Collaborative Research: Heat flow mapping and quantification at ASHES hydrothermal vent field using an observatory imaging sonar

热量从地球内部进入海洋是影响海洋动力学、化学交换和海洋生命的关键因素。然而，到目前为止，还不可能在很长一段时间内实时监测从海底热液喷口喷出的流体，尽管这些流体将大量内部地热从洋壳深处带到海底。这个项目克服了这个问题，办法是在国家科学基金会最近完成的海洋观测倡议的有线观测站上安装了新测试的仪器--有线观测站喷口成像声纳系统，该系统能够对热液喷口流体通量进行长期监测，该观测站位于胡安德富卡山脊Axial火山口的灰烬热液场。该声纳系统设计用于对热液排放和通过该排放从海底进入海洋的测量热量进行成像。这项工作的目标之一是继续改进该系统，并将其发展成为利用声波传感对热液活动(流体流动和热传输)进行长期重复量化的可靠工具。由此产生的热传输测量将能够调查向周围岩石提供热量的火山系统、地下流体流动过程和生物系统之间的联系，这些生物系统依赖于因地下水-岩石相互作用而产生的金属和其他化合物的淋滤而从热液系统发出的减少的化学物种。电缆声纳系统的第二次部署将测试其测量和耦合放电率和热传输的能力。这项工作的更广泛影响包括增加科学和应用基础设施，这些基础设施延伸到监测和测量甲烷渗漏处的甲烷排放速度和/或深水地平线等油井口井喷的石油排放速度。这项工作还将导致本科生的培养和教育与研究的结合。结果也将通过讲座和媒体向公众传播。研究地质-生物-热液耦合系统所需的最重要的现场测量之一是热通量。这是海底热液系统的一个基本特性。它将其驱动力(如火山岩浆或蛇纹岩作用等海底下热源)与其影响的系统联系起来，例如化学物质流入海洋。它还对次表层和表层生物圈施加控制。以前对海底热液热流进行适当测量的尝试无法用解决喷发动力学所需的综合空间/时间复盖面和分辨率来测量它。最近开发和测试的声纳系统将安装在国家科学基金会最近委托的海洋观测站倡议在胡安德富卡山脊灰烬热液喷口场地的电缆阵列上，这将使监测和量化热液排放及其从海底岩石转移到海洋的热量成为可能。声纳系统能够在喷口区域的很大范围内进行天气测量，并可以收集和传输长达数年的数据。这大大减少了在数据中进行外推的需要。除了监测之外，这项研究还将利用一种创新的声学数据反演方法，使用新开发的声学方法来估计通风口周围扩散流的热通量。该仪器的部署将为期4年。它将与地面真实测量相结合，以确定聚焦和扩散流的流速以及温度/热通量方面的声学结果的准确性。由此得到的聚焦热源和扩散热源的热流时间序列具有广泛的适用性。特别是，热流量值和变化对灰烬中的热液喷发动力学及其与地震活动、岩浆供应、地壳冷却和玄武岩-水相互作用的联系具有重要意义。它还对海洋的热量和化学变化、海底生态系统的能量和营养供应以及地下生物圈的范围和性质产生影响。

The movement of heat from inside the Earth into the ocean is a key factor influencing ocean dynamics, chemical exchange, and life in the oceans. However, until now, it has not been possible to monitor, in real time and over long periods of time, the fluids venting from seafloor hydrothermal vents even though these fluids carry a significant amount of internal geothermal heat from deep in the ocean crust to the seafloor. This project overcomes this problem by installing newly tested instrumentation, a Cabled Observatory Vent Imaging Sonar system, capable of long term monitoring of hydrothermal vent fluid fluxes, on the National Science Foundation's recently completed Ocean Observing Initiative's cabled observatory at the ASHES hydrothermal field in the caldera of Axial Volcano on the Juan de Fuca Ridge. This sonar system is designed for imaging hydrothermal discharge and the measuring heat transferred by that discharge into the ocean from the subseafloor. One goal of the work is to continue improving the system and developing it into a reliable tool for long-term repeated quantification of hydrothermal activity (fluid flow and heat transport) using acoustic sensing. The resulting heat transport measurements will enable investigation of the connections between the volcanic system, which supplies heat to the surrounding rock; subsurface fluid flow processes; and the biological systems that depend on the reduced chemical species that emanate from the hydrothermal system as a result of the leaching of metals and other compounds from water-rock interaction in the subsurface. This second deployment of the cabled sonar system will test its ability to measure and couple discharge rates and heat transport. Broader impacts of the work include increasing infrastructure for science and applications that extend to monitoring and measuring the discharge rates of methane at methane seeps and/or oil at oil-well head blowouts such as Deep Water Horizon. The work will also result in the training of undergraduates and the integration of education and research. Results will also be disseminated to the public via lectures and media outlets. One of the most important field measurements needed for the study of coupled geo-bio-hydrothermal systems is heat flux. This is a fundamental property of seafloor hydrothermal systems. It connects its driving force (i.e., sub-seafloor heat sources such as volcanic magma or serpentinization) to the systems it impacts, such as the flux of chemicals into the ocean. It also exerts controls on the subsurface and surface biosphere. Previous attempts to adequately measure seafloor hydrothermal heat flux have been unable to measure it with the combined spatial/temporal coverage and resolution necessary to resolve the dynamics of venting. The installation of the recently developed and tested sonar system that will be installed on the National Science Foundation's recently commissioned Ocean Observatory Initiative cabled array at the ASHES hydrothermal vent field on the Juan de Fuca Ridge will enable the monitoring and quantification of hydrothermal discharge and the heat transferred by it from rocks below the seafloor to the ocean. The sonar system is able to make synoptic measurements across a significant areal extent of the vent field and can collect and transmit data for periods of up to several years. This greatly reduces the need for extrapolation in the data. In addition to the monitoring, this research will exploit an innovative method for inversion of acoustic data to estimate the heat flux of diffuse-flow around the vents using a newly developed acoustic method. Deployment of the instrument will be for 4 years. It will be combined with ground-truth measurements to establish the accuracy of the acoustic results in terms of flow rates for focused and diffuse flow and for temperature/heat flux. The resulting time series for heat flux from focused and diffuse sources has a broad range of applicability. In particular, heat flux values and variations have implications for the dynamics of hydrothermal venting at ASHES and its connections with seismicity, magma supply, crustal cooling, and basalt-water interactions. It also exerts influence on heat and chemical changes in the ocean, energy and nutritive supplies to seafloor ecosystems; and the extent and nature of the subsurface biosphere.