The link between phytoplankton primary production (PPP) and chromophoric dissolved organic matter (CDOM) has been demonstrated indirectly in the laboratory, but not directly in the sea. Here, for the first time, we report a strong link between PPP and CDOM in a study carried out in coastal marine waters around Barcelona (NW Mediterranean) in contrasting seasons. We measured relevant correlations between a CDOM concentration and both PPP (r = 0.89, p < 0.001, n = 16; r = 0.76, p < 0.01, n = 10; and r = 0.68, p < 0.001, n = 26; for summer, winter–spring and both seasons together, respectively) and the specific production rate at optimal light intensity (P ; r = 0.77, p < 0.001, n = 16; r = 0.86, p < 0.01, n = 10; and r = 0.85, p < 0.001, n = 26; for the same seasons). Based on our findings, we design a model that predicts PPP very well, using a CDOM, water temperature and photosynthetically active radiation (PAR)(R = 0.84, p < 0.001, n = 26). Relationships between CDOM concentration parameters (measured at wavelengths of 280, 300, 340, 355, 375, 412 and 460 nm) and variables associated to CDOM processes (chlorophyll-a, bacterial abundance, turbidity related to sediment resuspension and PAR) were also evaluated. Bacterial abundance is significantly correlated with CDOM concentration measured at higher wavelengths when all samples are considered (e.g., r = 0.82, p < 0.001, n = 26, for a CDOM). However, in seasonal data analysis, the correlations decrease slightly (summer season: e.g., r = 0.79, p < 0.001, n = 16, for a CDOM) or become non-significant (winter–spring season: e.g., r = -0.02, p = 0.95, n = 10, for a CDOM). Sunlight photobleaching and sediment resuspension processes significantly influence CDOM dynamics in the summer (for a CDOM: r = -0.72, p < 0.001, n = 16; and r = 0.67, p < 0.01, n = 16, respectively)

This work was supported by the Catalan Water Agency (Departament de Medi Ambient i Habitatge, Generalitat de Catalunya) through its Monitoring and Control Program (PSIC) of Catalan coastal waters

11 pages, 6 figures, 2 tables, supplementary material https://doi.org/10.1016/j.pocean.2019.05.008

Peer Reviewed