New insights into the organic carbon export in the Mediterranean Sea from 3-D modeling

Abstract. The Mediterranean Sea is one of the most oligotrophic regions of the oceans, and nutrients have been shown to limit both phytoplankton and bacterial activities. This has direct implications on the stock of dissolved organic carbon (DOC), whose high variability has already been well-documented even if measurements are still sparse and are associated with important uncertainties. We here propose a Mediterranean Basin-scale view of the export of organic carbon, under its dissolved and particulate forms. For this purpose, we have used a coupled model combining a mechanistic biogeochemical model (Eco3M-MED) and a high-resolution (eddy-resolving) hydrodynamic simulation (NEMO-MED12). This is the first Basin-scale application of the biogeochemical model Eco3M-MED and is shown to reproduce the main spatial and seasonal biogeochemical characteristics of the Mediterranean Sea. Model estimations of carbon export are of the same order of magnitude as estimations from in situ observations, and their respective spatial patterns are consistent with each other. As for surface chlorophyll, nutrient concentrations, and productivity, strong differences between the Western and Eastern Basins are evidenced by the model for organic carbon export, with only 39% of organic carbon (particulate and dissolved) export taking place in the Western Basin. The major result is that except for the Alboran Sea, dissolved organic carbon (DOC) contribution to organic carbon export is higher than that of particulate (POC) in the whole Basin, especially in the Eastern Basin. This paper also investigates the seasonality of DOC and POC exports as well as the differences in the processes involved in DOC and POC exports.