DOM-Bacteria interactions in marine systems: A modelling study.

We propose a theoretical model describing the interactions between dissolved organic carbon (DOC) and bacteria and the mechanisms leading to DOC accumulation. The model assumes that DOC cycling time-scales may vary depending on the chemical characteristics of the dissolved organic matter (DOM) and describes the temporal variability of the bacterial growth efficiency (BGE) in response to changing availability of nutrients, semi-labile and semi-refractory DOC. The conceptual framework is tested in a zero-dimensional numerical model in 2 different contexts: a diatom–bacteria system, and a microbial loop system (with bacteria, pico-phytoplankton and heterotrophic nano-flagellates). Sensitivity analyses were performed on both systems by varying the initial conditions of nutrients. Model simulations highlight the link between DOC accumulation and nutrient availability and reproduce some of the observed bacterial and microbial loop features such as the competition between bacteria and phytoplankton for nutrients and the BGE decrease in the transition from eutrophic to oligotrophic conditions. In the microbial loop simulations the model reaches a steady state and the system sustains itself without invoking external sources of N and P.