Collaborative Research: Elucidating Brine-Dominated, Segment-Scale Hydrothermal Discharge Along The Cleft Segment, Juan de Fuca Ridge

胡安德富卡海脊上的热液卤水新的洋壳是由注入海底的岩浆形成的，然后被海水循环冷却。这种热液循环在热岩和海水之间交换热量和化学物质，从而产生矿藏和独特的海底生态系统。岩浆的注入是不规则的，海底热液循环和排出流体的组成也是如此。在岩浆注入事件期间和之后，加热的海水分离成缺乏许多溶解金属的低盐度蒸气相和高盐度富含金属的盐水相。海底蒸汽排放通常是短暂的（数年），随后是一个更长的阶段（几十年至几百年或更长）的盐水排放。目前对卤水成分及其时空演变的了解有限。在这次调查中，将对俄勒冈州海岸外胡安德富卡海岭裂缝段的热液流体沿着进行取样，并分析其化学成分。这部分年轻的洋壳在1986年经历了一次岩浆活动，三十多年来一直在排放盐水。这些流体组成的系统性变化将使我们能够记录以盐水为主的海底热液系统的长期演变（几十年），表征盐水相中溶解的矿物和气体的运输，并有助于我们理解地壳和海洋之间的元素交换。岩浆侵入洋壳，在海洋岩石圈内的对流循环过程中导致海水的热和化学改性，然后排放到海底。这种热液排放影响海洋的生物地球化学循环、海底富金属矿床的形成和海底生态系统。热液活动的周期性时空演变决定了净效应。许多系统开始以短寿命（数年）的蒸气相的排放开始，并发展为长寿命（数十年至数百年甚至更长）的盐水相的排放。相对于以蒸汽为主的热液体系，以卤水为主的热液体系的系统时间序列研究还很有限。了解以盐水为主的热液系统特别重要，因为岩浆驱动的海底下热液循环的数值和概念模型表明，以盐水为主的流体的这种循环可以持续数百年或更长时间，并可能影响从岩石圈到海洋的全球元素通量。气密性流体取样器将收集裂缝段的热液排放，裂缝段至少32年来一直从同一海底特征排放以盐水为主的热液流体。此外，研究人员将测量排出温度，部署和恢复短期连续液体采样器，并部署遗留研究的温度记录仪。基于海岸的流体表征计划的结果将解决长期稳定性，连通性和潜在的变化，在地下，段规模的过程中，在盐水为主的热液系统。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Hydrothermal Brines on the Juan de Fuca RidgeNew oceanic crust is formed by magma that is injected beneath the seafloor and then cooled by seawater circulation. This hydrothermal circulation exchanges heat and chemicals between hot rocks and seawater, which produces mineral deposits and unique seafloor ecosystems. The injection of magma is irregular as is subseafloor hydrothermal circulation and the composition of the discharging fluid. During and after a magmatic injection event, the heated seawater separates into a low salinity vapor phase lacking many dissolved metals and a high salinity metal-rich brine phase. Seafloor discharge of the vapor is typically short-lived (years) and is followed by a much longer phase (decades to centuries or longer) of brine discharge. Knowledge of brine composition and its temporal and spatial evolution is currently limited. During this investigation hydrothermal fluids along the Cleft Segment of the Juan de Fuca Ridge off the coast of Oregon will be sampled and analyzed for their chemical composition. This portion of young oceanic crust experienced a magmatic event in 1986 and has been discharging brines for more than three decades. Systematic variations in the composition of these fluids will allow us to document the long-term evolution (decades) of brine-dominated submarine hydrothermal systems, characterize the transport of dissolved minerals and gases in brine phases, and contribute to our understanding of element exchange between Earth’s crust and ocean. The intrusion of magma into the oceanic crust results in the thermal and chemical modification of seawater during convective circulation within the oceanic lithosphere before discharging at the seafloor. This hydrothermal discharge impacts biogeochemical cycles in the ocean, the formation of seafloor metal-rich mineral deposits, and seafloor ecosystems. The net effect is dictated by cyclic temporal and spatial evolution of hydrothermal activity. Many systems begin with discharge of a short-lived (years), vapor phase and evolve to a longer-lived (decades to centuries to longer) discharge of brine phase. Relative to vapor-dominated hydrothermal systems, systematic time-series studies of brine-dominated systems are limited. Understanding brine-dominated hydrothermal systems is particularly important because numerical and conceptual models of magma-driven subseafloor hydrothermal circulation indicate that such circulation of brine-dominated fluids can last for centuries or longer, and potentially impact global fluxes of elements from the lithosphere to the ocean. Gas-tight fluid samplers will collect hydrothermal discharge from the Cleft Segment, which has discharge brine-dominated, hydrothermal fluids from the same seafloor features for at least 32 years. In addition, the investigators will measure discharge temperatures, deploy and recover short-term continuous fluid samplers, and deploy temperature recorders for legacy studies. Results from a shore-based fluid characterization program will address the long-term stability, connectivity, and potential changes in subsurface, segment-scale processes within brine-dominated hydrothermal systemsThis 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.