Acidification of Lower St. Lawrence Estuary Bottom Waters |
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| Authors: | Alfonso Mucci Michel Starr Denis Gilbert Bjorn Sundby |
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| Institution: | 1. Department of Earth and Planetary Sciences , McGill University , 3450 University Street, Montréal, Quebec, H3A 2A7alfonso.mucci@mcgill.ca;3. Maurice Lamontagne Institute , Fisheries and Oceans Canada, P.O. Box 1000, Mont-Joli, Quebec, G5H 3Z4;4. Department of Earth and Planetary Sciences , McGill University , 3450 University Street, Montréal, Quebec, H3A 2A7;5. Institut des Sciences de la Mer de Rimouski , 310 Allée des Ursulines, Rimouski, Quebec, G5L 3A1 |
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| Abstract: | Accumulation of metabolic CO2 can acidify marine waters above and beyond the ongoing acidification of the ocean by anthropogenic CO2. The impact of respiration on carbonate chemistry and pH is most acute in hypoxic and anoxic basins, where metabolic CO2 accumulates to high concentrations. The bottom waters of the Lower St. Lawrence Estuary (LSLE), where persistently severe hypoxia has developed over the last 80 years, is one such case. We have reconstructed the evolution of pH in the bottom waters from historical and recent data, and from first principles relating the stoichiometry of CO2 produced to oxygen consumed during microbial degradation of organic matter. Based on the value of the atmospheric partial pressure of CO2 that best reproduces the preformed dissolved inorganic carbon concentration in the bottom waters, we estimate the average ventilation age of the bottom waters to be 16?±?3 years. The pH of the bottom waters has decreased by 0.2 to 0.3 over the last 75 years, which is four to six times greater than can be attributed to the uptake of anthropogenic CO2. The pH decrease is accompanied by a decline in the saturation state with respect to both calcite and aragonite. As of 2007, bottom waters in the LSLE are slightly supersaturated with respect to calcite (Ωc?≈?1.06?±?0.04) but are strongly undersaturated with respect to aragonite (Ωa?≈?0.67?±?0.03). |
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| Keywords: | acidification oxygen depletion metabolic CO2 St Lawrence Estuary |
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