Temporal variability of the carbonate system and air-sea CO 2 exchanges in a Mediterranean human-impacted coastal site

International audience; The temporal evolution of the carbonate system and air-sea CO 2 fluxes are investigated for the first time in the Bay of Marseille (BoM-North Western Mediterranean Sea), a coastal system affected by anthropogenic forcing from the Marseille metropolis. This study presents a two-year time-series (between 2016 and 2018) of fortnightly measurements of A T , C T, pH and derived seawater carbonate parameters at the SOLEMIO station. On this land-ocean boundary area, no linear relationship between A T and salinity in surface water is observed due to sporadic intrusions of freshwater coming from the Rhone River. On an annual scale, the BoM acts as a sink of atmospheric CO 2. This result is consistent with previous studies in the Mediterranean Sea. Mean daily air-sea CO 2 fluxes range between −0.8 mmol C.m −2 .d −1 and-2.2 mmol C.m −2 .d −1 during the study period, depending on the atmospheric CO 2 sampling site used for the estimates. This study shows that the pCO 2 in the surface water is predominantly driven by temperature changes, even if partially counterbalanced by biological activity. Therefore, temperature is the main contributor to the air-sea CO 2 exchange variability. Mean daily Net Ecosystem Production (NEP) estimates from C T budget shows an ecosystem in which autotrophic processes are associated with a sink of CO 2. Despite some negative NEP values, the observed air-sea CO 2 fluxes in the BoM are negative, suggesting that thermodynamic processes are the predominant drivers for these fluxes.