Downward flux of particulate organic matter and vertical distribution of calanoid copepods in the Oyashio water in summer

Abstract

A vertical flux profile in the upper 1000 m in the Oyashio Water was obtained using a free-drifting array with particle interceptors traps in June 1983. Vertical carbon flux was >100 mg m −2 day −1 in the upper 200 m and decreased to <60 mg m −2 day −1 below 500 m. One of the principal particles was fecal pellets, possibly derived from calanoid copepods. Diel distributions of copepods showed two marked levels of population density: 10–60 m (>600 inds m −3) and 215–320 m (160–600 inds m −3). All the dominant copepods except Metridia lucens (adult female) tended to stay more or less at fixed depth layers. Copepodites of some dominant species could not be found in the shallow phytoplankton-rich layer. Nevertheless, scanning electron microscope observations of foregut contents revealed that deep-inhabiting copepods had some intact or damaged diatoms, suggesting reutilization of rapidly sinking particles in the deeper layers. A comparison of observed particulate carbon fluxes with estimated copepod matabolic activities suggests that 38% of the falling particles in the depth range 150–1000 m are consumed by copepods.