Sedimentary specimens of the planktonic foraminifera Globorotalia inflata can provide information on subsurface conditions of past oceans. However, interpretation of their geochemical signal is complicated by possible effects of cryptic diversity and encrustation. Here we address these issues using plankton tow and sediment samples from the western South Atlantic, where two genotypes of G. inflata occur. To separate the genotypes, we analyzed shells from the extreme ends of the morphospace of G. inflata. The δ¹⁸O and δ¹³C of encrusted specimens from both morphotypes are indistinguishable. However, we do find a large influence of encrustation on δ¹⁸O and Mg/Ca. Whereas crust Mg/Ca ratios are at all locations lower than lamellar calcite, the crust effect on δ¹⁸O is less consistent in space. Plankton tows show that encrusted specimens occur at any depth and that even close to the surface crust Mg/Ca ratios are lower than in lamellar calcite. This is inconsistent with formation of the crust at lower temperature at greater depth. Instead we suggest that the difference between the crust and lamellar calcite Mg/Ca ratio is temperature‐independent and due to the presence of high Mg/Ca bands only in the lamellar calcite. The variable crust effect on δ¹⁸O is more difficult to explain, but the higher incidence of crust‐free specimens in warmer waters and the observation that a crust effect is clearest in the confluence zone, hint at the possibility that the difference reflects advective mixing of specimens from warmer and colder areas, rather than vertical migration.

中文翻译：

---

形态和结壳对Globorotalia inflata地球化学的影响

浮游有孔虫Globorotalia inflata的沉积标本可以提供有关过去海洋的地下状况的信息。然而，它们的地球化学信号的解释由于隐秘多样性和结壳的可能作用而变得复杂。在这里，我们使用来自南大西洋西部的浮游生物丝束和沉积物样本解决了这些问题，那里存在两种基因型的G. inflata。为了分离基因型，我们从G. inflata形态空间的末端分析了贝壳。的δ ¹⁸ O和δ ¹³从两个形态镶嵌试样C是不可区分的。然而，我们确实发现结壳δ上有很大的影响¹⁸O和Mg / Ca。而地壳的Mg / Ca比值是在所有地点比层状方解石降低，对δ地壳效果¹⁸ O为在空间不太一致。浮游生物丝束表明，在任何深度都存在结壳标本，甚至接近表壳的Mg / Ca比值也低于层状方解石。这与在较低温度，更大深度下地壳的形成不一致。相反，我们建议地壳和层状方解石的Mg / Ca比值之间的差异与温度无关，这是由于仅在层状方解石中存在高Mg / Ca谱带。上δ可变地壳效果¹⁸O很难解释，但是在较温暖的水中无壳样品的发生率较高，并且在汇合区结皮效果最明显的观察结果表明，这种差异可能反映了来自较热和较冷区域的样品的对流混合，而不是垂直迁移。