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，人们还不可能长时间实时监测海底热液喷口喷出的液体，尽管这些液体将大量的内部地热从海洋地壳深处带到海底。这个项目克服了这个问题，在美国国家科学基金会最近完成的海洋观测倡议的电缆观测站安装了新测试的仪器，一个电缆观测站喷口成像声纳系统，能够长期监测热液喷口的流体通量。该观测站位于胡安德富卡山脊轴向火山火山口的灰烬热液区。这种声纳系统是为热液排放成像而设计的，并测量热液从海底排放到海洋中的热量。这项工作的一个目标是继续改进该系统，并将其发展成为一种可靠的工具，用于利用声学传感长期重复量化热液活动（流体流动和热输送）。由此产生的热输运测量将有助于研究火山系统之间的联系，火山系统为周围的岩石提供热量；地下流体流动过程；生物系统依赖于从热液系统中释放的化学物质的减少，这些化学物质是地下水岩相互作用中金属和其他化合物的浸出的结果。电缆声呐系统的第二次部署将测试其测量和耦合放电速率和热传输的能力。这项工作的更广泛影响包括增加科学基础设施和应用，扩展到监测和测量甲烷渗漏和/或石油井口井喷（如深水地平线）的甲烷排放率。这项工作还将导致本科生的培训和教育与研究的结合。研究结果也将通过讲座和媒体传播给公众。热通量是研究地球-生物-热液耦合系统所需要的最重要的野外测量之一。这是海底热液系统的一个基本特性。它将其驱动力（即火山岩浆或蛇纹石化等海底热源）与它所影响的系统（如化学物质流入海洋）联系起来。它还对地下和地表生物圈施加控制。以前对海底热液热通量进行充分测量的尝试，无法以解决喷发动力学所必需的综合时空覆盖和分辨率对其进行测量。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倡议电缆阵列上，该阵列位于Juan de Fuca Ridge的ASHES热液喷口场，将能够监测和量化热液排放以及热液从海底以下岩石传递到海洋的热量。声纳系统能够在火山口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。这大大减少了对数据外推的需要。除了监测外，本研究还将探索一种创新的声学数据反演方法，利用新开发的声学方法估计喷口周围扩散流的热通量。该仪器的部署将持续4年。它将与地面真值测量相结合，以确定在聚焦和扩散流动以及温度/热通量方面声学结果的准确性。所得的集中源和漫射源的热通量时间序列具有广泛的适用性。特别是，热通量值和变化对灰烬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。它还对海洋中的热量和化学变化、对海底生态系统的能源和营养供应产生影响；以及地下生物圈的范围和性质。

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.