FLOW PARAMETERS OF TURBIDITY CURRENTS IN A LOW-SINUOSITY GIANT DEEP-SEA CHANNEL

Flow parameters (velocity and density) for turbidity currents in the N orthwest Atlantic Mid-Ocean Channel (NAMOC) have been determined based on two different approaches, channel geometry and grain-size distribu tions of turbidites. Channel geometry has been obtained by a quantitat ive morphological analysis of the NAMOC which shows three genetically different segments in the upper 2000 km: (1) an upper 350 km-long 'equ ilibrium channel', (2) a middle 700 km-long 'modified equilibrium chan nel' and (3) a lower 'basement-controlled channel' which is more than 1000 km-long. In contrast to other meandering submarine channels the N AMOC has very low sinuosities and gradients. A consistently higher rig ht-hand levee limits mean flow velocities to 3 m s(-1) and channel geo metry indicates mean flow velocities of 0.86 m s(-1) that decrease wit hin 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 stro ng vertical gradients results in a decoupling of the current head and body. Channel geometry appears to be mainly the result of the slowly m oving dilute body of the current.