Collaborative Research: Volatile Sources and Sinks across the Mariana Forearc

合作研究：马里亚纳弧前的挥发性源和汇

• 批准号: 2152551
• 负责人: Peter Barry
• 金额: $ 31.18万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-09-01 至 2025-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2152551&HistoricalAwards=false
• 关键词: Collaborative; Research; Volatile; Sources; Sinks

Volatile elements such as helium (He), carbon (C), and nitrogen (N) are exchanged between Earth’s surface (atmosphere and oceans) and interior (crust and mantle) at volcanic arcs. When an oceanic tectonic plate sinks, or subducts, underneath a continental plate, forming a volcanic arc, these volatiles delivered by the oceanic plate are released in volcanos and seeps across the entire arc system. The efficiency of this transfer controls the composition of Earth’s mantle, atmospheric evolution, and possibly, the global distribution of microscopic life. Despite the importance of global-scale deep volatile cycles, volatile fluxes have not been extensively studied in submarine volcanic environments, as these regions are notoriously difficult to access. Subseafloor boreholes were recently installed in four active serpentinite mud volcanoes in the Southern Mariana forearc. These boreholes offer a unique opportunity to sample large volumes of deeply sourced volatile-laden fluids. This project will sample the boreholes for He, C, and N isotopes, as well as microbiology, to determine how deep volatile cycling is controlled by complex interactions between geochemical and biological processes in the Mariana forearc. These data will enable calculation of forearc volatile fluxes, quantifying biological and geochemical reactions by comparing fluxes of reactive volatiles (C, N) with inert indicators of mantle contributions (e.g., He) and the relative activity levels of known microbial metabolic pathways across the Mariana forearc. Results will be shared through peer-reviewed publications. In addition, a series of four classroom lectures aimed at a high-school level audience will be developed that leverages data and experiences from this project.Volatile elements are exchanged between Earth’s exterior (atmosphere and oceans) and interior (crust and mantle) at convergent margins. Volatiles are input via subduction and released in volcanos and seeps across the entire arc system. The efficiency of this transfer controls mantle heterogeneities, Earth’s redox conditions, atmospheric evolution, and possibly, the global distribution of microscopic life. Despite the importance of global-scale deep volatile cycles, volatile fluxes have not been extensively studied in submarine volcanic forearcs, as these regions are notoriously difficult to access. Recently emplaced boreholes provide a unique opportunity to sample large volumes of deeply-sourced pristine volatile-laden fluids across a wide expanse of the submarine Mariana forearc. However, volatile outfluxes may be complicated by the fact that shallow forearc temperatures are amenable to life, and thus some of these deeply derived (i.e., from the subducting slab and/or mantle) volatiles (e.g., CO2, CH4, NH4+) may be altered by subsurface microbes. This project will determine forearc volatile fluxes, quantifying biological and geochemical reactions by comparing fluxes of reactive volatiles (C, N) with inert indicators of mantle contributions (e.g., He) and the relative activity levels of known microbial metabolic pathways across a transect of the Mariana forearc. This project will leverage previously emplaced boreholes that have never been sampled for He, C, and N isotopes, or microbiology, to determine how volatile recycling efficiency is controlled by complex interactions between geochemical and biological processes in the Mariana forearc. Cased boreholes were recently installed in four active serpentinite mud volcanoes in the Southern Mariana forearc. Together, these four boreholes form a trench-parallel transect, enabling access to deep fluids from active serpentinite mud volcanoes across the Mariana forearc. This project will gather geochemical and biological data from these boreholes, enabling a systematic assessment of forearc volatile fluxes and the key processes (e.g., calcite precipitation, heterotrophy, autotrophy, respiration) mediating those fluxes. This will determine volatile (He, C and N) fluxes between Earth reservoirs and quantify their sources (slab, mantle wedge, crust) and sinks (geochemical and biological). Boreholes are located at different distances from the trench and the emanating fluids have varying pH and temperatures, so the dominant biological and geochemical processes at each borehole are expected to vary. In addition to training two PhD students and undergraduate students, the PIs have a broad outreach plan that incorporates media outlets and collaborations with science museums, underrepresented high schools, and undergraduate researchers. Specifically, the PIs will develop a series of four classroom lectures and activities aimed at a high-school level audience that leverages data and experiences from this project.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

