Numerical simulations of the global ocean biogeochemistry: Theory, applications and future developments.

Marine ecosystems are tightly connected to the Earth climate and several possible feedbacks may occur in a changing system. Earth System Models
(ESM) consider marine ecosystems as an important component of the global carbon cycle that affects the concentration of atmospheric CO2. The complexity of ecosystems is such that their description is limited to the parameterization of the major planktonic components and pelagic biogeochemical processes.
Therefore, the theoretical formulation of the equations for marine pelagic biogeochemistry is generally presented as a 3-D advection-diffusion-reaction problem for conservation laws.
This talk presents an overview of the mathematical representation of the reaction terms, which includes marine trophic interactions and major biogeochemical cycles of elements (C, N, P, Si, O, Fe). The proposed formulation revisits and generalizes the stoichiometric approach of the European Regional Seas Ecosystem Model (ERSEM) by identifying basic biogeochemical constituents and defining the state variables as living functional groups and chemical functional families. Model equations are written in a comprehensive and unified form, which highlights the major pelagic biogeochemical processes involved in the functional role of producers, consumers and decomposers in the global ocean ecosystem.
The global ocean implementation is realized through an on-line coupling with an ocean general circulation model (OPA, with ORCA2 resolution) forced with atmospheric surface fields. Results from an ESM experiment with the ECHAM5 AGCM and the LIM sea-ice model are also presented. The talk will finally present the possible linkages between applied mathematics and the simulation of marine biogeochemical processes.