Primary and bacterial production in the Mediterranean Sea: a modelling study

Relationships between bacterial and primary production in the eastern and western basins of the Mediterranean Sea are different. In this study, a ID coupled ecosystem model is used to simulate primary and bacterial production along the west-east trophic gradient and to ascertain the physical and biogeochemical controls that determine regional variations in production. Simulations demonstrate differences in ecosystem function between the western and eastern basins of the Mediterranean Sea at the level of bacterial and primary production. Vertical mixing processes (deep mixing and convection), particularly in late winter, are crucial in determining total annual production in both basins, and the dissolved organic carbon pool, from which bacteria obtain their carbon, is derived from autotrophic rather than heterotrophic activity. Bacterial production is nutrient limited in the cast, and may be grazer controlled in the west. The dissolved organic nutrient pools are derived from heterotrophic rather than autotrophic activity. The eastern basin is characterised by strong competition between phytoplankton and bacteria for nutrients whereas the western basin is characterised by relatively high levels of heterotrophic activity. Nitrogen and phosphate uptake by phytoplankton is biologically important in both basins, whereas bacterial uptake of these is only important in the eastern basin. A generic model parameterisation produces simulation results which concur with recent observations although simulated production rates are very sensitive to the initial conditions upon which those simulations are based. (C) 2002 Elsevier Science B.V. All rights reserved.