Dissolved inorganic carbon profiles and fluxes determined using pH and PCO2 microelectrodes

Submillimeter depth distributions of total dissolved inorganic carbon (DIC) were derived from pH and P-CO2 profiles measured with microelectrodes in an organic-rich, laboratory-maintained sediment. The DIC profiles were used to calculate diffusive fluxes of DIC across the sediment-water interface. In two experiments, the calculated diffusive fluxes fell within +/-50% of the total flux of DIC determined by core incubation. An assessment of errors suggests that the microelectrode-derived estimates are not significantly different from measured total DIC fluxes (P = 0.05). It is concluded, therefore, that pH and P-CO2 microelectrode measurements can be paired to determine fine-scale pore-water DIC profiles and DIC diffusive fluxes. Problems will arise only in situations in which pH and P-CO2 gradients are extremely steep or spatially heterogeneous; this is because these conditions can cause mismatching of pH and P-CO2 measurements or CO2 system disequilibrium.