Global Variability of Optical Backscattering by Non-algal particles From a Biogeochemical-Argo Data Set

Understanding spatial and temporal dynamics of non-algal particles in open ocean is of the utmost importance to improve estimations of carbon export and sequestration. These particles covary with phytoplankton abundance but also accumulate independently of algal dynamics. The latter likely represents an important fraction of organic carbon, but it is largely overlooked. A possible way to study these particles is via their optical backscattering properties (b(bp)) and relationship with chlorophyll-a (Chi). To this aim, we estimate the fraction of b(bp) associated with the non-algal particle portion (b(bp)(k)) that does not covary with Chl by using a global Biogeochemical-Argo data set. We quantify the spatial, temporal, and vertical variability of b(bp)(k). In the northern productive areas, b(bp)(k) is a small fraction of b(bp) and shows a clear seasonal cycle. In the Southern Ocean, b(bp)(k) is a major fraction of total b(bp). In oligotrophic areas, b(bp)(k) has a smooth annual cycle.