Abstract
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, resulting in a potential major role of dissolved organic carbon (DOC) export in the biological pump. Strong DOC accumulation in surface waters is already well documented, though measurements of DOC stocks and export flux are still sparse and associated with major uncertainties. This study provides the first basin-scale overview and analysis of organic carbon stocks and export fluxes in the Mediterranean Sea through a modeling approach based on a coupled model combining a mechanistic biogeochemical model (Eco3M-MED) and a high-resolution (eddy-resolving) hydrodynamic simulation (NEMO-MED12). The model is shown to reproduce the main spatial and seasonal biogeochemical characteristics of the Mediterranean Sea. Model estimations of carbon export are also of the same order of magnitude as estimations from in situ observations, and their respective spatial patterns are mutually consistent. Strong differences between the western and eastern basins are evidenced by the model for organic carbon export. Though less oligotrophic than the eastern basin, the western basin only supports 39 % of organic carbon (particulate and dissolved) export. Another major result is that except for the Alboran Sea, the DOC contribution to organic carbon export is higher than that of particulate organic carbon (POC) throughout the Mediterranean Sea, 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 in light of intracellular quotas. Finally, according to the model, strong phosphate limitation of both bacteria and phytoplankton growth is one of the main drivers of DOC accumulation and therefore of export.
Highlights
The biological pump is recognized as a major component of carbon export in the ocean and plays a significant role in the carbon cycle as a whole (Siegenthaler and Sarmiento, 1993)
MDOC refers to the modeled dissolved organic carbon integrated over the first 100 m of the water column
Very high mDOC values can be found throughout in the north Adriatic Sea and along the Libyan coast. Apart from these regions, mDOC is low everywhere in winter (Fig. 3a), and this is true in spring except in the region of the spring bloom in the Provencal sub-basin
Summary
The biological pump is recognized as a major component of carbon export in the ocean and plays a significant role in the carbon cycle as a whole (Siegenthaler and Sarmiento, 1993). The sinking of organic particles has long been identified as the main process involved in the biological pump, thereby sustaining the vertical carbon and nutrient gradients in the ocean (Eppley and Peterson, 1979; Sarmiento and Gruber, 2006). Considerable attention has been paid to the export of organic carbon in its particulate form. A. Guyennon et al.: New insights into the organic carbon export in the Mediterranean Sea
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