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

了解地球上的碳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要的科学目标，它对我们对生态系统和全球变暖的理解具有重要意义。海水通过深海热液喷口系统的循环导致了无机和有机碳化合物的广泛转化，并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道都集中在甲烷和轻烃上。然而，其他类型的有机化合物的分布和丰度仍然知之甚少。因此，深海热液系统对有机碳的贡献以及造成这种输入的生物地球化学过程仍然高度不确定。本研究对加勒比海开曼群岛中部的两个非常不同但位置相近的热液喷口排出的流体中碳化合物的组成和丰度进行了全面研究。这两个喷口位于完全不同的寄主岩石中，并且发生在非常不同的水深。它们的排气液温度也非常不同。流体将使用多个互补采样系统收集，并通过各种质谱和其他分析技术进行分析。通过比较这两个位置，可以确定在一系列物理和化学条件下的碳通量和化学转化。这项工作的更广泛的影响包括培训研究生和本科生最先进的地球化学方法，并为他们提供一个获得海上研究经验和培训的机会，这是一个强跨学科的学科。来自南卡罗来纳大学的一名研究生和几名本科生，南卡罗来纳大学是EPSCoR州（即，不接受大量联邦资金的州）；布里奇沃特州立大学（Bridgewater State University）为马萨诸塞州的经济弱势群体提供服务；和博尔德的科罗拉多大学将参与研究，并在科学巡航和支持实验室活动中发挥关键作用。在海洋地壳中，由于加热、矿物沉淀、岩浆注入和微生物活动等过程，存在于海上和海底以下的流体和固体中的碳化合物发生了广泛的转变。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道都集中在小的、挥发性的有机分子上，比如甲烷。然而，其他类型的有机化合物的丰度和命运仍然鲜为人知。为了更好地了解这些转变和海底热液系统中的碳量及其对深海微生物和生态的潜在影响，开曼群岛中部隆起（皮卡德和冯达姆）的两个组成和热不同的海底喷口系统发出的热液流体样本将在为期16天的海洋巡航中使用机器人车辆收集。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、生物质热蚀变、流体-岩石相互作用和微生物活动对脊顶热液中碳化合物储量的相对贡献；(2)寄主岩石、排气方式和温度如何影响轴向温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衍生的溶解有机碳的命运。(4)哪些有机化合物和特征是流体反应史的最佳地球化学指示物。将采用三种不同的采样设备，以确保捕获所有含碳化合物。将分析收集的样品的总体特征（溶解有机碳浓度和同位素）以及单个化合物的组成和同位素特征，范围从挥发性（例如甲烷和轻烃）到非挥发性（例如脂肪酸），从不稳定（例如氨基酸）到难降解（例如多环芳烃）。这些数据将允许计算每个地点的碳和同位素质量平衡。由此，将对两个系统中的碳的命运进行比较，以评估岩石类型、温度和排气方式对海底热液喷口中含碳化合物的重要性。额外的测量将进行非目标的广谱有机化合物分析，以确定变化趋势和碳化合物的演化。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。

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.