氦（He）、碳（C）和氮（N）等挥发性元素在火山弧中在地球表面（大气和海洋）和内部（地壳和地幔）之间进行交换。当海洋构造板块下沉或俯冲到大陆板块之下，形成火山弧时，这些由海洋板块传递的挥发物在火山中释放，并渗透到整个弧系统中。这种转移的效率控制着地球地幔的组成、大气的演化，甚至可能控制着微观生命的全球分布。尽管全球规模的深层挥发性循环的重要性，挥发性通量还没有得到广泛的研究，在海底火山环境，因为这些地区是出了名的难以进入。最近在南马里亚纳前弧的四个活蛇纹岩泥火山中安装了海底钻孔。这些钻孔提供了一个独特的机会，采样大量的深源挥发性液体。该项目将对He，C和N同位素以及微生物学的钻孔进行采样，以确定马里亚纳前弧中地球化学和生物过程之间复杂的相互作用如何控制深层挥发性循环。这些数据将能够计算弧前挥发物通量，通过比较反应性挥发物（C，N）的通量与地幔贡献的惰性指标（例如，He）和马里亚纳前弧已知微生物代谢途径的相对活性水平。将通过同行评审的出版物分享成果。此外，还将利用该项目的数据和经验，为高中学生开设一系列四节课堂讲座：挥发性元素在地球外部（大气和海洋）和内部（地壳和地幔）会聚边缘之间进行交换。挥发物通过俯冲作用输入，在火山中释放，并渗透到整个弧系统。这种转移的效率控制地幔的不均匀性，地球的氧化还原条件，大气的演变，并可能，微观生命的全球分布。尽管全球规模的深层挥发性循环的重要性，挥发性通量没有得到广泛的研究，在海底火山前弧，因为这些地区是出了名的难以进入。最近安放的钻孔提供了一个独特的机会，在广阔的海底马里亚纳前弧的深源原始挥发性负载流体的大量样本。然而，由于浅弧前温度适合生命的事实，挥发性外流可能会变得复杂，因此这些深层来源的温度中的一些（即，来自俯冲板片和/或地幔）挥发物（例如，CO2、CH 4、NH 4+）可能被地下微生物改变。该项目将确定弧前挥发物通量，通过比较活性挥发物（C、N）通量和地幔贡献的惰性指标（例如，他）和已知的微生物代谢途径的相对活性水平在马里亚纳前弧的横断面。该项目将利用以前安置的钻孔从未进行过He，C和N同位素或微生物的采样，以确定挥发性回收效率如何受到马里亚纳前弧地球化学和生物过程之间复杂相互作用的控制。套管钻孔最近安装在四个活跃的蛇纹岩泥火山在南马里亚纳前弧。这四个钻孔一起形成了一个平行的沟样带，使人们能够从马里亚纳前弧的活蛇纹岩泥火山中获得深层流体。该项目将从这些钻孔中收集地球化学和生物数据，从而能够系统地评估弧前挥发性通量和关键过程（例如，方解石沉淀，异养，自养，呼吸）介导这些通量。这将确定地球水库之间的挥发性（He，C和N）通量，并量化其来源（板，地幔楔，地壳）和汇（地球化学和生物）。钻孔位于离海沟不同的距离处，流出的流体具有不同的pH值和温度，因此每个钻孔的主要生物和地球化学过程预计会有所不同。除了培训两名博士生和本科生外，PI还有一个广泛的推广计划，其中包括媒体渠道以及与科学博物馆、代表性不足的高中和本科研究人员的合作。具体来说，PI将开发一系列的四个课堂讲座和活动，针对高中水平的观众，利用数据和经验，从这个项目。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的知识价值和更广泛的影响审查标准的支持。