Determination of phytoplankton groups from ocean color spectral measurements in the Senegalo-Mauritanian upwelling

International audienceOcean color measurements have been intensively used to estimate chlorophyll-a concentration (Chl-a in abreviation) in the surface waters of the ocean, marginal seas and lakes.Phytoplankton is the first element in the ocean food webs and consequently drives the ocean productivity. It also plays a fundamental role in climate regulation by trapping atmospheric CO2 through gas exchanges at the sea surface. With the growing interest in climate change, one may ask how the different phytoplankton populations will respond to changes in ocean characteristics (temperature, salinity) and nutrient supply.Pigment analysis by High Performance Liquid Chormatography (HPLC) has been widely used to categorized broad Phytoplancton size classes (PSC) or phytoplancton functional types (PFT) [Hirata et al. 2011]. Each phytoplancton group (PSC/PFT) is associated with diagnostic pigments and a convertion formula can be derived to estimate the percentage of each group from the pigment measurements.These in-situ measurements were used to build relationships between PSC/PFT and ocean properties that can be derived from satellite ocean color sensors (e.g. Chl-a concentration or water leaving-radiance), which is of fundamental interest to understand the phytoplankton behavior and to model its evolution [Uitz et al., 2006, Ciotti and Bricaud, 2006, Hirata et al., 2008, Sathyendranath et al., 2014, Alvain et al., 2005, Alvain et al., 2012].In the present work, we propose a regional algorithm based on PHYSAT [Alvain et al., 2012], that estimates diagnostic pigments associated with PFT/PSC from satellite ocean color measurements. The region of application is the senegalo-mauritean upwelling and the results focused on the relative concentration of Fucoxanthin (Fuco) which is the main diagnostic pigment for Microplankton (>20µm) and Diatoms