofC.gaudichaudiiexhibited increasing discrimination of heavy isotope with increasing temperature. X‐ray absorption of near‐edge structure spectra of the foraminiferal tests showed Mg speciation to be consistent with that of inorganic calcite, indicating ideal substitution of Mg for Ca in the crystal lattice. The δ26Mg values for both species were close to those of inorganic calcite and other marine organisms that precipitate high‐Mg calcite. These results suggest that precipitation of high‐Mg calcite tests for both species is similar to that of inorganic calcite and that Mg isotope fractionation for both species is only slightly influenced by individual physiological processes related to growth temperature. The ∆26Mgcarb‐solvalues of multiple field samples fell within the ∆26Mgcarb‐solrange for inorganic calcite, providing preliminary evidence that the effects of intraspecific differences in δ26Mg values can be averaged out by careful choice of samples for analysis.