Thirty-five samples of deep sea sediments were collected on DSDP Leg 15 and stored in sealed kettles for over a year. The PCO2 of these kettles was monitored as a function of time and temperature. When CO2 is removed for analysis, the decrease observed in kettle PCO2 is consistent with the assumption that equilibration of water and calcite controls the alkalinity and pH of the interstitial water. An empirical relation between ΣCC>2 and PCO2 is selected which allows correction for CO2 removal and comparison of PCO2 to other carbonate parameters (i.e., pH) measured on Leg 15. The resolution of the data is limited, but pH and PCO2 appear to be consistent within 0.1 pH units. Calculation of the degree of calcite saturation is used to suggest that pressure may significantly influence ionic equilibria between clay and pore waters, causing samples from Site 149 to appear understaurated with calcite. Sediment samples from regions with strong [SC 4 = ] gradients show increases in PCO2 with time, indicating active sulfate reduction continuing in the kettles. Comparison of the CO2 generation rate in the laboratory with that in situ at Sites 147 and 148 suggests that the process may be limited by the availability of suitable organic substrates, which is a function of temperature.

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