Carbonate Alkalinity in the Pore Waters of Anoxic Marine Sediments1

The principal factor affecting carbonate alkalinity in pore waters of organic‐rich aluminosilicate muds from the central Connecticut coast and a Maine fjord is bacterial sulfate reduction. Measured (titration) alkalinity is equal to that calculated from measured changes in SO 4 2− , Mg 2+ , Ca 2+ , and NH 4 + . As a result of alkalinity increase, pore waters of anoxic sediments can become highly supersaturated with CaCO 3 . Precipitation of Ca.CO 3 may not occur, however, possibly because of the inhibiting effect of dissolved organic matter. No evidence is provided by these sediments for authigenic aluminosilicate formation.