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

Abstract

AbstractWe 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 (bbp(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 bbp(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 bbp(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.