Collaborative Research: Multiple Sulfur Isotope Tracers of the Subsurface Biosphere in Oceanic Basement

摘要：0622949/0622982/0623550 （Alt/Rouxel/Ono）知识优势：流体在低温（100℃）下通过洋中脊两侧的上层海洋地壳和海洋盆地进行循环，为地下生物圈提供了巨大的潜在栖息地。本工作验证了微生物硫酸盐还原发生在结晶性海洋基底岩（玄武岩和辉长岩）中的假设，这是影响海洋地壳硫平衡的一个广泛而重要的过程。研究计划包括确定蚀变洋底中硫(S)和硒（Se）的含量和稳定同位素比值。具体分析包括单个硫化物颗粒del 34S的离子探针分析，整个岩石S和Se含量，Se同位素和多硫同位素比值分析（del 33S， del 34S和del 36S）。这些数据有助于测试微生物特征，为流体演化提供证据，有助于限制氧化还原条件和岩石中S的来源（再活化的玄武岩硫化物或海水），并有助于了解微生物活动对海洋基底蚀变过程中S预算的影响。研究主要集中在已得到充分研究的ODP U1301地点的上层海洋基底，但也包括ODP 735B孔的辉长岩，以及对其他玄武岩基底的有限分析。研究结果有助于提高我们对海洋地壳蚀变过程中微生物活动的认识，并为建立地球化学与微生物学之间的联系提供依据。更广泛的影响：这项研究将分别支持华盛顿特区、马萨诸塞州和密歇根州的两名早期职业科学家和一名资深科学家。这项研究是由多机构参与的，并将吸引本科生参与研究。这项工作通过使用美国国家科学基金会海洋钻探项目收集的样本来利用美国国家科学基金会的投资。

ABSTRACT 0622949/0622982/0623550 (Alt/Rouxel/Ono)Intellectual Merit: Fluids circulate at low temperatures (100C) through the upper oceanic crust on mid ocean ridge flanks and in ocean basins providing vast potential habitats for a subsurface biosphere. This work tests the hypothesis that microbial sulfate reduction occurs in crystalline oceanic basement rocks (basalts and gabbros), and that it is a widespread and important processes affecting the sulfur budget of the oceanic crust. The research plan entails determining the contents and stable isotope ratios of sulfur (S) and selenium (Se) in altered oceanic basement. Specific analyses include ion microprobe analyses of del 34S of individual sulfide grains, whole rock S and Se contents, Se isotopes and multiple-sulfur isotope ratio analyses (del 33S, del 34S and del 36S). The data enable testing for microbial signatures, provide evidence for fluid evolution, help constrain redox conditions and the sources of S in the rocks (remobilized basaltic sulfide or seawater), and aid in understanding the effects of microbial activity on the budget for S during alteration of oceanic basement. The research focuses on upper oceanic basement from well-studied IODP Site U1301, but also includes gabbros from ODP Hole 735B, and limited analyses of other basaltic basement. Results of the work help improve our understanding of microbial activity during alteration of ocean crust, and provide a basis for establishing links between geochemistry and microbiology. Broader Impacts:This research will support two early career scientists and one senior scientist in Washington DC, Massachusetts, and Michigan, respectively. The research is multi-institutional and will engage undergraduates in research. The work leverages NSF investments by using samples collected by the NSF-Ocean Drilling program.