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Zusammenfassung:
Mineralization of organic matter and the subsequent dissolution of calcite were simulated for surface sediments of the upper continental slope off Gabon by using microsensors to measure O- 2, pH, pCO(2) and Ca2+ (in situ), pore-water concentration profiles of NO3-, NH4+, Fe2+, and Mn2+ and SO42- (ex situ), as well as sulfate reduction rates derived from incubation experiments. The transport and reaction model CoTReM was used to simulate the degradation of organic matter by O-2, NO3-, Fe(OH)(3) and SO42-, reoxidation reactions involving Fe2+ and Mn2+, and precipitation of FeS. Model application revealed an overall rate of organic matter mineralization amounting to 50 mumol C cm(-2) yr(-1), of which 77% were due to O-2, 17% to NO3- and 3% to Fe(OH)(3) and 3% to SO42-. The best fit for the pH profile was achieved by adapting three different dissolution rate constants of calcite ranging between 0.01 and 0.5% d(-1) and accounting for different calcite phases in the sediment. A reaction order of 4.5 was assumed in the kinetic rate law. A CaCO3 flux to the sediment was estimated to occur at a rate of 42 g m(-2) yr(-1) in the area of equatorial upwelling. The model predicts a redissolution flux of calcite amounting to 36 g m(-2) yr(-1), thus indicating that similar to90% of the calcite flux to the sediment is redissolved. Copyright (C) 2002 Elsevier Science Ltd.
