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

胡安德富卡山脊上的热液卤水新的洋壳是由注入海底的岩浆形成的，然后通过海水循环冷却。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成分也是如此。在岩浆注入事件期间和之后，加热的海水分离为缺乏大量溶解金属的低盐度汽相和高盐度富金属卤水相。水蒸气在海底的排放通常是短暂的(几年)，然后是一个更长的阶段(几十年到几百年或更长)的卤水排放。目前关于卤水组成及其时空演化的知识有限。在这次调查中，沿俄勒冈州海岸胡安德富卡山脊裂隙段的热液流体将被取样并分析其化学成分。这部分年轻的洋壳在1986年经历了一次岩浆事件，30多年来一直在排放卤水。这些流体组成的系统变化将使我们能够记录以卤水为主的海底热液系统的长期(数十年)演化，表征卤水相中溶解矿物和气体的运移，并有助于我们了解地壳和海洋之间的元素交换。岩浆侵入大洋地壳，导致海水在海底排出之前，在大洋岩石圈内的对流循环中发生热和化学变化。这种热液排放影响了海洋中的生物地球化学循环、海底富金属矿藏的形成和海底生态系统。净效应是由热液活动的周期性时空演化决定的。许多系统开始时排放的是短寿命(数年)的蒸汽相，然后演变成寿命较长的(几十年到几百年甚至更长)的卤水相排放。相对于以蒸汽为主的热液系统，以卤水为主的系统时间序列研究是有限的。了解以卤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，这种以卤水为主的流体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。气密流体采样器将收集裂隙段的热液排放，裂隙段的排放以卤水为主，热液流体来自相同的海底地貌至少32年。此外，调查人员将测量排放温度，部署和回收短期连续流体采样器，并为遗留研究部署温度记录器。岸基流体表征计划的结果将解决以卤水为主的热液系统中地下、分段规模过程的长期稳定性、连通性和潜在变化。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。

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.