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）的细胞浓度和微生物活动率在浅埋海洋沉积物中是最低的。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，综合海洋钻井计划（IODP）选择SPG作为其第一个专门研究海底生物的无隔水管探险（远征329）的目标。这项远征目标研究（EOR）提案有一个基本目标：量化SPG海底沉积群落可能通过水辐射分解提供氢气的程度。为了实现这一目标，提出了以下可测试的假设：1)相对于其他电子供体，在spg海底沉积物中，水辐射分解产生H2的速率显著高于其他电子供体（有机物和还原矿物）。2)在海底以下的某些深度，水辐射分解产生H2的速率超过了其他电子供体（有机物和还原矿物）的可用性。为了验证这些假设，本工作将集中在四个相关活动上：(1)精确和准确地定量放射性元素浓度和沉积粒度；(2)定量从沉积物到间隙水的α粒子（4He）通量；(3)通过代表性spg沉积物样品的实验辐射改进H2产率计算。(4)通过将计算出的H2产率与船载H2浓度数据和由船载数据得出的有机质氧化速率直接比较，量化辐射分解H2对海底沉积群落的潜在重要性。这项研究将通过以下方式促进对地下世界的理解：(1)明确海底沉积生命在多大程度上可以在能量上独立于地表光合作用世界；(2)促进对地球沉积物中微生物能量来源的理解。中国最大的海洋省份。由于SPG沉积物中的电子供体通量非常低，因此这项研究也可能有助于限制生命的极限。更广泛的影响，教育和数据管理该项目将通过量化SPG沉积物中水辐射分解H2的产量，完全满足IODP 329考察的主要目标之一。它会提到另一个探险队？在这个非常大的低能量环境中，通过提高对栖息地和代谢活动速率的理解，是美国的主要目标。该项目将加强URI （EPSCoR机构），BU和来自美国，欧洲，亚洲和澳大利亚的Exp. 329合作者之间的合作。该项目将对培训产生重大影响。研究生将是项目不可或缺的成员。本科生将被包括为论文导师、勤工俭学学生、带薪实验室助理、全国竞争的nsf赞助的GSO夏季本科生研究研究员，以及通过我们的课程。URI地理生物学网站将扩展以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研究结果。重要的发现将在项目的第二年开始提交出版。为了确保科学界和公众能够获取，数据将被存入sedb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.