Chlorophyll signatures and nutrient cycles in the Mediterranean Sea: a model sensitivity study to nitrogen and phosphorus atmospheric inputs

Abstract

Abstract. In this work, the relative importance of nitrogen and phosphorus, considered as external loads, on Mediterranean biogeochemical cycles is evaluated. Biomass concentrations are analysed considering the steady state response of the three-dimensional ECHYM model to three nitrogen and phosphorus atmospheric depositions, considered as continuous in time. After reaching stationary evolutions, chlorophyll surficial maps and vertical transects are compared with existing datasets, showing a good agreement at their large scale sampling. The distributions of nutrients within the biochemical compartments are analysed, highlighting, inside the Mediterranean oligotrophic environment, the role played by ultraplankton, the smaller phytoplankton compartment. For all the three different atmospheric loads, western primary production estimation is about twice than that in the eastern basin, while western secondary production is about three times the eastern one. This numerical exercise suggests that the Eastern Mediterranean, cycling at low nutrient sill, is eventually pushed toward an higher nutrient depletion, when loading new nitrogen and phosphorus.