An initial carbon export assessment in the Mediterranean Sea based on drifting sediment traps and the Underwater Vision Profiler data sets,
Résumé
During the SESAME EU FP6 project, all available particulate organic carbon (POC) data collected from drifting
sediment trap and Underwater Vision Profiler deployments (INSU PROOF database, 1991–2011) were
gathered in order to assess carbon export at the scale of the Mediterranean Sea. In this study, we observed
that particle size, POC export, and the contribution of microphytoplankton to the phytoplankton community
structure, all decreased following the west to east net primary production gradient. One the other hand, no clear
longitudinal gradient was found regarding particle composition (C/N ratio or lipid content). The above
longitudinal patterns were also observed at the seasonal scale from spring to summer in the northwestern subbasin.
These observations suggest that particle size rather than organic matter composition controls fluxes of
POC in the Mediterranean Sea. The comparison between POC and dissolved organic carbon (DOC) fluxes
highlights the different time-scale of physicals vertical mechanisms and suggests that DOC flux can play an
underestimated role in the supply of fresh carbon to the deep waters Mediterranean Sea. Indeed, DOC supply to
deeper layers can be one order of magnitude larger than particle carbon flux but occurs in pulses when
stratification breaks due to (i) deep-water formation, or (ii) winter mixing. In contrast, the vertical export of
POC occurs throughout the year bringing weak, but almost continuous, energy to meso- and bathypelagic
organisms.