The oxygen isotopic composition (δ¹⁸O) of diatom frustules is potentially a quantitative paleoenvironmental proxy. However, δ¹⁸O analysis has some uncertainties because of difficulties in removing clay-mineral contamination and taxon-specific separation due to the small size of diatom frustules. The clay-mineral contamination seriously affects δ¹⁸O measurements, and the δ¹⁸O of bulk diatoms contains a mixture of information from diatoms living in various seasons and water depths. To resolve such problems, we established a new method for purifying the frustules of disc-shaped diatoms using a cell sorter and succeeded in removing the clay-mineral contamination and restricting the number of species for the δ¹⁸O analysis. We developed this method using samples from a sediment core retrieved from the Conrad Rise in the Indian Ocean sector of the Southern Ocean. First, the disc-shaped diatoms were enriched and cleaned by sieving, elutriation, and heavy-liquid separation. The samples were then further purified by a cell sorter. Regardless of the diatom assemblage or the sediment type in the core sample, this method generated samples consisting of more than 95% disc-shaped diatoms, dominated by Thalassiosira lentiginosa (Janisch) Fryxell, which occurs ubiquitously throughout the Southern Ocean. The δ¹⁸O profile for the sediment core obtained from purified disc-shaped diatoms showed the last glacial cycle since ca. 40 ka, which can be correlated with the LR04 benthic δ¹⁸O stack record and the temperature record in the EPICA Dome C ice core, indicating that this method can contribute to obtaining an accurate δ¹⁸O record of diatoms associated with glacial–interglacial cycles.

中文翻译：

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用细胞分选机从南大洋沉积物中纯化圆盘状硅藻以获得准确的氧同位素记录

硅藻壳的氧同位素组成 (δ ¹⁸ O) 可能是定量的古环境代理。然而，δ ¹⁸ O 分析具有一些不确定性，因为由于硅藻壳尺寸小，难以去除粘土矿物污染和分类群特异性分离。粘土矿物污染严重影响了 δ ¹⁸ O 测量，大块硅藻的 δ ¹⁸ O 包含来自生活在不同季节和水深的硅藻的混合信息。为了解决这些问题，我们建立了一种使用细胞分选机净化圆盘状硅藻壳的新方法，并成功地去除了粘土矿物污染并限制了δ ¹⁸的物种数量Ø 分析。我们使用从南大洋印度洋部分康拉德海隆提取的沉积岩芯样本开发了这种方法。首先，通过筛分、淘洗和重液分离对圆盘状硅藻进行富集和净化。然后通过细胞分选仪进一步纯化样品。无论岩心样品中的硅藻组合或沉积物类型如何，该方法生成的样品由超过 95% 的圆盘状硅藻组成，其中以Thalassiosira lentiginosa (Janisch) Fryxell 为主，它在整个南大洋中无处不在。从纯化的圆盘状硅藻中获得的沉积物核的 δ ¹⁸ O 剖面显示了自大约 20 年以来的最后一次冰川循环。40 ka，可与 LR04 底栖 δ ^{18 相关}O 堆栈记录和 EPICA Dome C 冰芯中的温度记录，表明该方法有助于获得与冰期-间冰期循环相关的硅藻的准确 δ ¹⁸ O 记录。