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

智慧价值南太平洋环流(SPG)含有有史以来在浅埋海洋沉积物中遇到的最低细胞密度和最低微生物活动率。然而，维持其海底微生物生态系统的电子供体并未受到充分限制。考虑到这个天然实验室的重要性，综合海洋钻探计划(IODP)选择SPG作为其首次专门研究海底生命的无立管探险的目标(探险329)。这项探险目标研究(EOR)建议有一个基本目标：量化SPG的海底沉积群落通过水辐射分解提供氢的程度。为了解决这个目标，提出了以下可验证的假设：1)相对于其他电子供体，SPG的水以显著的速率辐射分解产生氢。2)在海底以下某个深度，SPG的贫有机海底沉积物中，水的辐解产生H2的速率超过了其他电子给体(有机质和还原矿物)的可获得性。为了验证这些假设，这项工作将集中在四个相关活动上：(1)精确和准确地量化放射性元素浓度和沉积粒度，(2)从沉积物到间隙水的α粒子(4He)通量的量化，(3)通过典型的SPG沉积物样品的实验辐射对H2产率计算的精确化，以及(4)通过将计算的氢产率与船上的氢气浓度数据和由船上的数据得出的有机质氧化速率的直接比较，量化辐射分解氢对海底沉积群落的潜在重要性。这项研究将通过(I)明确海底沉积生命可能在多大程度上独立于表层光合作用世界而加深对海底世界的理解，以及(Ii)增进对地球最大的海洋省--S--沉积物中微生物能量来源的理解。由于SPG沉积物中的电子给体通量如此之低，这项研究也可能有助于限制生命的极限。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产生的氢来完全满足IODP探险329的主要目标之一。它将通过促进对这个非常大的低能量环境中的栖息地和代谢活动速率的理解来解决另一个探险队的主要目标-S。该项目将加强URI(EPSCoR机构)、BU和我们Exp之间的合作。来自美国、欧洲、亚洲和澳大利亚的329名合作者。该项目将产生强大的培训影响。研究生将成为项目中不可或缺的成员。本科生将被包括为论文顾问、勤工俭学学生、受薪实验室助理、全国竞争的NSF赞助的GSO暑期本科生研究员，并通过我们的课程。URI地球生物学网站将扩大到包括对这一项目的关注。我们将通过客座讲座和互联网向观众展示我们的成果。重要的研究结果将于项目第二年开始提交供出版。为确保科学界和公众能够获得数据，数据将存入SedDB数据库，样品将通过SESAR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.