A Brief History of Modelling Marine Ecology in the Upper Ocean

The upper mixed layer of ocean is an important parameter which plays a vital role in understanding several phenomena occurring in the upper ocean. This layer occurs between the ocean surface and up to a depth where the physical properties like temperature, salinity and density are nearly vertical uniform. It also plays a significant role in the exchange of energy and mass between atmosphere and the underlying ocean influencing marine ecological dynamics. This article highlights the evolution of theoretical ecological modelling based on differential equations and its logical extension to attempts at formulation of quantitative descriptions which require computer simulations. In particular, emphasis is on models coupling the biological processes with the physical environmental forcing through a simple parameterization of the seasonal changes in the upper mixed layer. Finally a case study comparing the ecological dynamics in the mixed layers of the two basins in the Northern Indian Ocean, viz. the Arabian Sea (AS) and the Bay of Bengal (BoB), is presented. The basins provide a study in contrast and it is important to understand and compare the seasonal cycles of biological response to the different physical processes in the two basins. The model simulated phytoplankton results are validated with available data of Chl-a in both the basins. The model results confirm that the higher biological productivity in the AS compared to BoB is mainly due to the more dynamic physical process induced deeper MLD and increased entrainment of nutrients from below the mixed layer in AS. Comparatively, varying other parameters does not produce the same effect.