Examining the role of biotic iron reduction as a life-sustaining process at the potential temperature limit of the deep subseafloor biosphere (IODP Expedition 370) (RESPIRE)

在海底深处生物圈的潜在温度极限下检查生物铁还原作为生命维持过程的作用（IODP Expedition 370）（RESPIRE）

• 批准号: 388260220
• 负责人: Dr. Susann Henkel
• 金额: --
• 依托单位: Alfred-Wegener-Institut (AWI) Helmholtz-Zentrum für Polar- und Meeresforschung
• 依托单位国家: 德国
• 项目类别: Infrastructure Priority Programmes
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/388260220?language=en
• 关键词: Examining; role; biotic; iron; reduction

This project will contribute to the research questions of IODP Expedition 370: T-Limit of the Deep Biosphere off Muroto. Temperatures at the Drill Site C0023 in the Nankai Trough (Japan) increase to ~120°C in 1.2 km depth and thus reach the maximum that can potentially be tolerated by microbes. However, a more reasonable T estimate for sterilisation of nutrient-poor deep sediments is 80-90°C. Aim of Expedition 370 was to assess how microbial communities change with depth, by which factors the changes are controlled and where microbial life ceases. It is part of the scientific program to investigate energy substrates available at depth and to identify unique geochemical and microbial signatures that differentiate the biotic and abiotic realms and/or their transitions. High-resolution and high-precision pore water data were produced enabling an identification of reaction fronts, potential microbial activity and hydrothermal alteration. A large part of the cored interval was methanic and sulfate-free. Microbial activity hence depends on electron acceptors other than sulfate. Recent studies indicate that the classical redox sequence needs to be complemented by Fe and Mn reduction in methanic sediments and that biogeochemical processes in natural systems show a stronger link to mineralogy than to a strict vertical sequence of reactions according to calculated energy yields. Fe(III) reduction is one of the most ancient forms of microbial respiration and iron reducers can grow under high T and pressure conditions, which suggests that Fe(III) reducers are potential candidates to survive close to T limit of the deep biosphere.We identified Fe and Mn reduction zones in methanic sediments of Site C0023. By applying sequential extractions we aim at assessing which Fe and Mn phases are available as electron acceptors and how strongly primary minerals have been diagenetically altered. Of particular interest are ash layers as those have been identified earlier as hotspots for microbial life. Ash layers are ubiqous in C0023 sediments and are typically rich in Fe and Mn.Microbial Fe reduction enriches 54Fe in pore water and, thus, authigenic Fe minerals (e.g. siderite, magnetite), whereas abiotic reactions with sulfide lead to more 56Fe in the dissolved phase. We aim at using stable Fe isotopes of dissolved and reactive solid Fe to discriminate microbial and abiotic drivers of Fe reduction. The d56Fe composition of solid Fe will be measured on Fe-carbonates, ferrihydrite + lepidocrocite, goethite + hematite and magnetite. The extent of sulfidation that has implications for the interpretation of magnetic property data will be determined by extracting acid volatile sulfur and chromium reducible sulfur. It is the aim of this project to assess the role of iron oxides for microbial respiration and the related diagenetic alterations in deep sediments of Site C0023.

该项目将为IODP 370考察队的研究问题做出贡献：Muroto外深层生物圈的温度极限。位于南开海槽(日本)的钻探现场C0023的温度在1.2公里深度内升至~120°C，从而达到微生物可能容忍的最高温度。然而，对于营养不良的深层沉积物的灭菌，更合理的T估计是80-90°C。考察370的目的是评估微生物群落如何随深度变化、由哪些因素控制变化以及微生物生命在哪里停止。这是科学计划的一部分，目的是调查深层可用的能量底物，并识别区分生物和非生物领域和/或它们的过渡的独特的地球化学和微生物特征。产生了高分辨率和高精度的孔隙水数据，从而能够识别反应前沿、潜在的微生物活动和热液蚀变。岩心段的大部分是甲烷和不含硫酸盐的。因此，微生物的活性依赖于硫酸盐以外的电子受体。最近的研究表明，甲烷沉积物中经典的氧化还原序列需要铁和锰的还原来补充，根据计算的能量产额，自然系统中的生物地球化学过程显示出与矿物学的更强的联系，而不是严格的垂直反应序列。Fe(III)还原是微生物呼吸作用最古老的形式之一，Fe(III)还原细菌可以在高温高压条件下生长，这表明Fe(III)还原细菌可能在接近深部生物圈T极限时存活。通过应用顺序提取法，我们的目的是评估哪些铁和锰相可用作电子受体，以及原生矿物的成岩作用有多强烈。尤其令人感兴趣的是火山灰层，因为这些层早些时候被确定为微生物生命的热点。C0023沉积物中普遍存在灰层，富Fe和Mn.微生物Fe还原使孔隙水中的54Fe富集成自生的铁矿物(如菱铁矿、磁铁矿)，而与硫化物的非生物反应导致溶解相中56Fe的增加.我们的目标是使用溶解的和活性的固体铁的稳定的铁同位素来区分铁还原的微生物和非生物驱动因素。固体铁的d56Fe组分将在碳酸盐铁、氢氧化铁+轻铁镁石、针铁矿+赤铁矿和磁铁矿上进行测定。对磁性数据解释有影响的硫化程度将通过提取酸挥发性硫和可还原铬硫来确定。本项目的目的是评估氧化铁对微生物呼吸的作用以及C0023站点深层沉积物中相关的成岩变化。