Collaborative Research: IODP Expedition 329 Objective Research on Supply of H2 by Water Radiolysis in Subseafloor Sediment of the South Pacific Gyre

南太平洋环流（SPG）包含有在浅埋海洋沉积物中遇到的最低的细胞浓度和最低的微生物活动率。然而，维持其海底微生物生态系统的电子供体并没有完全受到限制。认识到这个天然实验室的重要性，综合大洋钻探计划（IODP）选择SPG作为其第一次专门研究海底生物的无立管探险的目标（远征329）。远征目标研究（EOR）提案有一个基本目标：为了量化SPG海底下沉积群落可能通过水辐解获得H2的程度，提出了以下可检验的假设：1）在SPG的贫有机质海底沉积物中，水辐解产生的H2相对于其他电子供体的速率显著。2）在海底以下一定深度，水辐解产生的H2速率超过了其他电子供体的可用性为检验这些假设，这项工作将侧重于四项相关活动：（1）放射性元素浓度和沉积物粒度的精确和准确定量，（2）从沉积物到间隙水的α粒子（4He）通量的定量，（3）通过代表性SPG沉积物样品的实验辐射来细化H2产率计算，以及（4）通过计算的H2产量与船上H2产量的直接比较来量化辐射分解H2对海底下沉积群落的潜在重要性这项研究将推进对地下世界的理解，（一）在何种程度上海底沉积生命可能是积极独立的表面光合世界和（ii）推进对地球沉积物中微生物能源来源的理解？最大的海洋省份。由于电子供体通量是如此之低，在SPG沉积物中，这项研究也可能有助于限制生命的限制。更广泛的影响，教育和数据管理这个项目将充分回答IODP远征329的主要目标之一，通过量化水辐解在SPG沉积物中产生的H2。它将解决另一个探险？的主要目标，通过推进对栖息地和代谢活动率在这个非常大的低能量环境的理解。该项目将加强URI（EPSCoR机构），BU和我们的Exp之间的合作。来自美国各地的329名合作者，欧洲、亚洲和澳大利亚。该项目将产生强大的培训影响。研究生将成为项目成员。本科生将包括作为论文答辩人，勤工俭学的学生，付费实验室助理，全国竞争NSF赞助的GSO夏季本科研究员，并通过我们的课程。URI地球生物学网站将扩大到包括对这个项目的关注。我们将通过客座讲座和互联网向观众展示我们的成果。从项目第二年开始，将提交重要的调查结果供出版。为了确保科学界和公众能够获得数据，将把数据存入SedDB数据库，并通过SESAR对样本进行编目。

Intellectual MeritThe South Pacific Gyre (SPG) contains the lowest cell concentrations and lowest rates of microbial activity ever encountered in shallowly-buried marine sediment. However, the electron donors that sustain its subseafloor microbial ecosystem are not fully constrained. In recognition of the importance of this natural laboratory, the Integrated Ocean Drilling Program (IODP) selected the SPG as the target of its first riser-less expedition solely dedicated to study of subseafloor life (Expedition 329).This Expedition Objective Research (EOR) proposal has one fundamental objective: To quantify the extent to which subseafloor sedimentary communities of the SPG may be supplied with H2 by water radiolysis.In addressing this objective, the following testable hypotheses are posed:1) H2 is produced by water radiolysis at significant rates relative to other electron donorsin the organic-poor subseafloor sediment of the SPG.2) At some depth below seafloor, the production rate of H2 by water radiolysis exceedsthe availability of other electron donors (organic matter and reduced minerals).To test these hypotheses, this work will focus on four related activities:(1) Precise and accurate quantification of radioactive element concentrations and sedimentary grain size,(2) Quantification of alpha particle (4He) fluxes from the sediment to the interstitial water,(3) Refinement of H2 yield calculations by experimental radiation of representative SPGsediment samples, and(4) Quantification of the potential importance of radiolytic H2 to the subseafloor sedimentary communities by direct comparison of calculated H2 yields to shipboard H2 concentration data and rates of organic matter oxidation derived from shipboard data.This study will advance understanding of the subsurface world by (i) placing a clear boundary on the extent to which subseafloor sedimentary life may be energetically independent of the surface photosynthetic world and (ii) advancing understanding of the sources of microbial energy in sediment of Earth?s largest oceanic province. Because electron donor fluxes are so low in SPG sediment, this research may also help to constrain the limits to life.Broader Impacts, Education, and Data ManagementThis project will fully answer one of the primary objectives of IODP Expedition 329 by quantifying the production of H2 by water radiolysis in SPG sediment. It will address another of the expedition?s primary objectives by advancing understanding of the habitats and rates of metabolic activities in this very large low-energy environment. The project will heighten collaborations between URI (an EPSCoR institution), BU, and our Exp. 329 collaborators from throughout the U.S., Europe, Asia and Australia. The project will have strong training impacts. Graduate students will be integral project members. Undergraduates will be included as thesis advisees, work-study students, paid laboratory assistants, nationally competed NSF-sponsored GSO Summer Undergraduate Research Fellows, and through our courses. The URI Geobiology website will expand to include focus on this project. We will present our results to audiences via guest lectures and the Internet. Significant findings will be submitted for publication beginning in the second year of the project. To ensure accessibility to the scientific community and the public, data will be deposited into the SedDB database and samples will be catalogued through SESAR.