CaCO3 dissolution in California continental margin sediments: The influence of organic matter remineralization

In situ benthic flux chamber and oxygen microelectrode and shipboard porewater results have been used to quantify sea floor dissolution of CaCO3 on the continental rise adjacent to central California, USA. The porewater distributions and benthic fluxes of O-2, NO3-, TA, Ca2+, delta(13)C, and TIC are interpreted using a numerical simulation of organic matter remineralization and CaCO3 dissolution in marine sediments. The processes considered in the simulation include: organic matter oxidation by mixing and sediment accumulation. Calculated benthic fluxes of O-2, NO3-, TA, TIC, delta(13)C, and Ca2+; porewater concentrations of O-2, NO3-, and NH4+; and sediment distributions of organic carbon, CaCO3, excess Pb-210, and C-14 agree well with the measurements. Benthic fluxes of alkalinity and inferred CaCO3 dissolution rates cannot be explained on the basis of dissolution driven solely by bottom water undersaturation. If the influence of metabolically-produced CO2 is included, benthic fluxes are fully reconciled, however. This is in agreement with benthic chamber Ca2+ and delta(13)C results that independently imply substantial CaCO3 dissolution in these sediments. The above observations are in contrast to those reported by Jahnke et al. (1994) for the west African continental rise and the western equatorial Pacific where l-G diagenetic models predict dissolution fluxes larger than observed with benthic flux chambers. We conclude that the extent of metabolic CaCO3 dissolution may vary regionally. Numerous factors, such as the depth of metabolic CO2 production and CaCO3 dissolution kinetics, are known or predicted to influence metabolic dissolution, Among the factors that should be considered in reconciling these observations are: (1) the extent to which sulfate reduction and reoxidation reactions may influence acid-base properties in surface sediments and (2) the total sedimentary CaCO3 content of the sites that may influence porewater acidity through surface exchange reactions at the mineral surface. Copyright (C) 1997 Elsevier Science Ltd.