Dissolved trace metal concentration, sulfate, carbonate and calcium were determined in the interstitial water expressed from two marine cores taken in the borderland off Southern California. C 13/C 12 ratios were measured for both the total dissolved carbonate species, and for the solid carbonate in the sediment. One core consisted of oxidizing sediment from the San Pedro Basin (SP), the other came from the Santa Catalina Basin (SC) where reducing sediments are overlain by about two meters of oxidizing sediment. Total dissolved carbon dioxide increased in both cores, reaching a maximum of 34·4 mM in SP and 12·3 mM in SC. δC 13 of the dissolved carbonate decreased from - 1·0%. at the surface of SP to-21·2%. at 500 cm depth; in SC the decrease was from - 6·0%. at the surface to -19·3%. at 500 cm. In the SP core dissolved calcium decreased from 10·4 mM at the surface to 3·7 mM at 500 cm depth, while sulfate decreased from 6 mM to 0·1 mM. There was no marked decrease in calcium or sulfate with depth in Santa Catalina. The results indicate that the increase in dissolved carbonate with depth arises largely from metabolic activity, rather than solution of solid carbonates. Calculations based on three different approaches indicate that surface interstitial water is undersaturated in calcium carbonate compared to surface sea water, but below 2 or 3 m, the interstitial water becomes supersaturated. It is suggested that solution of calcium carbonate under low pH, below the sediment-water interface, may result in transport of calcium from the sediment column into overlying sea water.