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

合作研究：阐明胡安德富卡海岭裂缝段沿线以盐水为主的分段规模热液排放

• 批准号: 2052584
• 负责人: Charles Wheat
• 金额: $ 38.71万
• 依托单位: University of Alaska Fairbanks Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-15 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2052584&HistoricalAwards=false
• 关键词: Collaborative; Research; Elucidating; Brine; Dominated

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.

胡安德富卡海脊上的热液盐水由注入海底的岩浆形成，然后通过海水循环冷却，这种热液循环在热岩石和海水之间交换热量和化学物质，从而产生矿物沉积和独特的海底注入生态系统。岩浆的分布与海底热循环和排出流体的成分一样不规则。在岩浆注入事件期间和之后，加热的海水分离成低盐度蒸气。缺乏许多溶解金属的阶段和富含高盐度金属的盐水阶段 蒸气的海底排放通常是短暂的（数年），随后是较长的阶段（数十年到数百年或更长时间）。在这项研究中，我们将对俄勒冈州海岸附近的胡安德富卡海岭裂隙部分的热液进行采样并分析其化学成分。 1986 年的一次岩浆事件，三十多年来一直在排放盐水，这些流体成分的系统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（数十年），描述溶解的输送。盐水相中的矿物质和气体，有助于我们了解地壳和海洋之间的元素交换。岩浆侵入洋壳会导致海水的热和化学变化。在海底排放之前，海洋岩石圈内的对流循环会影响海洋中的生物地球化学循环、海底富含金属矿藏的形成以及海底生态系统。净效应由热液活动的循环时间和空间演化决定。许多系统从短暂（数年）的气相排放开始，逐渐发展为相对较长的（数十年至数百年）的盐水相排放。对于以蒸汽为主的热液系统，对以盐水为主的系统的系统时间序列研究是有限的，因为岩浆驱动的海底热液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。持续几个世纪或更长时间，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来自裂缝段的热液排放。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，研究人员将测量排放温度，部署和恢复短期连续流体采样器，并部署温度记录仪以获取遗留研究结果。岸基流体表征计划将解决以盐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，并被认为值得通过评估获得支持利用基金会的智力优势和更广泛的影响审查标准。