Temperature dependence and rates of sulfate reduction in cold sediments of Svalbard, Arctic Ocean

Sediments of permanently cold areas around Svalbard and northern Norway were examined for their sulfate reduction activities and the degree of adaptation of their bacterial communities toward low temperatures. Depth distributions of sulfate reduction rates were obtained from whole-core incubations with sulfur-35-labeled sulfate as tracer. The integrated rates from the sediment surface to a depth of 15 cm ranged between 0.9 and 4.1 mmol m(-2) day(-1), comparable to rates in shelf sediments of temperate climates. The temperature dependence of sulfate reduction was investigated by incubation of anoxic sediment slurries in a temperature gradient block at -5 degrees C to + 40 degrees C. Sulfate reduction rates increased 4- to 10-fold from in situ temperature to the optimum temperature, and highest measured rates reached nearly 200 nmol ml(-1) day(-1) at 27 degrees C. The optimum temperatures, 25-30 degrees C, indicated a mesophilic community of sulfate-reducing bacteria and were at least 20 degrees C higher than the in situ temperatures of -1.7 to 2.6 degrees C. Arrhenius plots were linear from the lowest temperatures nearly to the optimum temperatures, and activation energies fell in the range of 40-75 kJ mol(-1), that is, at the lower end of previously reported values. Samples from depths below 15 cm showed enhanced rates as a result of substrate addition, whereas the optimum temperatures did not change. The high rates at in situ temperatures and the low activation energies are indications of a cold-adapted population of mesophilic or moderately psychrophilic sulfate-reducing bacteria in these sediments