Global variability of phytoplankton carbon and non-algal particles from ocean color data based on a photoacclimation model

Phytoplankton is the most important primary producer in the ocean, owing to its pivotal role at the base of the food chain and in the ocean carbon cycle. To better estimate ocean productivity, the retrieval of accurate observations of phytoplankton carbon (Cphy) biomass from ocean color satellites is of the utmost importance. When Cphy is retrieved using the backscattering signal generated by marine particles, the signal due to non-algal particles—NAP (bbNAP) must be removed. However, algorithms currently used to retrieve bbNAP do not work globally, especially in the large mid-ocean subtropical gyres. Here, we propose a new model to derive Cphy globally, including all subtropical gyres, that accounts for the estimation of phytoplankton photoacclimation when retrieving bbNAP. The new model shows more valid retrievable bbNAP coefficients than the previously published methods and values mainly around 0.0011 m−1, consistent with coefficients estimated with in situ observations. Moreover, the retrieved Cphy concentrations show a relative error of 7% with respect to in situ measured picophytoplankton carbon data. Our research indicates that the photoacclimation status of phytoplankton must be addressed to confidently retrieve bbNAP and Cphy at the global scale from ocean color measurements.