Testing the Utility of Natural Variations in Isotopes of Si as a Proxy for Silica Production in the Sea

20世纪90年代中期，S发现硅藻在硅的生物成矿过程中分馏出硅的同位素，从而使人们有可能利用硅同位素在溶解硅和硅藻胞体中的自然变化作为一种工具来评估过去和现在的海洋中的二氧化硅产量。硅藻及其二氧化硅压舱物是有机物离开真光区的关键载体。它们对硅的专有需求意味着它们对初级生产力和生物碳泵的贡献可以由海洋表面水中硅酸的可用性来控制。硅藻和硅酸中硅同位素的自然变化为评估相对硅助剂在更长的时间尺度和更大的空间尺度上的使用提供了一种可能的手段，而不是目前可用的任何其他技术。尽管到目前为止的结果支持使用硅同位素的自然变化作为相对硅酸使用的替代物，但我们的知识中仍然存在两个关键空白。为了改进迄今进行的研究，来自加州大学圣巴巴拉分校的一名科学家将继续评估和校准d30Si替代物，方法是检查分馏因子(E)的变异性，以及水柱中的二氧化硅溶解和沉积物成岩过程中的二氧化硅溶解和交换过程是否影响硅藻小锥的d30Si特征。目前，尚不清楚e在海洋中是否存在区域差异，因为只有两个基于现场数据的e估计值可用。这给为培养的硅藻确定的分馏系数在全球海洋中的普遍适用性带来了极大的不确定性。此外，在二氧化硅溶解或交换和沉淀反应过程中的分馏可能会改变硅藻小锥的d30Si值，从而使仅根据假定的生物分馏进行的解释产生偏差。拟议研究的目标将是获得新的e的现场估计，并解决二氧化硅溶解和沉积物成岩作用期间的分馏问题，同时完善一种全新的方法，即通过酸解Cs2SiF6制备用于硅同位素分析的样品。。

ABSTRACTOCE - 0350576In the mid 1990's it was discovered that diatoms fractionate isotopes of silicon during silicon biomineralization opening the possibility of using natural variations in isotopes of silicon in dissolved Si and in diatom frustules as a tool for assessing silica production in both the past and present day ocean. Diatoms with their silica ballast are key vectors of organic matter out of the euphotic zone. Their obligate need for Si means that their contribution to primary productivity and the biological carbon pump can be controlled by the availability of silicic acid in ocean surface waters. Natural variations in isotopes of Si in diatoms and silicic acid offer a possible means of assessing relative silicic aid use on longer time scales and larger spatial scales than any other technique currently available. Though the results thus far support the use of natural variations in isotopes of Si as proxies for relative silicic acid use, two critical gaps in our knowledge remain.To improve the research performed to date, a scientist from the University of California- Santa Barbara will continue to evaluate and calibrate the d30Si proxy by examining the variability in the magnitude of the fractionation factor (e) as well as whether silica dissolution in the water column and silica dissolution and exchange processes during sediment diagenesis affect on the d30Si signature of diatom frustules. Currently, it is unclear whether e varies regionally in the sea as only two estimates of e based on field data are available. This imposes great uncertainty in the general applicability of the fractionation factor determined for cultured diatoms to the global ocean. Also, fractionation during silica dissolution or during exchange and precipitation reactions may alter d30Si values of diatom frustules biasing interpretations made solely on the basis of an assumed biological fractionation. The goal of the proposed research will be to obtain new field estimates of e and to address fractionation during silica dissolution and sediment diagenesis while also perfecting of an entirely new method of preparing samples for silicon isotope analysis through the acid decomposition of Cs2SiF6. .