Particulate concentration and seasonal dynamics in the mesopelagic ocean based on the backscattering coefficient measured with Biogeochemical-Argo floats

International audienceWe explore a novel and spatially extensive data set obtained from Biogeochemical-Argo (or BGC-Argo) floats, containing 16,796 profiles of the particulate backscattering coefficient at 700 nm (b bp (700)) measured with three different sensors. We focus at the 900-950m depth interval (within the mesopelagic), where we found values to be relatively constant. While we find significant differences between estimates of b bp (700) obtained with different sensors (≈30% disagreement), the median values in most oceanic regions obtained with a single type of sensor are within 50% of each other and are consistent with measurements of suspended mass conducted in the early 1970s. Deviations from the quasi-constant background value likely indicate times and locations associated with higher particulate export to depth. Indeed, we observe that in productive high-latitude regions, a deep seasonal signal is observed, with enhanced values recorded a few months after surface spring/summer maximal concentrations. In addition, the deep b bp (700) is highest in regions exhibiting suboxic-anoxic conditions (e.g., Northern Indian Ocean), which have been associated with local particulate production as well as reduced particle flux attenuation