First detailed synchronous sediment-concentration and velocity data for submarine turbidity currents

海底沉积物密度流(“浊流”)和陆地上的河流是在地球上移动沉积物的最重要的体积过程。然而，与河流洪水相比，海底水流更具间歇性，通常也更猛烈(流速高达20米/S)。此外，一条海底水流能够输送十倍于世界所有河流年泥沙总和的泥沙。海底流动之所以重要，是因为它们产生了许多世界上最广泛、最大量的沉积矿床，无论是在现代海底还是在古代岩石记录中都是如此，但也因为它们可以破坏海底电缆，这些电缆现在承载着95%以上的全球数据流量(通过互联网和金融市场支撑我们的日常生活)。古老的海底流创造了地下岩层，其中包含了我们许多最大的石油和天然气储量。海底水流将比大峡谷更深的峡谷雕刻成比大峡谷更深的峡谷，而峡谷内的水流在向深海底栖生态系统(包括重要的多样性热点)提供有机碳和营养物质方面发挥着关键作用。海底密度流最显著的方面是，它们很难直接监测，而且我们目前对此类水流的实际观测是如此之少。这种缺乏直接观测的情况与其他主要泥沙输送过程所能获得的信息形成鲜明对比。仅在五个地点测量了海底水流前沿速度的变化，主要是通过水下电缆连续断裂的时间提供的间接证据。它们的垂直速度剖面只在三个地点测量过，而且从未以每小时一个以上的采样频率进行过测量。没有任何流动沿着其完整的路径被监测到，这一点非常重要，因为沿着该路径流动的特征发生了相当大的演变。为了使我们对海底流动的理解发生根本的变化，我们需要直接监测沿其整个流动路径的活跃流动。在此之前，我们对流动特征及其空间演变的了解仍将是有限的。该项目将提供迄今为止收集到的关于海底流动的最详细监测数据：第一个对稀薄和稠密近底流组分施加限制的数据，第一个跨越整个流动路径的数据集，以及第一个将这种环境中流动过程的测量和由此产生的沉积特征联系起来的数据集。我们的目标是与蒙特利湾水族馆研究所(MBARI)和美国地质调查局(USGS)合作，开展一个大规模的合作项目，记录和了解2014-16年18个月期间加州近海蒙特利峡谷内发生的沉积物输送过程。这种国际合作对于分摊这项雄心勃勃的工作的成本至关重要。MBARI为该项目提供了一系列用于监测流量的创新工具，这些工具是MBARI在过去十年中设计、建造和现场测试的；这笔捐款价值超过1000万美元。这包括蒙特利海洋观测系统的海底仪器节点，该系统将首次高频(每2至30秒而不是每小时一次)测量这种流动的三维速度、温度、盐度和密度分布。MBARI还提供在这18个月期间进行设备部署和维修所需的考察船和ROV，因为MBARI位于峡谷的顶部。MBARI和USGS将在峡谷放置更多的监测设备，作为该项目的一部分，该项目价值150万美元。此外，MBARI和USGS承担其所有设备损失的风险。NERC承担了这项独特的现场实验总成本和风险的一小部分，因此代表着非凡的性价比。

Submarine sediment density flows ("turbidity currents") and rivers on land are volumetrically the most important processes for moving sediment across our planet. However, submarine flows are more episodic and are typically more violent (with speeds of up to 20m/s) than river floods. Moreover, a single submarine flow is capable of transporting ten times the annual sediment load from all of the world's rivers combined. Submarine flows are important because they produce many of the world's most extensive and voluminous sedimentary deposits, both on the modern sea floor and in the ancient rock record, but also because they can break seafloor cables that now carry over 95% of global data traffic (that underpin our daily lives through the internet and financial markets). Ancient submarine flows created subsurface rock sequences that contain many of our largest oil and gas reserves. Submarine flows carve canyons, which are deeper than the Grand Canyon, through processes that are still poorly understood, and flows within canyons play a key role in supplying organic carbon and nutrients to benthic ecosystem (that include important diversity hotspots) in the deep sea.The most remarkable aspect of submarine density flows is how difficult they are to monitor directly, and how few observations we presently have of such flows in action. This paucity of direct observation provides a stark contrast to the information available for other major sediment transport processes. Changes in the frontal speed of submarine flows have been measured in just five locations, mainly through indirect evidence provided by the timing of sequential underwater cable breaks. Their vertical velocity profile has only ever been measured in three locations and never with sampling rates more frequent than one per hour. No flow has been monitored along its full path, which is of key importance because flows evolve considerably in character along that path.To produce a fundamental step-change in our understanding of submarine flows we need to directly monitor active flows along their entire flow path. Until this is achieved, our understanding of the flow character and its spatial evolution will remain limited. This project will provide by far the most detailed monitoring data yet collected for submarine flows: be the first that places constraints on both dilute and dense near-bed flow components, be the first data set that spans the full flow path, and be the first data set to link measurements of flow processes and the resulting deposit character in such an environment. We aim to conduct a large-scale collaborative program to document and understand sediment transport processes occurring within Monterey Canyon offshore California during an 18-month period in 2014-16, in collaboration with the Monterey Bay Aquarium Research Institute (MBARI) and US Geological Survey (USGS). Such international collaboration is essential for spreading the cost of this ambitious work. MBARI are providing the project with access to a series of innovative tools for monitoring flows that MBARI have designed, built and field tested over the last decade; a contribution worth over $10 Million. This includes aBenthic Instrument Nodes for their Monterey Ocean Observing System that will provide the first high frequency (every 2 to 30 seconds rather than hourly) measurements of 3D velocity, temperature, salinity and density profiles from such flows. MBARI also provide access to the research vessels and ROVs necessary for equipment deployment and servicing during this 18 month period, as MBARI is located at the head of the canyon. MBARI and USGS will place further monitoring equipment in the canyon as part of the project that is worth a further $1.5 Million. Moreover, the MBARI and USGS bear the risk for the loss of all of their equipment. NERC bears a small fraction of the total cost and risk for this unique field experiment, which therefore represents exceptional value for money.