Biological heating effect of a band of phytoplankton

Abstract

The presence of phytoplankton in a body of water affects the penetration of irradiance through the water column. This influences the temperature and hence the density distribution of the water. If the phytoplankton concentration varies horizontally, then the consequent density distribution will result in a horizontal pressure gradient. Here we consider a long band (or strip) of high phytoplankton biomass, flanked on either side by clearer water containing little biomass. By means of a simple model, we present calculations of the velocities induced by the pressure gradients to show under what conditions the differential heating effects may become significant. The model's momentum equations assume a steady state, and include effects of Coriolis and vertical eddy viscosity. An analytical solution is obtained, and the induced velocities are shown graphically. Further calculations investigate the potential for the biologically induced vertical velocities to transport nutrients into the surface waters and subsequently influence new primary production. This work demonstrates the capacity for feedbacks from the biological component of the ecosystem to the physical component (and back again).