Influence of hydroxamate siderophores on redox-sensitive trace elements and their isotopes and their relevance for the application of redox proxies in paleo-climate reconstruction studies

异羟肟酸铁载体对氧化还原敏感的微量元素及其同位素的影响及其与氧化还原代理在古气候重建研究中应用的相关性

• 批准号: 437594845
• 负责人: Professor Dr. Michael Bau, since 11/2021
• 金额: --
• 依托单位: Bundesanstalt für Geowissenschaften und Rohstoffe (BGR)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/437594845?language=en
• 关键词: Influence; hydroxamate; siderophores; redox; sensitive

In the natural environment, plants, microbes and fungi excrete a range of iron-specific organic chelators called siderophores. These molecules occur in almost all natural settings and are known to not only bind to Fe(III), but also have high complex stability constants with a range of other environmentally important trace metals, esp. to those that have a high charge and low ionic radius. These elements, i.e., Zr, Hf, the rare earth elements, Th, U and others, are referred to as high-field strength elements (HFSE) in geochemistry and are traditionally considered immobile during water-rock interaction unless a specific change in the oxidation state occurs, which may cause a different behavior of the redox-sensitive HFSE (i.e., U, Ce) and their isotopes in comparison to redox-insensitive HFSE. This observation is commonly used in paleoclimate studies to reconstruct past atmospheric oxygen levels. My pilot research indicates that the siderophore desferrioxamine B is able to bind to some of these redox-sensitive HFSE and enhances their mobility relative to the redox-insensitive HFSE during leaching from certain rock matrices. In the present proposal, I want to systematically investigate the potential impact of the DFOB siderophore on a range of redox-sensitive trace elements and their isotopes. In order to achieve this, I will conduct batch leaching experiments on natural rocks and I will also conduct scavenging experiments, both under oxic and anoxic conditions, in presence of siderophores as well as other organic ligands. The trace element and isotope studies will be complemented by XANES/EXAFS synchrotron radiation measurements to verify whether siderophores are actually able to oxidize redox-sensitive trace metals even under low oxygen conditions or whether other mechanisms cause the pronounced mobilization of redox-sensitive HFSE in presence of the DFOB siderophore. This study is filling an important research gap as the effects of extracellular biological compounds on these elements and isotopes in the natural environment are fairly unknown and it is also not clear whether the potential presence of such biogenic compounds may set limitations on the application of certain paleoredox proxies and whether intense biological activity during or after sediment deposition could lead to false-positives in paleoclimate reconstruction studies. The results of this project may also provide an idea on whether certain redox proxies, under certain circumstances, might indicate the presence of ‘life’ rather than the presence of oxygen, e.g., in the Meso- or Neoarchean. To achieve this goal, I will be collaborating with internationally renowned experts in the fields of trace element and isotope geochemistry and x-ray absorption spectroscopy.

在自然环境中，植物、微生物和真菌分泌一系列铁特异性有机螯合剂，称为铁载体。这些分子存在于几乎所有的自然环境中，并且已知不仅与Fe（III）结合，而且与一系列其他环境重要的痕量金属具有高络合稳定常数，特别是那些具有高电荷和低离子半径的金属。这些元素，即，Zr、Hf、稀土元素、Th、U等在地球化学中被称为高场强元素（HFSE），并且传统上被认为在水-岩石相互作用期间是不动的，除非发生氧化态的特定变化，这可能导致氧化还原敏感性HFSE的不同行为（即，U，Ce）及其同位素与氧化还原不敏感HFSE的比较。这种观测通常用于古气候研究，以重建过去的大气氧含量。我的试点研究表明，铁载体去铁胺B是能够绑定到这些氧化还原敏感HFSE和提高他们的流动性相对于氧化还原不敏感HFSE在某些岩石基质浸出。在本提案中，我想系统地研究DFOB铁载体对一系列氧化还原敏感的微量元素及其同位素的潜在影响。为了实现这一目标，我将进行天然岩石的批量浸出实验，我也将进行清除实验，无论是在有氧和缺氧条件下，在铁载体以及其他有机配体的存在下。微量元素和同位素的研究将补充XANES/EXAFS同步辐射测量，以验证铁载体是否实际上能够氧化氧化还原敏感的微量金属，即使在低氧条件下，或是否其他机制导致氧化还原敏感的HFSE在DFOB铁载体的存在下明显的动员。这项研究填补了一个重要的研究空白，因为细胞外生物化合物对自然环境中这些元素和同位素的影响是相当未知的，也不清楚这种生物源化合物的潜在存在是否会限制某些古氧化还原代理的应用，以及沉积物沉积期间或之后的强烈生物活动是否会导致古气候重建研究的假阳性。这个项目的结果也可能提供一个想法，在某些情况下，某些氧化还原代理是否可能表明存在“生命”，而不是氧气的存在，例如，在中太古代或新太古代。为了实现这一目标，我将与微量元素和同位素地球化学以及X射线吸收光谱学领域的国际知名专家合作。