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

[1] In September 2003, the highly turbid Loire estuary (France) showed drastic oxygen depletions (down to 11% of saturation), high pCO 2 (up to 3740 matm) and high CO 2 fluxes (280 ± 100 mmol.m A2 .d A1). 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 mmol.kg A1 for DIC, by 80 ± 14 meq.kg A1 for Total Alkalinity (TA) and by 684 ± 142 matm for pCO 2. In parallel, oxygen decreased by 65 ± 12 mmol.kg A1. 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 CO 2 flux from the estuary, but to 60% to the net TA production in the estuary.