Silicon isotopes from IODP Site 323-U1340

The Bølling-Allerød deglacial event is marked by high diatom productivity and opal deposition throughout the subarctic Pacific. To investigate the cause of this event, we quantified several productivity-related sedimentary parameters that reflect the near-surface biogeochemistry from the Integrated Ocean Drilling Program (IODP) Site 323-U1340 in the Bering Sea. Silicon isotopes (δ29Si and δ30Si) from single-genus Coscinodiscus diatom frustules. Diatom silicon isotope values were generated in the Keck Laboratory at the University of California, Santa Cruz using the following methods. Freeze-dried samples were washed on a 63μm sieve to remove clays and dried in a 55°C oven. Samples were then cleaned with the M2 method, without the Calgon step, in non-glass containers and again oven-dried. To isolate a single diatom genus, samples were dry-sieved and ice rafted debris, radiolarians, spicules, and other genera were removed from the 63-125 μm portion by picking under a microscope and visually confirmed to be >99% Coscinodiscus specimens. Coscinodiscus species present were >95% Coscinodiscus marginatus with occasional Coscinodiscus oculus-iridis and Coscinodiscus radiatus. To dissolve samples, ≤0.002 g was transferred to 100 μL of 10 M NaOH in screw-top Teflon vials and reacted in Parr vessels at 200°C for three days. Samples were transferred to BioRad 50W X8 cation exchange columns previously cleaned with HCl and Milli-Q water (after Georg et al., 2006; doi:10.1016/j.chemgeo.2006.06.006), and eluted in Milli-Q water. Intensities of 28Si, 29Si and 30Si were measured using standard-sample bracketing on a Neptune MC ICP-MS at high resolution equipped with an Apex Omega desolvating nebulizer. All values are reported vs. NBS 28.

博令-阿勒罗德冰消期事件（Bølling-Allerød deglacial event）的典型特征为亚北极太平洋全域呈现高硅藻生产力与蛋白石沉积。为探究该事件的成因，我们对白令海综合大洋钻探计划（Integrated Ocean Drilling Program, IODP）323-U1340站位的沉积物中若干反映近表层生物地球化学过程的生产力相关沉积参数进行了定量分析，并测定了单属冠盘藻（Coscinodiscus）硅藻壳体的硅同位素（δ²⁹Si与δ³⁰Si）。硅藻硅同位素值的测定工作于加州大学圣克鲁兹分校凯克实验室（Keck Laboratory at the University of California, Santa Cruz）完成，具体实验流程如下：将冷冻干燥后的样品置于63μm筛网上冲洗以去除黏土，随后在55℃烘箱中烘干；随后采用不含六偏磷酸钠（Calgon）步骤的M2法对样品进行净化处理，全程于非玻璃容器中操作，完成后再次将样品置于烘箱中烘干。为分离得到单一硅藻属，先对样品进行干筛，随后在显微镜下挑除63~125μm粒径组分中的冰筏碎屑、放射虫、骨针及其他硅藻属物种，经目视确认冠盘藻（Coscinodiscus）占比≥99%；本次分离得到的冠盘藻物种中，95%以上为边缘冠盘藻（Coscinodiscus marginatus），偶见眼斑冠盘藻（Coscinodiscus oculus-iridis）和辐射冠盘藻（Coscinodiscus radiatus）。样品消解步骤为：称取≤0.002g样品置于螺口特氟龙（Teflon）瓶中，加入100μL 10M氢氧化钠（NaOH）溶液，随后将样品置于帕尔反应釜（Parr vessels）中于200℃下反应3天；将消解后的样品转移至经盐酸（HCl）与密理博超纯水（Milli-Q water）预处理的BioRad 50W X8阳离子交换柱中，使用密理博超纯水进行洗脱（实验方法参考Georg等人2006年的研究，doi:10.1016/j.chemgeo.2006.06.006）；采用标准样品间插法（standard-sample bracketing），在配备Apex Omega去溶剂化雾化器的高分辨率Neptune型多接收电感耦合等离子体质谱仪（MC ICP-MS）上测定28Si、29Si与30Si的信号强度。所有同位素值均以NBS 28为标准进行校正报告。