Developing a Global Listening Network for Turbidity Currents and Seafloor Processes

我们的总体目标是通过开发和展示新型传感器系统，在了解海底过程和危害方面实现根本性的逐步改变，这些传感器系统可以形成广泛和长期的监听网络。这些低成本和高能效的传感器包括水听器（水柱中的声学噪声）和地震检波器（地面震动）。数据将通过弹出式浮标和卫星链路返回，这是非常成功的Argo项目在水柱剖面方面所开创的。这种低成本网络可能会有不同寻常的广泛应用，用于警告对宝贵的海底基础设施的威胁，监测CCS设施或天然气管道的泄漏，或用于海啸预警系统。在这里，我们的目标是回答有关如何触发海底质量流（浊流和滑坡）的基本问题，然后表现。这些危险且通常强大（2-20米/秒）的海底事件形成了我们星球上最大的沉积物堆积，最深的峡谷和最长的通道系统。湍流可以延伸数百至数千公里，破坏承载全球95%以上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向深海转移以及地球化学循环方面发挥着全球重要作用;同时其沉积物在全球范围内拥有宝贵的石油和天然气储量。众所周知，海底物质流很难在实际中测量，与它们的陆上兄弟相比，测量很少。这意味着在关于海底物质流如何被触发、它们的频率和跳动以及它们如何表现的基本理解方面存在根本性的差距。最近的监测已经取得了进展，使用功耗（有源）传感器，如声学多普勒电流剖面仪（ADCP）。但是有源传感器有很大的缺点，不能在全球范围内部署。它们只能进行短时间的测量，位于锚定在这些强大的水流中的系泊设备上（通常会将昂贵的系泊设备和传感器带走），并且它们需要多个周期的昂贵研究船进行部署和回收。因此，我们将设计、建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。这些新的传感器将记录质量流的时间和触发;和前端速度的变化（通过渡越时间），和流功率（通过声学或振动信号的强度）。我们将首先确定如何最好地记录水下质量流水听器和地震检波器，以及如何记录随流速和类型，或传感器的距离变化。我们在三个地点的初步工作已经表明，水听器和地震检波器确实记录了质量流。在这里，我们将确定捕获质量流量信号的最佳方法，并将其与其他过程区分开来。这项工作将成为设计新一代低成本（<5000英镑）智能传感器的基础，这些传感器无需昂贵的水面船只即可通过弹出式浮标和卫星链路返回数据。技术的进步使这一项目及时，因为它们允许智能水听器或地震检波器进行机载数据处理，以减少数据量，这些数据量可以被触发以更高的频率进行短时间记录。我们将实地测试新的智能传感器，从而展示它们如何回答主要的科学问题。我们试图了解是什么触发了海底流动，以及这种初始触发机制如何影响流动行为。特别是，海底水流如何与危险的河流洪水、风暴或地震联系在一起，因此它们如何记录这些危险？不同环境下的海底水流是否表现出一致的行为模式，如果不是，是什么导致了这些差异？为此，我们将沿着台湾近海的刚果峡谷（稀释河，被动边缘，无气旋）部署这些新的传感器。

Our overall aim is to make fundamental step-changes in understanding of seafloor processes and hazards by developing and demonstrating novel sensor systems, which can form widespread and long-term listening networks. These low-cost and energy-efficient sensors comprise hydrophones (acoustic noise in water column) and geophones (ground shaking). Data will be returned via pop-up floats and satellite links, as has been pioneered by the highly successful Argo Project for water-column profile.This type of low-cost network could have unusually widespread applications for warning against threats to valuable seabed infrastructure, monitoring leaks from CCS facilities or gas pipelines, or for tsunami warning systems. 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 work will form the basis for designing a new generation of low-cost (< £5k) smart sensors that 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 or geophones to reduce data volumes, which can be triggered to record for short periods at much higher frequency. We will field-test the new smart sensors, and thus demonstrate how they can answer major science questions. We seek to understand what triggers submarine flows, and how this initial trigger mechanism affects flow behaviour. In particular, how are submarine flows linked to hazardous river floods, storms or earthquakes, and hence how do they record those hazards? Do submarine flows in diverse settings show consistent modes of behaviour, and if not, what causes those differences? To do this, we will deploy these new sensors along the Congo Canyon (dilute river, passive margin, no cyclones) offshore Taiwan.