A massive dissolved inorganic carbon release at spring tide in a highly turbid estuary -: art. no. L09316

In September 2003, the highly turbid Loire estuary ( France) showed drastic oxygen depletions (down to 11% of saturation), high pCO(2) (up to 3740 muatm) 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 mumol. kg(-1) for DIC, by 80 +/- 14 mueq.kg(-1) for Total Alkalinity (TA) and by 684 +/- 142 muatm for pCO(2). In parallel, oxygen decreased by 65 +/- 12 mumol. 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.