Mixing and transport near the shallow-crested Rumble III seamount and the implications for plankton distribution

Abstract

Vessel-based observations of water column structure and flow near a shallow-crested seamount are used to quantify the physical disturbance induced by that seamount. The implications of this disturbance on the feeding hole hypothesis are then examined based on data from moored thermistors and acoustic current profilers, as well as vessel-based acoustic sounding-derived biomass estimates, currents, and conductivityerature-depth profiles from a 55 km square grid of stations around the crest. Mean currents in the region of 0.2 m s -1 are comparable to observations from surface drifters whereas the semidiurnal tidal flow amplitude was one third of this. Thorpe Scale-based estimates of energy dissipation rate were in the range 10-9 to 2.10-8 W kg-1 and vertical diffusivities Kz were in the range 10-4 to 10-3 m2 s-1. Turbulence levels were higher upstream of the seamount-likely due to the influence of nearby seamounts Rumble IV and V. There was no evidence of a Taylor Cap in the Rumble III velocity field. The sounder data provide some evidence of a feeding hole and analysis based on diffusivities suggests that this might persist downstream of the seamount for as much as 7 days. © 2014 The National Institute of Water and Atmospheric Research.