Collaborative research: Investigating the Fate of Carbon at an Ultraslow Spreading Center

了解地球中碳的循环以及生物和非生物过程如何控制由此产生的含碳阶段的组成以及这些阶段如何随时间变化是一个重大的科学目标，对我们理解生态系统和全球变暖具有重要意义。 海水通过深海热液喷口系统的循环导致无机和有机碳化合物的广泛转化，可能对深海碳循环产生重大影响。迄今为止，关于深海热液中有机化合物的大多数报告集中在甲烷和轻烃。然而，其他类型有机化合物的分布和丰度仍然知之甚少。因此，热液系统对深海有机碳的贡献以及造成这一输入的地球化学过程仍然非常不确定。这项研究全面研究了加勒比海中开曼海脊超低速扩展的两个非常不同但位置接近的热液喷口排出的流体中碳化合物的组成和丰度。这两个喷口所在的寄主岩石大不相同，水深也大不相同。它们也具有非常不同的通风流体温度。 将使用多个互补采样系统收集液体，并通过各种质谱和其他分析技术进行分析。这两个网站之间的比较允许碳通量和化学转化，以确定在一系列的物理和化学条件。这项工作的更广泛影响包括培训研究生和本科生掌握最先进的地球化学方法，并为他们提供机会，在一个跨学科的课题中获得航海研究方面的经验和培训。来自EPSCoR州南卡罗来纳州大学的一名研究生和几名本科生（即，一个没有收到大量联邦资金的州）;布里奇沃特州立大学，为马萨诸塞州的经济弱势社区提供服务;和博尔德的科罗拉多大学将参与研究，并在科学考察和支持实验室活动方面发挥关键作用。在洋壳方面，由于诸如加热，矿物沉淀，岩浆的注入和微生物的活动。这些过程对当今和整个地质时期的全球元素循环产生了影响。迄今为止，大多数关于深海热液中有机化合物的报告都集中在甲烷等挥发性有机小分子上。然而，其他类型的有机化合物的丰度和命运仍然知之甚少。为了更好地了解这些变化和海底热液系统中的碳含量及其对深海微生物和生态的潜在影响，将利用机器人航行器进行为期16天的海洋学考察，收集开曼群岛中部海隆两个成分和热量不同的海底喷口系统（Piccard和von Damm）产生的热液样本。将使用质谱和其他分析工具分析样品的碳含量和碳化合物。该项目的目标是解决以下问题：（1）非生物合成、生物量热蚀变、流体-岩石相互作用和微生物活动对脊顶热液中碳化合物总量的相对贡献;（2）寄主岩石、喷发方式和温度如何影响轴向热泉中还原碳化合物的生成和稳定性;（3）海洋岩石圈循环过程中海水溶解有机碳的去向;（4）哪些有机化合物和特征是流体反应历史的最佳地球化学指标。将采用三种不同的采样装置，以确保捕获所有含碳化合物。将对采集的样品进行整体特性（溶解有机碳浓度和同位素）分析，并分析单个化合物的组成和同位素特性，从挥发性（如甲烷和轻质烃）到非挥发性（如脂肪酸），从不稳定性（如氨基酸）到难降解性（如多环芳烃）。这些数据将有助于计算每个地点的碳和同位素质量平衡。据此，将对两个系统中碳的去向进行比较，以评价岩石类型、温度和喷发方式对海底热液喷口中含碳化合物的重要性。通过非目标性的、广谱的有机化合物分析，将进行额外的测量，以确定蚀变趋势和碳化合物的演变。该奖项反映了NSF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。

Knowing the cycle of carbon in the Earth and how biological and abiological processes control the composition of the resulting carbon-bearing phases and how those change over time is a major scientific goal that has important implications for our understanding of both ecosystems and global warming. The circulation of seawater through deep-sea hydrothermal vent systems results in the extensive transformation of both inorganic and organic carbon compounds and may have a significant impact on the deep ocean carbon cycle. To date, most reports of organic compounds in deep-sea hydrothermal fluids have focused on methane and light hydrocarbons. The distribution and abundance of other types of organic compounds, however, remains poorly known. As a result, the contribution of hydrothermal systems to organic carbon in the deep ocean and the biogeochemical processes responsible for this input, remain highly uncertain. This research conducts a comprehensive study of the composition and abundance of carbon compounds from fluids discharging from two very different, but closely located, hydrothermal vents on the ultraslow spreading mid-Cayman rise in the Caribbean Sea. The two vent sites are located in substantially different host rocks and occur at very different water depths. They also have very different vent fluid temperatures. Fluids will be collected using multiple, complementary sampling systems and analyzed by various mass spectrometric and other analytical techniques. Comparison between these two sites allows carbon fluxes and chemical transformations to be determined over a range of physical and chemical conditions. Broader impacts of the work include training of graduate and undergraduate students in state-of-the-art geochemical methods and provide them with an opportunity to gain experience and training in sea-going research in a strongly interdisciplinary subject. A graduate and several undergraduate students from the University of South Carolina, an EPSCoR state (i.e., a state that does not receive significant federal dollars); Bridgewater State University, which serves economically disadvantaged communities in Massachusetts; and the University of Colorado at Boulder will be involved in the research and play key roles in both the scientific cruise and supporting laboratory activities.In ocean crust, extensive transformations occur to the carbon compounds present in both the fluids and solids on and below the seafloor due to processes such as heating, precipitation of minerals, injections of magma, and the activity of microorganisms. These processes have consequences for global elemental cycling in the present day and over geologic time. To date, most reports of organic compounds in deep-sea hydrothermal fluids have focused on small, volatile organic molecules such as methane. However, the abundance and fate of other types of organic compounds remains poorly known. To better understand these transformations and the amount of carbon in seafloor hydrothermal systems and their potential impact on deep sea microbes and ecology, samples of hydrothermal fluids emanating from two compositionally and thermally different seafloor vent systems on the mid-Cayman rise (Piccard and von Damm) will be collected on a 16-day oceanographic cruise using a robotic vehicle. Samples will be analyzed for their carbon content and carbon compounds using mass spectrometric and other analytical tools. Goals of the project are to addresses issues such as: (1) the relative contribution of abiotic synthesis, thermal alteration of biomass, fluid-rock interaction, and microbial activity to the inventory of carbon compounds in ridge-crest hydrothermal fluids, (2) how host rock, style of venting, and temperature influence the generation and stability of reduced carbon compounds in axial hot-springs, (3) the fate of seawater-derived dissolved organic carbon during circulation through the oceanic lithosphere, and (4) which organic compounds and signatures are the best geochemical indicators of fluid reaction history. Three different sampling devices will be employed to ensure the full range of carbon containing compounds is captured. Collected samples will be analyzed for bulk characteristics (dissolved organic carbon concentrations and isotopes) and for the composition and isotope characteristics of individual compounds, ranging from volatile (e.g. methane and light hydrocarbons) to non-volatile (e.g. fatty acids), and from labile (e.g. amino acids) to refractory (e.g. polycyclic aromatic hydrocarbons). These data will permit the calculation of carbon and isotope mass balances at each location. From this, a comparison of the fate of carbon in both systems will be carried out to evaluate the importance of rock type, temperature, and style of venting on the carbon-bearing compounds present in seafloor hydrothermal vents. Additional measurements will be made with non-targeted, broad spectrum organic compound analyses to identify alteration trends and carbon compound evolution.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.