Molybdenum Isotopes in the Geologic Record: Paleoredox Proxies?

地质记录中的钼同位素：古氧化还原代用物？该项目旨在研究元素钼（Mo）同位素组成的自然变化。钼是一种对氧敏感的元素。随着环境中氧含量的变化，mo的化学行为也会发生变化。我们进行了初步研究，发现富氧条件下海水中积累的Mo比无氧条件下有硫的沉积物中积累的Mo要轻。在这两种类型的积累中，Mo在无氧条件下的积累与海水中的Mo相似。因此，我们认为富氧条件下从海洋中提取的轻Mo相对比例的变化将反映在海水和无氧条件下沉积的沉积物中的Mo同位素组成中。富含氧气的海洋越多，从海水中提取的轻Mo就越多，海水中剩余的Mo就会变得更重。这一假设的关键是在富氧条件下从海水中提取轻Mo。因此，本项目的目的是在实验室和天然样品中调查这一过程，以了解所涉及的机制并量化其影响。如果我们是正确的，那么在无氧水域沉积的沉积物中Mo的同位素组成可以用来追踪富氧和无氧海水随时间的相对比例。了解我们今天富氧海洋的进化是了解地球环境和生命本身从原始时代到现在进化的关键之一。

ABSTRACTMolybdenum Isotope in the Geologic Record: Paleoredox Proxies?This project aims to investigate natural variations in the isotopic composition of the element molybdenum (Mo). Mo is an element that is sensitive to the presence of oxygen.As the abundance of oxygen in the environment varies, so does the chemical behavior ofMo. We have made a preliminary study and found that Mo that has accumulated from seawater under oxygen-rich conditions is lighter than Mo that accumulates in sediments under oxygen-absent conditions in the presence of sulfur. Of the two types of accumulation, it is the Mo that accumulates under oxygen-absent conditions that is similar to Mo in seawater. We therefore believe that changes in the relative proportion of light Mo extracted from the oceans under oxygen-rich conditions will be reflected in the isotopic composition of Mo in seawater and in sediments deposited under oxygen-absent conditions. The more of the ocean that is oxygen-rich, the more light Mo will be extracted from seawater and the heavier the Mo remaining in seawater will become.The key to this hypothesis is the extraction of light Mo from seawater under oxygen-rich conditions. It is therefore the purpose of this project to investigate this process both in the laboratory and in natural samples in order to understand the mechanisms involved and to quantify their effects.If we are correct, then the isotopic composition of Mo in sediments deposited under oxygen-absent waters could be used to track the relative proportions of oxygen-rich and oxygen-absent ocean water through time. An understanding of the evolution of our present-day oxygen-rich ocean is one of the keys to understanding the evolution of theEarth 's environment, and of life itself, from primordial times to the present.