Collaborative Research: Volatile Sources and Sinks across the Mariana Forearc

诸如氦(He)、碳(C)和氮(N)等挥发性元素在火山弧处的地球表面(大气和海洋)和内部(地壳和地幔)之间进行交换。当大洋构造板块下沉或俯冲到大陆板块之下形成火山弧时，这些由大洋板块输送的挥发物在火山中释放，并渗透到整个弧系。这种转移的效率控制着地球地幔的组成、大气的演变，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循环很重要，但海底火山环境中的挥发通量还没有得到广泛的研究，因为这些地区是出了名的难以进入。最近在南马里亚纳弧前的四个活跃的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，可以对大量来源深厚的挥发性流体进行采样。该项目将对钻孔中的氦、碳和氮同位素以及微生物学进行采样，以确定马里亚纳弧前区复杂的地球化学和生物过程之间的复杂相互作用对挥发循环的控制程度。这些数据将能够计算弧前挥发通量，通过比较反应挥发分(C、N)的通量与地幔贡献的惰性指标(例如氦)和跨马里亚纳弧的已知微生物代谢途径的相对活动水平，量化生物和地球化学反应。结果将通过同行评议的出版物分享。此外，将利用该项目的数据和经验，开发一系列针对高中水平观众的四个课堂讲座。地球外部(大气和海洋)和内部(地壳和地幔)之间在汇聚边缘交换挥发性元素。挥发物通过俯冲输入，在火山中释放，并渗入整个弧系。这种转移的效率控制着地幔的不均一性、地球的氧化还原条件、大气演化，可能还控制着微观生命的全球分布。尽管全球规模的深层挥发循环很重要，但海底火山前弧中的挥发通量尚未得到广泛研究，因为这些地区是出了名的难以进入。最近部署的钻孔提供了一个独特的机会，可以在马里亚纳号海底弧前大片区域对大量来源深刻的原始挥发性流体进行采样。然而，由于浅层弧前温度适合生命这一事实，挥发性外流可能会变得复杂，因此其中一些深层次(即来自俯冲板和/或地幔)挥发分(例如，CO2、CH4、NH4)可能会被地下微生物改变。该项目将确定弧前挥发通量，通过将反应挥发分(C、N)通量与地幔贡献的惰性指标(例如氦)以及跨马里亚纳弧前横断面的已知微生物代谢途径的相对活动水平进行比较，量化生物和地球化学反应。该项目将利用以前部署的从未对He、C和N同位素或微生物进行采样的钻孔，来确定挥发性物质回收效率是如何由马里亚纳弧前的地球化学和生物过程之间的复杂相互作用控制的。最近在南马里亚纳弧前的四座活跃的蛇纹岩泥火山中安装了套管井。这四个钻孔一起形成了一个沟槽平行的横断面，使人们能够通过马里亚纳弧前活动的蛇纹岩泥火山获得深层流体。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性通量和调节这些通量的关键过程(例如方解石沉淀、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，并量化它们的源(板岩、地幔楔形、地壳)和汇(地球化学和生物)。钻孔位于与海沟不同的距离，释放的流体具有不同的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还有一个广泛的外展计划，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生研究人员的合作。具体地说，PIS将针对高中水平的受众开发一系列四个课堂讲座和活动，利用该项目的数据和经验。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.