A massive dissolved inorganic carbon release at spring tide in a highly turbid estuary

In September 2003, the highly turbid Loire estuary (France) showed drastic oxygen depletions (down to 11% of saturation), high pCO2 (up to 3740 μatm) and high CO2 fluxes (280 ± 100 mmol.m−2.d−1). A rapid rise in Dissolved Inorganic Carbon (DIC) was observed when the tidal amplitude increased from 3.8 m to 5.8 m. In two days, average concentrations in the 0.1–25 salinity range increased by 106 ± 17 μmol.kg−1 for DIC, by 80 ± 14 μeq.kg−1 for Total Alkalinity (TA) and by 684 ± 142 μatm for pCO2. In parallel, oxygen decreased by 65 ± 12 μmol.kg−1. These changes in concentrations were attributed in majority to a massive fluid mud resuspension in the estuarine turbidity maximum. At spring tide, this DIC input was 30% higher than the river input. When averaged over the neap‐spring period, resuspension contributed to only 10% of the atmospheric CO2 flux from the estuary, but to 60% to the net TA production in the estuary.