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

摘要0622949/0622982/0623550(Alt/Rouxel/Ono)学术价值：流体在低温(100摄氏度)下通过大洋中脊侧翼的上层洋壳和洋盆循环，为地下生物圈提供了巨大的潜在栖息地。这项工作验证了微生物硫酸盐还原发生在结晶性大洋基岩(玄武岩和辉长岩)中的假设，以及这是一个广泛而重要的影响洋壳硫收支的过程。研究计划包括测定蚀变洋底中硫(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的Del 34S离子探针分析、全岩S和Se含量分析、Se同位素和多硫同位素比值分析(Del 33S、Del 34S和Del 36S)。这些数据使微生物特征测试成为可能，为流体演化提供证据，有助于限制氧化还原条件和岩石(可再活化的玄武岩硫化物或海水)中S的来源，并有助于理解微生物活动对大洋基底改造期间S预算的影响。研究主要集中在IODP站位U1301的大洋上部基底，但也包括735B孔的辉长岩，以及对其他玄武岩基底的有限分析。这项工作的结果有助于加深我们对海洋结壳变化过程中微生物活动的理解，并为建立地球化学与微生物学之间的联系提供了基础。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。这项研究是多机构的，将吸引本科生参与研究。这项工作通过使用NSF海洋钻探计划收集的样本来利用NSF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.