Biological production in two contrasted regions of the Mediterranean Sea during the oligotrophic period: an estimate based on the diel cycle of optical properties measured by BioGeoChemical-Argo profiling floats

[摘要] This study assesses marine community production based on the dielvariability of bio-optical properties monitored by two BioGeoChemical-Argo(BGC-Argo) floats. Experiments were conducted in two distinct Mediterraneansystems, the northwestern Ligurian Sea and the central Ionian Sea, duringsummer months. We derived particulate organic carbon (POC) stock and grosscommunity production integrated within the surface, euphotic and subsurfacechlorophyll maximum (SCM) layers, using an existing approach applied to dielcycle measurements of the particulate beam attenuation ( c p ) andbackscattering ( b bp ) coefficients. The diel cycle of c p provided arobust proxy for quantifying biological production in both systems; that of b bp was comparatively less robust. Derived primary production estimatesvary by a factor of 2 depending upon the choice of the bio-opticalrelationship that converts the measured optical coefficient to POC, which isthus a critical step to constrain. Our results indicate a substantialcontribution to the water column production of the SCM layer (16 %–42 %),which varies largely with the considered system. In the Ligurian Sea, the SCMis a seasonal feature that behaves as a subsurface biomass maximum (SBM)with the ability to respond to episodic abiotic forcing by increasingproduction. In contrast, in the Ionian Sea, the SCM is permanent, primarilyinduced by phytoplankton photoacclimation, and contributes moderately towater column production. These results clearly demonstrate the strongpotential for transmissometers deployed on BGC-Argo profiling floats toquantify non-intrusively in situ biological production of organic carbon in thewater column of stratified oligotrophic systems with recurring or permanentSCMs, which are widespread features in the global ocean.

[学科分类] 大气科学