Developing a Global Listening Network for Turbidity Currents and Seafloor Processes

这个雄心勃勃的项目可以通过开发一个基于低成本水听器（通过水柱中的声学噪声）和地震检波器（通过地面震动）的监听网络，在了解海底过程和地质灾害方面取得重大进展。这种类型的低成本网络有着不同寻常的广泛应用，但在这里，我们的目标是回答关于海底质量流（浊流和滑坡）是如何触发的，然后是如何表现的基本问题。这些危险而强大的海底活动（2-20米/秒）形成了地球上最大的沉积物堆积、最深的峡谷和最长的水道系统。浊流可以绵延数百到数千公里，破坏承载全球95%数据流量的海底电缆网络，包括互联网和金融市场，或战略石油和天然气管道。这些流动在有机碳和营养物质向深海的转移以及地球化学循环中发挥着全球性的重要作用；同时，他们的矿藏在世界范围内拥有宝贵的石油和天然气储量。众所周知，海底物质流很难测量，与陆地上的物质流相比，海底物质流的测量数据很少。这意味着，对于海底物质流是如何被触发的，它们的频率和跳动，以及它们的行为，在基本的理解上存在根本性的差距。最近的监测在使用耗电（有源）传感器（如声学多普勒电流分析器（ADCPs））方面取得了进展。但是有源传感器有很大的缺点，不能全局部署。它们只能在很短的时间内进行测量，并且位于锚定在这些强大水流中的系泊处（通常会带走昂贵的系泊和传感器），而且它们需要花费大量时间来部署和回收昂贵的研究船。因此，我们将设计、制造和测试能够以低得多的成本部署在广泛地区的无源传感器。这些新型传感器将记录质量流量定时和触发器；以及前转速（通过时间）和流功率（通过声音或振动信号的强度）的变化。我们将首先确定水听器和检波器如何最好地记录海底质量流，以及该记录如何随流速、类型或与传感器的距离而变化。我们在三个地点的初步工作已经表明，水听器和检波器确实记录了质量流。在这里，我们将确定捕获质量流信号的最佳方法，并将其与其他过程区分开来。这将为设计和现场测试新一代低成本智能传感器奠定基础，这些传感器无需昂贵的水面船只即可返回数据；通过弹出式花车和卫星链接。技术的进步使这个项目变得及时，因为它们允许智能水听器在船上处理数据，以减少数据量，可以触发以更高的频率记录短时间。我们将测试新的智能传感器，并用它们来回答两个主要的科学问题。首先，不同环境下的海底水流是否表现出一致的行为模式？其次，是什么触发了河流补给系统的海底流动，它们与主要的河流洪水、地震和热带气旋有何联系？为了做到这一点，我们将沿着西非的刚果峡谷（稀释河，被动边缘，没有气旋）和台湾的高平峡谷（高旋河，活跃边缘，频繁气旋）放置这些新的传感器。这些传感器还有其他广泛的应用。低成本的预警传感器将是海上危害评估、CCS设施或天然气管道泄漏的重大进步。记录山体滑坡的传感器将对海啸预警系统或对宝贵的海底基础设施的威胁产生重大影响。这个建议也特别及时，因为技术的进步现在允许车载数据处理和智能传感器之间的通信，可以以更高的频率触发短时间的记录。

This ambitious project can make a major step-change in understanding of seafloor processes and geohazards by developing a listening network based on low-cost hydrophones (via acoustic noise in water column) and geophones (via ground shaking). This type of low-cost network has unusually widespread applications, but here we aim to answer fundamental questions about how submarine mass-flows (turbidity currents and landslides) are triggered, and then behave. These hazardous and often powerful (2-20 m/s) submarine events form the largest sediment accumulations, deepest canyons, and longest channel systems on our planet. Turbidity currents can runout for hundreds to thousands of kilometres, to break seabed cable networks that carry >95% of global data traffic, including the internet and financial markets, or strategic oil and gas pipelines. These flows play a globally important role in organic carbon and nutrient transfer to the deep ocean, and geochemical cycles; whilst their deposits host valuable oil and gas reserves worldwide. Submarine mass flows are notoriously difficult to measure in action, and there are very few measurements compared to their subaerial cousins. This means there are fundamental gaps in basic understanding about how submarine mass flows are triggered, their frequency and runout, and how they behave. Recent monitoring has made advances using power-hungry (active source) sensors, such as acoustic Doppler current profilers (ADCPs). But active-source sensors have major disadvantages, and cannot be deployed globally. They can only measure for short periods, are located on moorings anchored inside these powerful flows (which often carry the expensive mooring and sensors away), and they need multiple periods of expensive research vessels to be both deployed and recovered. We will therefore design, build and test passive sensors that can be deployed over widespread areas at far lower cost. These novel sensors will record mass-flow timing and triggers; and changes in front speed (from transit times), and flow power (via strength of acoustic or vibration signal).We will first determine how submarine mass flows are best recorded by hydrophones and geophones, and how that record varies with flow speed and type, or distance to sensor. Our preliminary work at three sites already shows that hydrophone and geophones do record mass-flows. Here we will determine the best way to capture that mass-flow signal, and to distinguish it from other processes. This will form the basis for then designing and field testing a new generation of low-cost smart sensors, which return data without expensive surface vessels; via pop-up floats and satellite links. Advances in technology make this project timely, as they allow on-board data processing by smart hydrophones to reduce data volumes, which can be triggered to record for short periods at much higher frequency. We will test the new smart sensors, and use them to answer two major science questions. First, do submarine flows in different settings show consistent modes of behaviour? Second, what triggers submarine flows in river-fed systems, and how are they linked to major river floods, earthquakes, and tropical cyclones? To do this, we will place these new sensors along the Congo Canyon (dilute river, passive margin, no cyclones) off West Africa, and the Gaoping Canyon (hyperpycnal river, active margin, frequent cyclones) offshore Taiwan.These sensors have other widespread applications. Low cost warning sensors would be a major advance for offshore hazard assessment, and leaks from CCS facilities or gas pipelines. Sensors that record landslides would be a step change for tsunami warning systems, or threats to valuable seabed infrastructure. This proposal is also particularly timely, because of advances in technology now allow on-board data processing and communication between smart sensors, which can be triggered to record for short periods at much higher frequency.