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

[摘要] The Mediterranean Sea is one of the most oligotrophic regions of the oceans,and nutrients have been shown to limit both phytoplankton and bacterialactivities, resulting in a potential major role of dissolved organic carbon(DOC) export in the biological pump. StrongDOC accumulation in surface watersis already well documented,though measurements of DOC stocks and export flux are still sparse andassociated with major uncertainties. This study provides the firstbasin-scale overview and analysis of organic carbon stocks and export fluxesin the Mediterranean Sea through a modeling approach based on a coupledmodel combining a mechanistic biogeochemical model (Eco3M-MED) and ahigh-resolution (eddy-resolving) hydrodynamic simulation (NEMO-MED12). Themodel is shown to reproduce the main spatial and seasonal biogeochemicalcharacteristics of the Mediterranean Sea. Model estimations of carbon exportare also of the same order of magnitude as estimations from in situobservations, and their respective spatial patterns are mutuallyconsistent. Strong differences between the western and eastern basins areevidenced by the model for organic carbon export. Though less oligotrophicthan 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 DOCcontribution to organic carbon export is higher than that of particulateorganic carbon (POC) throughout the Mediterranean Sea, especially in the eastern basin.This paper also investigates the seasonality of DOC and POC exports as wellas the differences in the processes involved in DOC and POC exports inlight of intracellular quotas. Finally, according to the model, strongphosphate limitation of both bacteria and phytoplankton growth is one of the main drivers of DOC accumulation and therefore of export.

[学科分类] 地球化学与岩石