Quantifying the journey of a turbidity current: How water and sediment discharges vary with distance in Monterey Canyon
Quantifying the journey of a turbidity current: How water and sediment discharges vary with distance in Monterey Canyon
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量化浊流的行程：蒙特利峡谷的水和沉积物排放量如何随距离变化
DOI：
10.1002/essoar.aa5f1fcca6199cef.78cd1656f4de4034.1
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Chapplow N
中科院分区：
文献类型：
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作者：
Chapplow N
浑浊流在海底运输着大量的沉积物，形成了地球上最大的沉积物堆积。这些流动对具有重要战略意义的海底基础设施构成威胁，同时也是运输支持深海生态系统的有机碳和营养物质的重要媒介。因此，量化这些流的规模、输沙量以及流量随时间和空间的演变是很重要的。在实验和数值模型的基础上提出了两种流动演化模式。第一种被称为点火，水流带着海底沉积物，变得更大、更强大，并增加了它们的排放量。在称为耗散的第二种演化模式中，泥沙脱离悬浮状态，因此水流减速并失去流量。到目前为止，野外尺度的浊度流只在世界范围内的少数几个地点进行了测量，从未在多个地点进行过详细的全程测量。因此，尚不可能确定深海中的水流何时、何地以及为何会分化成这两种模式，也不可能确定水流的流量是如何变化的。这项雄心勃勃的多机构联合峡谷实验在加州近海蒙特雷峡谷的七个仪器系泊处测量了浊度流。记录了15次流动，包括迄今为止在高分辨率下测量到的最快的流动（bbb8 m/s）。这一显著的数据集首次提供了量化深海浑浊流下游沉积物和流量演变的机会。为了了解水流是点燃还是消散，我们得出了峡谷中所有七个系泊地点每条水流的总流量和沉积物排放量。根据测量的流速计算出流量，并使用一种新的反演方法推导出泥沙浓度。我们观察到两种不同的流动模式，大多数流动在峡谷上游迅速消散，而三种流动在整个50公里的阵列长度上消失。然后，我们探讨了为什么只有这三种水流被点燃，并讨论了对峡谷和河道容量和演化的影响。
Turbidity currents transport vast quantities of sediment across the seafloor and form the largest sediment accumulations on Earth. These flows pose a hazard to strategically important seafloor infrastructure and are important agents for the transport of organic carbon and nutrients that support deep-sea ecosystems. Therefore, it is important to quantify the scale of these flows, the amount of sediment they transport, and the evolution of their discharge over time and space along their flow path. Two modes of flow evolution have been proposed based on experimental and numerical models. The first is termed ignition, where flows entrain seafloor sediment, becoming more voluminous and powerful and increasing their discharge. In the second mode of evolution, called dissipation, sediment falls out of suspension, so flows decelerate and lose discharge. Thus far, field-scale turbidity currents have only been measured at a handful of sites worldwide, and never in detail at multiple locations along their full course. Therefore, it has not yet been possible to determine when, where, and why flows diverge into these two modes in the deep sea, or how flow discharge varies. The ambitious multi-institution Coordinated Canyon Experiment measured turbidity currents at seven instrumented moorings along the Monterey Canyon, offshore California. Fifteen flows were recorded, including the fastest events yet measured at high resolution (>8 m/s). This remarkable dataset provides the first opportunity to quantify down-channel sediment and flow discharge evolution of turbidity currents in the deep sea. To understand whether flows ignite or dissipate, we derive total and sediment discharges for each of the flows at all seven mooring locations down the canyon. Discharges are calculated from measured velocities, and sediment concentrations are derived using a novel inversion method. We observe two distinct flow modes, as most flows rapidly dissipated in the upper reaches of the canyon, while three ran out for the full 50 km array length. We then explore why only these three flows ignited and discuss the implications for canyon and channel capacity and evolution.