Abstract:

This study theoretically explores sediment fluxes of high-density mud suspensions across the seafloor under the assumption that the dispersions received their entire sediment load from local resuspension of surface mud. Flocculation is ignored, and a constant maximum floccule size is prescribed. The resultant sediment-flux equation, which constitutes a bottom-boundary condition for use in suspended-sediment models, has important physical implications. First, this study identifies a condition, referred to as gelling ignition, in which sediment concentrations will increase to extremely large values owing to a positive feedback between net erosion and hindered settling. Remarkably, this work reveals that, owing to boundary-layer dynamics, mud suspensions of both low and high concentrations are easier to keep in suspension than those of intermediate concentrations. Wave conditions in which high concentrations are produced in the model are within the realm of those typical of storms on shelves. On a sloping shelf, these highly concentrated suspended mud layers would be driven down slope by gravity, and thus represent a possible mechanism for cross-shelf transport.

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