ABSTRACT

Vertical profiles of turbulent kinetic energy dissipation rate (e), current velocity, temperature, salinity, chlorophyll fluorescence, and copepods were sampled for four days at an anchor station on the southern flank of Georges Bank when the water column was stratified in early June, 1995. Copepodite stages of Temora spp., Pseudocalanus spp., Oithona spp. and Calanus finmarchicus, and all of their naupliar stages except for Temora spp., were found deeper in the water column when turbulent dissipation rates in the surface mixed layer increased in response to increasing wind stress. Those taxa that initially occurred in the surface mixed layer at 10-15 m depth (e #10-8 W/kg) before the wind were located in the pycnocline at 20-25 m depth when dissipation rates at 10 m increased up to 10-6 W/kg. Dissipation rates in the pycnocline were similar to those experienced at shallower depths before the wind. After passage of the wind event and with relaxation of dissipation rates in the surface layer, all stages returned to prior depths. Temora spp. nauplii did not migrate. Our results indicate that turbulence from a moderate wind event can influence the vertical distribution of copepods in the surface mixed layer. Changes in the vertical distribution of copepods can impact trophic interactions, and movements related to turbulence would affect the application of turbulence theory to encounter and feeding rates.

Keywords: Turbulence, zooplankton, vertical distribution, vertical migration, chlorophyll maximum, stratification, mixing