Zooplankton field heterogeneity formation on the mesoscale: elements of the theory and empirical characteristics

The continuous records of mesozooplankton biomass (with the spatial averaging of pump track every 20 km) were carried out from the surface layer (2–6 m depth) over 5 transects in the western part of the Indian Ocean during the end of the north-east monsoon period. The spatial autocorrelation functions have shown that the average size of zooplankton heterogeneities on the mesoscale is close to 40 km. To model the field of zooplankton biomass b(t, x) the model based on the equation of non-conservative substance diffusion was applied: dbbt + u(dbdx) = k(d2bdx2) + nb + a(t, x), where t is the time; x the horizontal coordinate; u the velocity of mass transport by a current; k the coefficient of horizontal turbulent diffusion and n the normalised velocity of zooplankton growth. The field a(t, x) characterises the rest of the local fluctuations of zooplankton biomass not associated with the mentioned processes. The techniques of solving the equation based on the spectral theory of the random fields was solved by means of the evaluation of the field autocovariation functions.