Collaborative Research: A multidimensional approach to understanding microbial carbon cycling beneath the seafloor during cool hydrothermal circulation

全球海洋包含着地球上最大的微生物群，至少有一半的海洋微生物生物量出现在海底之下。特别是，海洋地壳包含着地球上最大的含水层，其液体体积约等于海洋体积的2%。它还拥有大量微生物生命，可能影响全球尺度的生物地球化学循环。这个项目调查了地球上最大的活跃流动的含水层系统——在海洋和沉积物下面的海洋地壳中循环的流体。尽管人们对深海生命的认识不断进步，但对岩石海洋地壳中的微生物和流经它的流体的了解仍然很初级。这个项目的重点是了解凉爽的海底生物圈中微生物活动与碳循环之间的联系。地壳生物圈内有机碳消耗和有机碳产生代谢之间的平衡将由国际海洋发现计划（IODP）在大西洋中脊侧翼建立的海底观测站来确定，这可能代表了全球大部分热液流体循环。微生物转化碳的速率将采用地球化学和生物学两种方法来确定。研究结果将有助于确定海底微生物介导的过程对海洋碳循环的影响程度。这项工作将首次全面描述寒冷的含氧地壳含水层中的碳循环。两名女博士后将获得资助，高中和社区大学的学生也将通过与科德角社区学院、剑桥-林奇和拉丁学校的合作参与其中。其目标是通过实践研究经验、对等指导和专业发展机会，在高中和社区大学学生中提高科学、技术、工程和数学素养。该项目的目标是回答“冷地壳海底生物圈是净自养的还是净异养的？”这项工作的重点是在北池，这是一个孤立的沉积物池，位于大西洋中脊西侧的海洋地壳侧面，距今700万至800万年。该项目的两个目标是：1。表征海底流体中悬浮颗粒的无机和有机碳含量，以及天然14C和13C同位素比率，以确定微生物介导的通量和过程。描述颗粒相关和自由生活的微生物群落对海底流体初级生产和再矿化的净影响，以及对这些相同过程的分类群特异性贡献。同位素地球化学和分子生物学方法的结合，代表了对年轻海洋地壳海底生物圈微生物生态学和地球化学及其在维持全球深海氧化还原平衡中的作用的理解取得了重大的跨学科进展。预期结果包括确定颗粒相关和自由生活的海底微生物群落自养和异养代谢的特征，以及自养和异养代谢和相关分类丰度的量化，以提供对地壳流体中碳通量的净和特定微生物过程的见解。

The global ocean comprises Earth's largest microbiome, with at least half of the ocean's microbial biomass occurring beneath the ocean floor. In particular, oceanic crust encompasses the largest aquifer on Earth, with a liquid volume equal to approximately 2% of the ocean's volume. It also harbors a substantial reservoir of microbial life that may influence global-scale biogeochemical cycles. This project investigates this largest actively flowing aquifer system on Earth- the fluids circulating through oceanic crust underlying the oceans and sediments. Despite advancing knowledge about life in the deep ocean, the understanding of microorganisms in the rocky oceanic crust and the fluids flowing through it remains rudimentary. This project is focused on understanding the linkages between microbial activity and the cycling of carbon in the cool, subseafloor biosphere. The balance between organic carbon-consuming and organic carbon-producing metabolisms within the crustal biosphere will be determined using seafloor observatories put in place by the International Ocean Discovery Program (IODP) on the flanks of the Mid-Atlantic Ridge, likely representative of the majority of global hydrothermal fluid circulation. The rates of microbial transformations of carbon will be determined using both geochemical and biological approaches. Results will help establish the extent to which microbially-mediated processes in the subseafloor influence carbon cycling in the ocean. This work will represent the first comprehensive description of carbon cycling in the cold oxic crustal aquifer. Two female postdocs will be supported on the grant, and both high school and community college students will also be involved through collaborations with Cape Cod Community College and Cambridge-Rindge and Latin School. The goal is to promote science, technology, engineering and math literacy among high-school and community college students through hand-on research experiences, peer-to-peer mentoring, and professional development opportunities. The goal of the project is to answer the question "is the cool crustal subseafloor biosphere net autotrophic or net heterotrophic?" The focus of the effort is at North Pond, an isolated sediment pond located on ridge flank oceanic crust 7-8 million years old on the western side of the Mid-Atlantic Ridge. The two objectives of the project are to:1. Characterize suspended particles in subseafloor fluids with respect to their inorganic and organic carbon content, and natural 14C and 13C isotopic ratios, to determine microbially-mediated fluxes and processes.2. Characterize the net influence of particle-associated and free-living microbial communities on subseafloor fluid primary production and remineralization, as well as the taxon-specific contributions to these same processes.The integration of isotope geochemical and molecular biological approaches represents a significant cross-disciplinary advance in the understanding of the microbial ecology and geochemistry of the subseafloor biosphere in young oceanic crust and their role in maintaining global deep-sea redox balance. Expected outcomes include identifying signatures of autotrophic and heterotrophic metabolism in particle-associated and free-living subseafloor microbial communities as well as quantification of autotrophic and heterotrophic metabolism and associated taxon-abundances to provide insights into the net and specific microbial processes in crustal fluids on carbon fluxes.