Energy and Environment Institute, University of Hull, Hull, HU6 7RX, UK.
School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK.
Nat Commun. 2019 Mar 27;10(1):1381. doi: 10.1038/s41467-019-09254-2.
Gravity currents are the primary means by which sediments, solutes and heat are transported across the ocean-floor. Existing theory of gravity current flow employs a statistically-stable model of turbulent diffusion that has been extant since the 1960s. Here we present the first set of detailed spatial data from a gravity current over a rough seafloor that demonstrate that this existing paradigm is not universal. Specifically, in contrast to predictions from turbulent diffusion theory, self-sharpened velocity and concentration profiles and a stable barrier to mixing are observed. Our new observations are explained by statistically-unstable mixing and self-sharpening, by boundary-induced internal gravity waves; as predicted by recent advances in fluid dynamics. Self-sharpening helps explain phenomena such as ultra-long runout of gravity currents and restricted growth of bedforms, and highlights increased geohazard risk to marine infrastructure. These processes likely have broader application, for example to wave-turbulence interaction, and mixing processes in environmental flows.
重力流是沉积物、溶质和热量在海底传输的主要方式。现有的重力流流动理论采用了自 20 世纪 60 年代以来一直存在的统计稳定的湍流扩散模型。在这里，我们首次提供了一组详细的海底粗糙重力流的空间数据，证明了这一现有范式并非普遍适用。具体来说，与湍流扩散理论的预测相反，观察到了自锐化速度和浓度分布以及稳定的混合障碍。我们的新观测结果可以通过统计不稳定混合和自锐化、边界诱导的内重力波来解释；这是最近流体动力学进展的预测。自锐化有助于解释重力流超长的运行距离和床形的限制生长等现象，并突出了海洋基础设施面临的地质灾害风险增加。这些过程可能具有更广泛的应用，例如波浪-湍流相互作用以及环境流动中的混合过程。
