FLOW AND PARTICLE MOTION-INDUCED ABOVE A TALL SEAMOUNT BY STEADY AND TIDAL BACKGROUND CURRENTS

The response of a stratified ocean over a tall, isolated seamount indu ced by the combination of slow, steady, spatially uniform inflow and w eak diurnal tides is examined using a primitive-equation numerical mod el. Steady inflow alone forms a Taylor cap, which retains Lagrangian f luid particles over the seamount for a duration that scales inversely with the mean inflow speed (U) over bar over the range (U) over bar/fL = 0.004-0.036, where f is the Coriolis parameter and L is the horizont al length scale of the seamount. Fluid particles located at mid-depth and shallower over the top of the seamount are retained for up to abou t five advective time scales (L/(U) over bar). Near-bottom particles m ay be retained much longer. Tidal forcing alone drives a seamount-trap ped wave that gives rise, through non-linear rectification, to a botto m-intensified time-mean circulation around the rim of the seamount. Th e magnitude of the rectified mean current varies approximately linearl y with the tidal amplitude U-0 over the range U-0/fL=(1.08-3.60)x 10(- 3). The seamount-trapped wave scatters particles vertically over the s eamount summit, producing net displacements over many tidal cycles of 100-300 m. The combination of both forcings produces a near superposit ion of the two separate responses. The tide hardly affects particle re tention by the steady inflow, except near the bottom, where retention is enhanced by the bottom-intensified rectified mean flow. The steady inflow hardly affects the vertical scattering of particles by the tide , except by altering the duration for which particles remain over the seamount and are thereby subject to vertical scattering. (C) 1997 Else vier Science Ltd.