Flow parameters of turbidity currents in a low-sinuosity giant deep-sea channel

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ABSTRACT

Flow parameters (velocity and density) for turbidity currents in the Northwest Atlantic Mid-Ocean Channel (NAMOC) have been determined based on two different approaches, channel geometry and grain-size distributions of turbidites. Channel geometry has been obtained by a quantitative morphological analysis of the NAMOC which shows three genetically different segments in the upper 2000 km: (1) an upper 350 km-long ‘equilibrium channel’, (2) a middle 700 km-long ‘modified equilibrium channel’and (3) a lower ‘basement-controlled channel’which is more than 1000 km-long. In contrast to other meandering submarine channels the NAMOC has very low sinuosities and gradients. A consistently higher right-hand levee limits mean flow velocities to 3ms−1 and channel geometry indicates mean flow velocities of 0·86 m s−1 that decrease within the equilibrium channel to 0·05 m s−1. Grain-size distributions on the levees and in the channel suggest strong vertical velocity and density gradients for bank-full flows with velocities of up to 8 m s−1 and excess densities up to 87 kg m−3 at the base, and 0·45 m s−1 and 4 kg m−3 at the top. The internal shear produced by these strong vertical gradients results in a decoupling of the current head and body. Channel geometry appears to be mainly the result of the slowly moving dilute body of the current.

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