Self-sharpening induces jet-like structure in seafloor gravity currents

• Published in: Nature communications Vol. 10; no. 1; p. 1381
• Main Authors: Dorrell, R. M., Peakall, J., Darby, S. E., Parsons, D. R., Johnson, J., Sumner, E. J., Wynn, R. B., Özsoy, E., Tezcan, D.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 27.03.2019; Nature Publishing Group; Nature Portfolio
• Subjects: 704/2151/215; 704/829/2737; Computational fluid dynamics; Data processing; Diffusion barriers; Diffusion theory; Eddy diffusion; Fluid dynamics; Fluid flow; Geological hazards; Gravitational waves; Gravity waves; Humanities and Social Sciences; Hydrodynamics; Mixing processes; multidisciplinary; Ocean floor; Predictions; River beds; Science; Science (multidisciplinary); Sedimentary structures; Sediments; Sharpening; Solutes; Spatial data; Turbulence; Turbulent diffusion
• DOI: 10.1038/s41467-019-09254-2
• ISSN: 2041-1723

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. The current paradigm of material transport across the ocean-floor by gravity currents, is of turbulent flows with mixing processes analogous to rivers. However, uniquely high-resolution field data demonstrate that this paradigm is flawed and that gravity currents are analogous to self-organised atmospheric jets.