The oxygen isotope composition of diatom frustules, δ¹⁸O_diatom, is thought to reflect the isotopic composition of the ambient seawater at the time of biomineralization. However, the δ¹⁸O_diatom can be overprinted due to the susceptibility of silanol groups (both external and internal) to isotope exchange. Here, using high-resolution imaging, we investigate what factors may influence this post-mortem isotopic alteration during the initial stages of diagenesis in the sediment. A diatomaceous clay was incubated with ¹⁸O-enriched seawater with fresh diatom detritus placed at the sediment-water interface (SWI) and at depth in the sediment. NanoSIMS analysis showed that the fresh diatom detritus as well as fossil frustules became significantly enriched in ¹⁸O, and that a relationship between Al-content and ¹⁸O-exchange could be observed. To further study the potential role of Al as an inhibitor of oxygen exchange, we measured Al on the surface of fossil frustules and performed additional incubations of diatom detritus in seawater with various concentrations of dissolved Al. The presence of Al-rich material bound to the surface of fossil frustules did not reduce the extent of ¹⁸O-enrichment in the underlying silica. However, exposure of diatoms detritus to dissolved Al, which led to a significant increase in frustule Al/Si ratio and a homogenously distributed Al in the frustule valve, significantly lowered the amount of ¹⁸O-enrichment. We hypothesize that Al incorporated into the silica structure can slow down ¹⁸O exchange while Al present as surface contaminants (clays or other aluminosilicates) has no inhibitory role.

硅藻壳的氧同位素组成δ ¹⁸ O_硅藻被认为反映了生物矿化时周围海水的同位素组成。然而，由于硅醇基（外部和内部）对同位素交换的敏感性， δ ¹⁸ O_{硅藻可能被套印。}在这里，我们使用高分辨率成像研究了在沉积物成岩作用的初始阶段，哪些因素可能会影响这种死后同位素变化。将硅藻土与¹⁸在沉积物-水界面 (SWI) 和沉积物深处，含有新鲜硅藻碎屑的富氧海水。NanoSIMS分析表明，新鲜硅藻碎屑和硅藻壳化石明显富含¹⁸ O，并且可以观察到Al含量与¹⁸ O交换之间的关系。为了进一步研究 Al 作为氧交换抑制剂的潜在作用，我们测量了化石硅藻壳表面的 Al，并在具有不同浓度溶解 Al 的海水中对硅藻碎屑进行了额外的孵化。结合在化石硅藻壳表面的富铝材料的存在并没有减少¹⁸在下面的二氧化硅中富氧。然而，硅藻碎屑暴露于溶解的铝中，导致硅藻壳 Al/Si 比显着增加和硅藻壳阀中铝的均匀分布，显着降低了¹⁸ O-富集量。我们假设掺入二氧化硅结构中的 Al 可以减缓¹⁸ O 交换，而作为表面污染物（粘土或其他铝硅酸盐）存在的 Al 没有抑制作用。