EN
The influence of episode of density-independent mortality on the time-space variability of phytoplankton distribution in the near surface layer of a stratified sea is the aim of this paper. The mortality of phytoplankton in unpredictable conditions, like a spill of crude oil or other chemicals is considered. The numerical simulations were carried out using a biological model of upper layer with a developed primary production and regeneration mechanisms and of daily migration of zooplankton. In such cases an increase in the mortality rate intensifies the decrease in phytoplankton biomass. Such a situation can on occasion lead to phytoplankton extinction, and hence to irreversible changes in its distribution area.