Isotopic analysis of sulfate in a South Pacific core

The sulfur-34 isotope profile of sulfate in a red-clay sediment gravity core, 120 cm long, from the South Pacific indicates a very weak, if any, bacterial sulfate-reducing activity. This activity is not shown by the oxygen-18 distribution. The sulfur and oxygen isotopic values are close to those of the overlying seawater sulfate and to the average oceanic values.Of all the parameters mainly able to affect the bacterial activity, such as temperature, molecular oxygen and organic matter, the very small concentration of organic matter seems to be responsible for the almost total lack of sulfate reduction.