Resolving Past Changes in Ocean Oxygenation: Utility of Chromium Isotopes

解决过去海洋氧化的变化：铬同位素的用途

• 批准号: NE/H005749/1
• 负责人: Caroline Peacock
• 金额: $ 5.93万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FH005749%2F1
• 关键词: Resolving; Past; Changes; Ocean; Oxygenation

There is growing concern that a recent reduction in the concentration of dissolved oxygen in parts of the world's oceans signals a change in the Earth's climate. This is because there is lots of evidence in the geological record that links seawater oxygen to climate change- the anoxic (oxygen deficient) oceans at the end of the Permian (251 million years ago), for example, are associated with global warming and massive extinctions. Nevertheless, what we don't know, is exactly what controls the link between the concentration of dissolved oxygen and climate? Answering this question is extremely difficult because direct measurements of past levels of seawater oxygen, as well as climate parameters such as sea-surface temperature, extend back only as far as a few tens of years. Instead, we must rely on indirect, or so-called 'proxy' measurements that are preserved in the geological record. There are a number of 'proxies' for past levels of seawater oxygen. Most of them rely on measurements of the concentration of metals in marine sediments. However, it is now clear that metal concentrations can be affected by a number of different variables (for example, the level of primary productivity in the overlying water column), all of which can vary independently of seawater oxygen. One way to circumvent some of these problems is by analysis of the isotopes of these metals. In recent times, research has focused on the analysis of iron and molybdenum isotopes, but a key problem is that both iron and molybdenum are insensitive to small changes in seawater oxygen. They are only able to distinguish between oxic (oxygen-replete) or euxinic (no oxygen, high levels of hydrogen sulphide) conditions. For all of these reasons, there is a clear need to find new proxies for seawater oxygen. Chromium is an ideal candidate, for a number of reasons. Firstly, it is soluble under oxic conditions, but insoluble (and therefore accumulates in marine sediments) under slightly oxygen deficient conditions. Second, its isotopes behave very differently under oxic vs oxygen deficient conditions, and this can now be detected using state-of-the-art instrumentation. Third, the chemistry of chromium and its isotopes is relatively simple. The overarching aim of this project is to test the utility of chromium isotopes as a tracer of seawater oxygen. To this end, we will: (1) Measure the chromium isotope composition of marine sediments deposited in a range of oxygen conditions. (2) Determine the precise mechanism of chromium uptake into marine sediments, and the potential for movement of chromium after it has been buried. (3) Obtain records of chromium isotopes for a period of dramatic climate change. We expect the results of our research to provide an improved understanding of the relationships between seawater oxygen and global climate change. Such knowledge will be imperative for both the prediction and mitigation of Earth's climate in the future.

人们日益关切的是，最近世界部分海洋溶解氧浓度的减少表明地球气候发生了变化。这是因为地质记录中有大量证据将海水中的氧气与气候变化联系起来-例如，二叠纪末（2.51亿年前）的缺氧（缺氧）海洋与全球变暖和大规模干旱有关。然而，我们不知道的是，究竟是什么控制着溶解氧浓度和气候之间的联系？要弄清这个问题是极其困难的，因为直接测量过去的海水含氧量以及海洋表面温度等气候参数只能追溯到几十年前。相反，我们必须依靠间接的，或所谓的“代理”测量，这些测量保存在地质记录中。过去海水含氧量有许多“替代指标”。其中大多数依赖于对海洋沉积物中金属浓度的测量。然而，现在很清楚，金属浓度可能受到许多不同变量的影响（例如，上覆水柱中的初级生产力水平），所有这些变量都可以独立于海水氧气而变化。规避这些问题的一种方法是分析这些金属的同位素。近年来，研究主要集中在铁和钼同位素的分析上，但一个关键问题是铁和钼都对海水氧的微小变化不敏感。它们只能区分好氧（充满氧气）或缺氧（没有氧气，高水平的硫化氢）条件。由于所有这些原因，显然需要找到新的海水氧气替代物。铬是一个理想的候选人，原因有很多。首先，它在有氧条件下可溶，但在轻微缺氧条件下不溶（因此在海洋沉积物中积累）。其次，它的同位素在有氧和缺氧条件下的表现非常不同，现在可以使用最先进的仪器检测到。第三，铬及其同位素的化学性质相对简单。该项目的首要目标是测试铬同位素作为海水氧示踪剂的效用。为此，我们将：（1）测量在一定氧条件范围内沉积的海洋沉积物的铬同位素组成。(2)确定海洋沉积物吸收铬的精确机制，以及铬被掩埋后的移动潜力。(3)获取一段剧烈气候变化时期的铬同位素记录。我们希望我们的研究结果能够更好地了解海水氧气与全球气候变化之间的关系。这种知识对于预测和减缓未来地球气候都是必不可少的。

项目成果

Investigating Ocean Deoxygenation During the PETM Through the Cr Isotopic Signature of Foraminifera

• DOI: 10.1029/2018pa003372
• 发表时间: 2019-06
• 期刊: Paleoceanography and Paleoclimatology
• 影响因子: 3.5
• 作者: Serginio R. C. Remmelzwaal;Sophie Dixon;I. Parkinson;D. Schmidt;F. Monteiro;P. Sexton;M. Fehr;C. Peacock;Y. Donnadieu;R. James