Collaborative Research: Hydrothermal vent systems mediate the formation and fate of refractory aromatic carbon in the deep ocean

海洋溶解有机碳(DOC)是地球上最大的还原碳库之一。这些DOC大部分被安置在深海中，在那里它的循环极其缓慢。放射性碳测年表明，海洋DOC中最古老的组分是稠合芳香族化合物。这些化合物也被认为是无活性和持久性的。该项目将通过在研究充分的东太平洋隆起9°N热液地点的实地活动，调查大洋中脊热液喷口是否是这部分深海DOC的来源。这项工作的结果将促进对深海及其沉积物中芳香碳库缓慢循环的理解，该碳库控制着碳在短时间和地质时间尺度上的固定。该项目涉及三名早期职业研究人员、一名博士后研究人员和两名研究生。最近在喷口流体中发现的(纳米)颗粒石墨，以及海洋底部水域中凝聚芳烃的类似海洋的同位素特征表明，这些凝聚芳烃有一个热液来源，值得进一步研究。这项拟议的研究建立在这项先前工作的基础上，提出了以下问题：热液喷口系统是否控制了深海中持续存在的难熔芳香碳的形成和分布？为了回答这个问题，将从研究充分的东太平洋隆起9°N段沿线的热液喷口区域收集样本，以针对三个主要目标：1)根据一系列集中和扩散的流体温度，量化和表征沿热液连续体的芳香碳和无机地球化学；2)确定热蚀变海洋有机质是否是热液喷口释放的耐火性芳香碳的主要来源；3)提供一个可以随未来工作验证和提炼的东太平洋深海颗粒和溶解难燃芳烃的热液通量、扩散和去向初步模型。使用多种分析替代物来量化和表征在广泛的地化范围内排放的石墨和煤烟型分子，将能够确定哪些水热条件有利于难熔芳香碳的生产。通过研究有机-无机相互作用，将产生新的数据集，用于阐明相互关联的生物地球化学过程。互补的同位素和分子测量将揭示热液芳香碳是否来自先前存在的海洋有机质的热蚀变，挑战了以前认为来自地幔的二氧化碳来源的假设。对离轴水和沉积物横断面的评估将确认存在于深海及其沉积物中的缩合芳香碳是否起源于热液。这一裁决反映了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。

Oceanic dissolved organic carbon (DOC) is one of the largest reservoirs of reduced carbon on Earth. Most of this DOC is housed in the deep ocean, where it cycles extremely slowly. Radiocarbon dating shows that the oldest components of oceanic DOC are condensed aromatic compounds. These compounds are also presumed to be unreactive and persistent. This project will investigate whether mid-ocean ridge hydrothermal vents are a source for this fraction of deep ocean DOC, through a field campaign at the well-studied East Pacific Rise 9°N hydrothermal site. Results of this work will advance the understanding of slowly cycling aromatic carbon pools in the abyssal ocean and its sediments, which controls the sequestration of carbon on short and geologic timescales. The project involves three early career researcher investigators, a postdoctoral investigator, and two graduate students.Recent discoveries of (nano)particulate graphite in venting fluids and marine-like isotopic signature of condensed aromatics in oceanic bottom waters suggests a hydrothermal source for those condensed aromatics and warrants further consideration. The proposed research builds upon this previous work by asking: Do hydrothermal vent systems control the formation and distribution of the refractory aromatic carbon that persists in the deep ocean? To answer this question, samples will be collected from hydrothermal vent fields along the well-studied East Pacific Rise 9°N segment to target three main objectives: 1) quantify and characterize aromatic carbon and inorganic geochemistry along a hydrothermal continuum from a range of focused and diffuse fluid temperatures, 2) determine whether thermally altered marine organic matter is the main source of refractory aromatic carbon emitted by hydrothermal vents, 3) provide a preliminary model of the hydrothermal fluxes, dispersal, and fate of particulate and dissolved refractory aromatic carbon in the deep Eastern Pacific Ocean that can be validated and refined with future work. Using multiple analytical proxies to quantify and characterize graphite and soot-type molecules emitted across a broad geochemical range of venting fluids will allow for the determination of which hydrothermal conditions are favorable for the production of refractory aromatic carbon. By studying organic-inorganic interactions, novel datasets for elucidating linked biogeochemical processes will be produced. Complementary isotopic and molecular measurements will reveal whether hydrothermal aromatic carbon is sourced from the thermal alteration of preexisting marine organic matter, challenging the previously-held assumption of a mantle-derived CO2 source. Assessment of off-axis water and sediment transects will confirm whether condensed aromatic carbon that persists in the deep ocean and its sediments is hydrothermal in origin.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.