In search of the biosphere underneath the Lost City hydrothermal vent field using in-situ sulphur and multiple sulphur isotope signatures

该项目计划利用岩石学、原位硫和大块岩石的多重硫同位素特征作为工具，识别亚特兰蒂斯地块超基性岩石中的微生物活动，并进一步了解这一橄榄岩热液系统的热液历史。亚特兰提斯地块是一个由超基性和基性岩性组成的海洋核杂岩。它拥有失落之城热液区，从碳酸盐-水镁石烟囱中喷出高ph值，富含h2的低温流体。这些流体支持着碳酸盐烟囱内部和附近独特的微生物群落。然而，超镁铁质地下的生物活性程度并没有得到很好的限制。最近，IODP 357远征队前往亚特兰蒂斯地块，利用浅层钻井技术从失落之城热液区附近的浅层地下恢复了超镁铁性和基性岩性。这些样品提供了一个特殊的机会来研究发生在超镁质地下的过程。在拟议的研究中，大块岩石的多种硫同位素（32S, 33S, 34S, 36S）和单个硫化物颗粒的原位硫同位素特征将用于识别过去的微生物活动过程，如微生物硫酸盐还原，并测量与蛇纹石化相关的各种非生物成因过程。硫同位素数据将与拟议研究中进行的矿物学观察（例如硫化物矿物组合）以及从Exp. 357科学小组的其他成员那里收集的数据相结合，这些数据将提供对碳酸盐和蛇纹石脉中保存的流体化学的见解。这将更好地限制超基性岩石中微生物活动的程度，并可能为有利于地下生物圈微生物活动的条件提供新的见解。

The proposed project plans to use petrography, in-situ sulphur and bulk rock multiple sulphur isotope signatures as tools to identify microbial activity in ultramafic rocks of the Atlantis Massif and to give further insights into the hydrothermal history of this peridotite-hosted hydrothermal system. The Atlantis Massif is an oceanic core complex made up of ultramafic and mafic lithologies. It hosts the Lost City hydrothermal field, which vents high-pH, H2-rich, low-temperature fluids from carbonate-brucite chimneys. These fluids support a unique microbial community within and in the vicinity of the carbonate chimneys. However, the extent of biological activity within the ultramafic subsurface is not well constrained. The recent IODP Expedition 357 to the Atlantis Massif recovered ultramafic and mafic lithologies from the shallow subsurface of the vicinity of the Lost City hydrothermal field using shallow drilling techniques. These samples provide an exceptional opportunity to study the processes that take place within the ultramafic subsurface. In the proposed study bulk rock multiple sulphur isotopes (32S, 33S, 34S, 36S) and in-situ sulphur isotope signatures of individual sulphide grains will be used to identify processes of past microbial activity, such as microbial sulphate reduction, and to measure various abiogenic processes associated with serpentinization. The sulphur isotope data will be combined with mineralogical observations performed in the proposed study (e.g. sulphide mineral assemblages) as well as data collected from other members of the science party of Exp. 357 that provide insight into the fluid chemistry preserved within carbonate and serpentine veins. This will provide better constraints on the extent of microbial activity within the ultramafic rocks and may provide new insights into the conditions that favour microbial activity in the subsurface biosphere.