Adaptive nitrogen to phosphate ratio in biogeochemical models, consequences for the stoichiometry of the Mediterranean Sea

Biogeochemical marine models aim to replicate the chemical and low-trophic levels conditions of marine ecosystems. There are many types of such models, depending on complexity, specific aims and formulations. All of them are but rough approximation of the real ecosystems with many shortcomings and drawbacks so improvements and new formulations are always needed in order to increase their capability to reproduce real-life conditions. Here we present a modification of the biogeochemical model developed at JRC for representing marine conditions in the Mediterranean Sea, the MedERGOM model. This model has been demonstrated to properly represent biological production patterns in the basin but had some difficulties in simulating correctly concentrations of free nutrients in the seawater. In the present report we modify the internal ratio of the two main nutrients in the sea (nitrate and phosphate) by taking into account the physiological flexibility plankton communities show in the real environment. By making this simple modification we show how nutrients levels in seawater simulated by MedERGOM become much closer to observations, enhancing the capability of the marine modelling framework to simulate chemical conditions in nutrient-starved basins such as the Mediterranean Sea.