A model for the distribution of particle flux in the mid-water column controlled by subsurface biotic interactions

The sub-euphotic zone water column is important in controlling the downward transport of material falling from the surface waters. Descriptions of the carbon flux as a function of depth have focused on empirical relationships that neglect biological processes that might control them. We develop here a series of simple models of the region that describe changes in flux in terms of the population dynamics of a particle feeder and its predator. One model predicts that the flux and predator concentration at steady state decrease exponentially with depth while the concentration of the particle feeders is constant; a second predicts that flux, particle feeder, and predator concentrations are proportional and decrease at rates that are approximately inversely proportional to depth. Away from steady state, variations in particle flux leaving the surface can induce oscillations in the near-surface animal populations but not the deeper populations. As a result of the animal oscillations associated with the surface flux variations, there can be large swings in the deep vertical particle flux that are not synchronized to the surface variations for one model formulation; a second formulation predicts that fluctuations in surface flux are damped out near the bottom. The differences in predictions for the various models make it possible to verify the utility of one or the other formulation.