Organic Carbon in Altered Submarine Basalts: Tracing the Subsurface Biosphere and Role in the Global Carbon Cycle

最近的分析表明，海底玄武岩中有机碳的含量为百万分之几百。然而，这种碳在地下的分布和范围目前尚不清楚。由于海底玄武岩覆盖了地球表面的三分之二，其中所含的碳可能对全球碳循环很重要；这种碳及其特性有可能被用作地下生物圈的示踪剂。初步研究表明，海底玄武岩中硫和有机碳含量的升高以及同位素特征与表明这些岩石中存在硫酸盐还原微生物和产甲烷菌的功能基因以及基底流体中有机碳的变化相一致。虽然在许多不同的地下环境中已经测量了硫同位素，但在这些不同的环境中微生物对碳的影响尚不清楚。本研究将测量海底玄武岩中的碳含量和碳同位素特征，以追踪地下微生物作用的分布和程度。工作将包括分析大块岩石的总碳含量和有机碳含量，以及总碳和有机碳的13C/12C同位素比。这些数据将与研究者和他的合作者从相关研究中获得的硫同位素和微生物数据相结合，新的碳数据将更好地了解海洋基底的地下生物圈。样品将从三个代表不同热流体流动机制的深基底站点进行分析：(1)北大西洋，(2)西南太平洋和(3)东北太平洋。样品中的碳分布和生物效应将从矿物（厘米尺度）到岩石（几十到几百米）尺度进行检查。目的是了解这些元素和同位素指标与海洋地壳流体流动路径（蚀变晕、角砾岩）、岩性（块状玄武岩vs枕状玄武岩）和无机蚀变效应之间的关系。这将有助于更好地了解海底微生物活动的控制。不同岩石类型和流动状态的碳含量数据将用于计算当地和全球的质量平衡，目标是海底玄武岩中有机碳的作用和量化。这项工作的更广泛影响包括本科生的支持，并将其纳入整个科学过程。其他影响包括支持美国国家科学基金会资助的稳定同位素设施，将研究成果纳入大学水平的课程，以及与密歇根州安阿伯市的中学教师和学生进行推广和互动。

Recent analyses show that submarine basalts contain organic carbon at the level of a few hundred parts per million. The distribution and extent of this carbon in the subsurface, however, is presently not known. Because seafloor basalts cover two-thirds of Earth's surface, the carbon that is held within them may be important for the global carbon cycle; and it is possible that this carbon and its characteristics can be utilized as a tracer of the subsurface biosphere. Preliminary work shows that elevated sulfur and organic carbon contents and isotopic signatures in seafloor basalts are consistent with functional genes that indicate the presence of sulfate reducing microbes and methanogens in these rocks, as well as changes in the organic carbon in basement fluids. Although, sulfur isotopes have been measured in many different subsurface environments, the microbial impacts on carbon in these different settings is not known. This research will measure carbon contents and the isotopic signature of carbon in seafloor basalts to trace the distribution and extent of microbial effects in the subsurface. Work will include analyzing total carbon contents and the organic carbon content of bulk rocks and the 13C/12C isotopic ratios of both the total carbon and the organic carbon. These data will be combined with sulfur isotope and microbiological data from related studies by the investigator and his collaborators, with the the new carbon data providing a better understanding of the subsurface biosphere in oceanic basement. Samples will be analyzed from three deep basement sites that represent different thermal and fluid flow regimes: (1) the North Atlantic, (2) the southwest Pacific Ocean, and (3) the northeast Pacific Ocean. The distribution of carbon and biological effects in the samples will be examined from the mineral (centimeter scale) to the rock (tens to hundreds of meters) scale. Goals are to understand how these element and isotopic indicators are related to ocean crust fluid flow pathways (alteration halos, breccias), lithology (massive vs pillow basalt), and inorganic alteration effects. This will enable a better understanding of the controls on microbial activity in ocean basement. The data for carbon contents of different rock types and flow regimes will be used to calculate local and global mass balances, targeting the role and quantification of organic carbon in submarine basalts. Broader impacts of the work inclde undergraduate student support and incorportating them into the full scientific process. Additional impacts include support of an NSF-funded stable isotope facility, incorporation of reserch results into university level course work, and outreach and interactions with middle school teachers and students in Ann Arbor, Michigan.