Collaborative Research: Hydrothermal Fluxes and their Impact on Ocean Biogeochemistry: An Integrated pre-and post-eruption Study at the EPR, 9-10 degrees N

知识价值：这项提议的目的是调查高温海底喷发的热液通量可能对上覆海洋的生物地球化学产生的影响。一个特别的焦点是铁的命运，与开阔的海洋水域相比，铁在喷口流体中得到了强烈的浓缩(约100万倍)。以往的研究估计，喷口释放的溶解铁在海底喷口附近被定量沉淀，并表明多金属硫化物和氢氧化铁颗粒的形成过程有可能显着改变热液流体的总通量。有人认为，在极限情况下，对热液颗粒的吸收甚至可能代表着一些溶解的化学收支的巨大沉没。为了研究这一点，我们提出了一项分析研究，收集在直接部署在北纬9 50‘N东太平洋隆起两个已知喷口地点附近的沉积物捕集器中的热液羽流颗粒。我们将分析该地点最近一次火山喷发(2005-06冬季)前后的样品。虽然已知这种喷发事件“可引发迅速演变的物理、化学和生物热液反应，但尚不清楚的是，这些瞬变效应对任何特定系统的时间平均热液通量可能有多大影响。通过将最近一次EPR 9-10 N喷发后几个月每周收集的样本与喷发前一年收集的样本进行比较，我们将独一无二地很好地回答这个问题。我们将调查沉积物圈闭中收集的多金属硫化物和氢氧化铁颗粒以及相关生物成因物质的矿物学和化学成分。我们将在我们的分析中使用元素和同位素技术，包括使用铁同位素潜在地指认“水热来源的铁和铀系列放射性核素作为从海水吸收的明确示踪剂。作为我们跨学科研究的一个组成部分，我们将通过对相同样本进行并行微生物调查来补充我们的地球化学工作。我们的微生物研究将特别集中在铁氧化细菌在控制深海热液来源铁的生物地球化学命运方面的作用。更广泛的影响：这项研究是一项多学科的机构间合作，支持三名教师、两名研究生和2-3名本科生的研究。我们的研究为另外两名职业生涯早期的博士后研究人员(一名女性)提供了更多的机会，他们正在开发与深海矿物相分析相关的最先进的分析技术。在对更广泛的科学界的影响方面，该项目将直接解决NSF Ridge 2000计划中的七个关键问题中的两个，这些问题涉及热液生物圈的界限和热液通量对海洋化学、物理和生物学的影响。目前通过我们的铁同位素研究验证的一个假说是，热液来源的铁不仅主导着深海中溶解的铁的收支，而且通过上升流，也作为一种重要的表层海洋生产力的微营养物质做出了重要贡献。因此，该项目有可能有助于在大洋中脊的固体-地球过程与对全球海洋碳循环和气候具有重要意义的过程之间建立直接联系。

Intellectual Merit: The objective of this proposal is to investigate the impact that hydrothermal fluxes from high-temperature seafloor venting may have on the biogeochemistry of the overlying ocean. One particular focus is the fate of iron, which is strongly enriched (ca. one million-fold) in vent-fluids when compared to open-ocean waters. Prior studies estimated that dissolved Fe released from venting is quantitatively precipitated close to seafloor vent-sites and demonstrated that the process of polymetallic sulfide and Fe-oxyhydroxide particle formation had the potential to significantly modify gross hydrothermal fluid fluxes. In the limit, it has been argued, uptake onto hydrothermal particles could even represent a significant sink for some dissolved chemical budgets. To investigate this, we have proposed an analytical study of settling hydrothermal plume particles collected in sediment-traps deployed directly adjacent to two known vent-sites on the East Pacific Rise at 9 50'N. The samples we will analyze date from both before and after a recent volcanic eruption at this site (Winter 2005-06). While it is known that such eruption events" can trigger rapidly evolving physical, chemical and biological hydrothermal responses, what remains unknown is how significant these transient effects might be to the time-averaged hydrothermal flux from any given system. By comparing samples collected at weekly intervals during the months immediately following the latest EPR 9-10 N eruptions with those collected during the year leading up to the eruption we will be uniquely well positioned to answer that question. We will investigate the mineralogy and chemical composition of polymetallic sulfide and Fe-oxyhydroxide particles collected within the sediment traps, as well as associated biogenic material. We will use elemental and isotopic techniques in our analyses including use of Fe isotopes to potentially fingerprint" hydrothermally-sourced Fe and U-series radionuclides as unambiguous tracers of uptake from seawater. As an integral part of our interdisciplinary study, we will complement our geochemical work with parallel microbial investigations of the same samples. Our microbial studies will, in particular, concentrate upon the role of Fe-oxidizing bacteria in controlling the biogeochemical fate of deep-ocean, hydrothermally-sourced iron. Broader Impacts: This research is a multi-disciplinary inter-institutional collaboration, which supports the research of three faculty, two graduate students, and 2-3 undergraduates. Our research offers additional opportunities in support of two other early-career postdoctoral researchers (one female) who are developing state-of-the-art analytical techniques pertinent to the analyses of deep-ocean mineral phases. In terms of impact on the broader science community, this project will directly address two of seven key questions from the NSF Ridge 2000 program concerning the limits of the hydrothermal biosphere and the impact of hydrothermal fluxes on ocean chemistry, physics and biology. One current hypothesis to be tested through our Fe-isotopic studies is that hydrothermally-sourced Fe not only dominates dissolved Fe budgets in the deep ocean but, through upwelling, also contributes significantly as an essential micro-nutrient for surface-ocean productivity. Thus, the potential exists that this project will help to establish a direct connection between solid-earth processes at Mid-Ocean Ridges and processes that are significant to global ocean carbon cycles and climate.