Magnesium, incorporated in foraminiferal calcite (Mg/CaCC), is used intensively to reconstruct past seawater temperatures but, in addition to temperature, the Mg/CaCC of foraminiferal tests also depends on the ratio of Mg and Ca in seawater (Mg/CaSW). The physiological mechanisms responsible for these proxy relationships are still unknown. This culture study investigates the impact of different seawater [Mg2 +] on calcification in two benthic foraminiferal species precipitating contrasting Mg/CaCC: Ammonia aomoriensis, producing low-Mg calcite and Amphistegina lessonii, producing intermediate-Mg calcite. Foraminiferal growth and test thickness were determined and, Mg/Ca was analyzed using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). Results show that at present-day seawater Mg/CaSW of ~ 5, both species have highest growth rates, reflecting their adaptation to modern seawater element concentrations. Test thickness is not significantly affected by different Mg/CaSW. The relationship between Mg/CaSW and Mg/CaCC shows a distinct positive y-axis intercept, possibly reflecting at least two processes involved in foraminiferal biomineralization. The associated Mg partition (DMg) changes non-linearly with increasing Mg/CaSW, hence suggesting that the DMg is best described by an exponential function approaching an asymptote.

中文翻译：

---

不同海水Mg2+浓度对两种底栖有孔虫钙化的影响

掺入有孔虫方解石 (Mg/CaCC) 中的镁被广泛用于重建过去的海水温度，但除了温度之外，有孔虫测试的 Mg/CaCC 还取决于海水中 Mg 和 Ca 的比例 (Mg/CaSW) . 负责这些代理关系的生理机制仍然未知。这项培养研究调查了不同海水 [Mg2 +] 对两种底栖有孔虫物种钙化的影响，两种底栖有孔虫物种沉淀出对比鲜明的 Mg/CaCC：青森氨水，生产低镁方解石和 Amphistegina courseii，生产中等镁方解石。测定了有孔虫的生长和测试厚度，并使用激光烧蚀-电感耦合等离子体质谱 (LA-ICP-MS) 分析了 Mg/Ca。结果表明，目前海水 Mg/CaSW 约为 5，这两个物种的增长率最高，反映了它们对现代海水元素浓度的适应。测试厚度不受不同 Mg/CaSW 的显着影响。Mg/CaSW 和 Mg/CaCC 之间的关系显示出明显的正 y 轴截距，可能反映了至少两个参与有孔虫生物矿化的过程。相关的 Mg 分配 (DMg) 随着 Mg/CaSW 的增加呈非线性变化，因此表明 DMg 最好用接近渐近线的指数函数来描述。