Collaborative Research: Volatile Sources and Sinks across the Mariana Forearc

挥发性元素，如氦（He）、碳(C)和氮(N)在地球表面（大气和海洋）和内部（地壳和地幔）的火山弧之间交换。当海洋构造板块下沉或俯冲到大陆板块下方，形成火山弧时，海洋板块带来的这些挥发物通过火山释放出来，渗透到整个火山弧系统中。这种转移的效率控制着地幔的组成、大气的演化，甚至可能控制着微观生命的全球分布。尽管全球尺度的深层挥发性旋回很重要，但在海底火山环境中尚未对挥发性通量进行广泛研究，因为这些区域众所周知难以进入。最近在南马里亚纳前弧的四个活跃的蛇纹岩泥火山上安装了海底钻孔。这些井眼提供了一个独特的机会，可以对大量深层含挥发物的流体进行取样。该项目将对钻孔进行He、C和N同位素以及微生物学采样，以确定在马里亚纳弧前，地球化学和生物过程之间的复杂相互作用如何控制深度挥发循环。这些数据将有助于计算弧前挥发物通量，通过将活性挥发物（C、N）的通量与地幔贡献的惰性指标（例如He）进行比较，以及整个马里亚纳弧前已知微生物代谢途径的相对活性水平，对生物和地球化学反应进行量化。研究结果将通过同行评审的出版物进行分享。此外，将利用这个项目的数据和经验，针对高中水平的听众开发一系列四次课堂讲座。挥发性元素在地球的外部（大气和海洋）和内部（地壳和地幔）之间交换。挥发物通过俯冲作用进入，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幔的非均质性、地球的氧化还原条件、大气演化，甚至可能控制着微观生命的全球分布。尽管全球尺度的深层挥发性旋回很重要，但由于海底火山前弧区域难以进入，因此尚未对这些区域的挥发性通量进行广泛研究。最近安置的井眼提供了一个独特的机会，可以在广阔的马里亚纳海底弧前取样大量深层原始挥发物。然而，由于弧前浅层温度适合生命存在，挥发性流出物可能会变得复杂，因此其中一些深层衍生（即来自俯冲板块和/或地幔）挥发物（如CO2、CH4、NH4+）可能会被地下微生物改变。该项目将确定弧前挥发物通量，通过将反应性挥发物（C、N）的通量与地幔贡献的惰性指标（例如He）进行比较，以及在马里亚纳弧前横断面上已知微生物代谢途径的相对活性水平，对生物和地球化学反应进行量化。该项目将利用以前从未采样过He、C和N同位素或微生物的钻孔，来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挥发性再循环效率。最近，在南马里亚纳（south Mariana）前弧的四座蛇纹岩泥火山上安装了套管井。这四个钻孔一起形成了一个与海沟平行的样带，使人们能够从活跃的蛇纹岩泥火山中获得穿过马里亚纳前弧的深层流体。该项目将从这些钻孔收集地球化学和生物数据，从而能够系统地评估弧前挥发通量和调节这些通量的关键过程（例如方解石降水、异养、自养、呼吸）。这将确定地球储集层之间的挥发性（He、C和N）通量，并量化它们的来源（板块、地幔楔块、地壳）和汇（地球化学和生物）。井眼距海沟的距离不同，且流出流体的pH值和温度也不同，因此每个井眼的主要生物和地球化学过程预计也会有所不同。除了培养两名博士生和本科生外，ppi还有一个广泛的推广计划，包括媒体和与科学博物馆、代表性不足的高中和本科生研究人员的合作。具体来说，pi将针对高中水平的受众开发一系列四次课堂讲座和活动，以利用该项目的数据和经验。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.