SS3.02 Turbulence and Plankton Dynamics
Date: Wednesday, June 12, 2002
Time: 2:15:00 PM
Location: Saanich
 
RossON, Southampton Oceanography Centre, Southampton, United Kingdom, o.ross@soton.ac.uk
Sharples, J, , Southampton Oceanography Centre, Southampton, United Kingdom, js1@soc.soton.ac.uk
 
ALGAL MOTILITY IN VARIABLE TURBULENCE
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Motile phytoplankton species are suspected to use their motility for adjusting their vertical position in the water column in order to optimise the availability of both light and nutrients as their primary resources for growth. However, the turbulent velocity scales in coastal regimes are usually greater than the swimming speeds for most motile algae. In addition, the size of the smallest turbulent eddies is larger than the limited motility range of a cell and hence the algae swim in a randomly spinning viscous bubble. The general question that we try to address is thus: why are some phytoplankton motile if their swimming speeds are generally inferior to the turbulent velocity scales in coastal waters and to what extent are they able to use their motility as a competitive advantage in various turbulent regimes? The problem is addressed through a coupled 1D physical-biological Lagrangian model with realistic external forcing. As a first case study we examine the situation in the partially mixed estuary of Southampton Water where the tides produce periods of strong vertical mixing and an extended period of low turbulence during which experimental data shows accumulations of the phytoplankters near the surface. The model results indicate how the amount of turbulent mixing, coupled with the timing of the tidal cycle relative to the diel irradiance cycle and the speed at which a cell can swim, affects the dynamics of and light availability to an individual cell.