Characterizing phytoplankton distribution and dynamics in the world's open oceans requires in situ observations over a broad range of space and time scales. In addition to temperature/salinity measurements , Biogeochemical-Argo (BGC-Argo) profiling floats are capable of autonomously observing at high-frequency bio-optical properties such as the chlorophyll fluorescence, a proxy of the chlorophyll a concentration (Chla), the particulate backscattering coefficient (b bp), a proxy of the stock of particulate organic carbon , and the light available for photosynthesis. We analyzed an unprecedented BGC-Argo database of more than 8,500 multivariable profiles collected in various oceanic conditions, from subpolar waters to subtropical gyres. Our objective is to refine previously established Chla versus b bp relationships and gain insights into the sources of vertical, seasonal, and regional variability in this relationship. Despite some regional, seasonal and vertical variations, a general covariation occurs at a global scale. We distinguish two main contrasted situations: (1) concomitant changes in Chla and b bp that correspond to actual variations in phytoplankton biomass, e.g., in subpolar regimes; (2) a decoupling between the two variables attributed to photoacclima-tion or changes in the relative abundance of nonalgal particles, e.g., in subtropical regimes. The variability in the b bp :Chla ratio in the surface layer appears to be essentially influenced by the type of particles and by photoacclimation processes. The large BGC-Argo database helps identifying the spatial and temporal scales at which this ratio is predominantly driven by one or the other of these two factors.