Temperature characteristics of bacterial sulfate reduction in continental shelf and slope sediments

The temperature responses of sulfate-reducing mi- crobial communities were used as community temperature characteristics for their in situ temperature adaptation, their origin, and dispersal in the deep sea. Sediments were col- lected from a suite of coastal, continental shelf, and slope sediments from the southwest and southeast Atlantic and per- manently cold Arctic fjords from water depths ranging from the intertidal zone to 4327 m. In situ temperatures ranged from 8 C on the shelf to 1 C in the Arctic. Tempera- ture characteristics of the active sulfate-reducing community were determined in short-term incubations with 35 S-sulfate in a temperature gradient block spanning a temperature range from 0 to 40 C. An optimum temperature (Topt) between 27 C and 30 C for the South Atlantic shelf sediments and for the intertidal flat sediment from Svalbard was indicative of a psychrotolerant/mesophilic sulfate-reducing community, whereasTopt 20 C in South Atlantic slope and Arctic shelf sediments suggested a predominantly psychrophilic commu- nity. High sulfate reduction rates (20-50 %) at in situ temper- atures compared to those at Topt further support this interpre- tation and point to the importance of the ambient temperature regime for regulating the short-term temperature response of sulfate-reducing communities. A number of cold (< 4 C) continental slope sediments showed broad temperature op- tima reaching as high as 30 C, suggesting the additional presence of apparently mesophilic sulfate-reducing bacte- ria. Since the temperature characteristics of these mesophiles do not fit with the permanently cold deep-sea environment, we suggest that these mesophilic microorganisms are of al- lochthonous origin and transported to this site. It is likely that they were deposited along with the mass-flow move- ment of warmer shelf-derived sediment. These data therefore suggest that temperature response profiles of bacterial carbon mineralization processes can be used as community tempera- ture characteristics, and that mixing of bacterial communities originating from diverse locations carrying different temper- ature characteristics needs to be taken into account to explain temperature response profiles of bacterial carbon mineraliza- tion processes in sediments.