Towards the comprehension of the inter-annual physiological response of phytoplankton to global warming as seen from space: a refined phytoplankton biomass proxy

Recent research showed that ocean warming causes an expansion of the low-chlorophyll and low-productivity areas, such as the gyres (Martinez et al., 2009; Behrenfeld et al., 2015). Satellite observations revealed an inverse relationship between inter-annual and inter-decadal changes in Sea Surface Temperature (SST) and surface phytoplankton concentration, in terms of chlorophyll (Chl) (Behrenfeld et al., 2015). However, standard Chl estimations are affected by unaccounted physiological phytoplankton processes, whose study has great relevance. Specifically, a deeper study on the inter-annual physiological response of phytoplankton to global warming is one of the main future challenges for the comprehension of how and where the oceans are going towards. To this aim, it is crucial to improve phytoplankton biomass estimations from space. Indeed, the most common index to describe and study phytoplankton physiology is through the well-known Chl to carbon ratio. This contribution presents a refined backscattering-based carbon proxy, named C_phyto, that takes into account both phytoplankton community variations (Brewin et al., 2012) and the spatio-temporal variations of the optical backscattering by non-algal particles (Bellacicco et al., 2019). Inclusion of both these issues in the C_phyto model may help to improve phytoplankton biomass detection from remote sensing data (Martinez-Vicente et al., 2017) and can be thus potentially impactful in the global biogeochemical cycles studies (e.g. primary production, carbon uptake and sink).