Influence of Coriolis force upon bottom boundary layers in a large‐scale gravity current experiment: implications for evolution of sinuous deep‐water channel systems

Abstract

Oceanic density currents in many deep-water channels are strongly influenced by the Coriolis force. The dynamics of the bottom boundary layer in large geostrophic flows and low Rossby number turbidity currents are very important for determining the erosion and deposition of sediment in channelized contourite currents and many large-scale turbidity currents. However, these bottom boundary layers are notoriously difficult to resolve with oceanic field measurements or in previous small-scale rotating laboratory experiments. We present results from a large, 13-m diameter, rotating laboratory platform that is able to achieve both stratified and highly turbulent flows in regimes where the rotation is sufficiently rapid that the Coriolis force can potentially dominate. By resolving the dynamics of the turbulent bottom boundary in straight and sinuous channel sections, we find that the Coriolis force can overcome centrifugal force to switch the direction of near-bed flows in channel bends. This occurs for positive Rossby numbers less than +0.8, defined as Ro _R = (Formula presented.) /Rf, where (Formula presented.) is the depth and time-averaged velocity, R is the radius of channel curvature, and f is the Coriolis parameter. Density and velocity fields decoupled in channel bends, with the densest fluid of the gravity current being deflected to the outer bend of the channel by the centrifugal force, while the location of velocity maximum shifted with the Coriolis force, leading to asymmetries between left- and right-turning bends. These observations of Coriolis effects on gravity currents are synthesized into a model of how sedimentary structures might evolve in sinuous turbidity current channels at various latitudes.

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ORCID for S.E. Darby: orcid.org/0000-0001-8778-4394

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