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Abstract:
The temperature dependence of representative initial and terminal steps of organic carbon remineralization was measured at 2 temperate sites with annual temperature ranges of 0 to 30 degrees C and 4 to 15 degrees C and 2 Arctic sites with temperatures of 2.6 and -1.7 degrees C. Slurried sediments were incubated in a temperature gradient block spanning a temperature range of ca 45 degrees C. The initial step of organic carbon remineralization, macromolecule hydrolysis, was measured via the enzymatic hydrolysis of fluorescently labeled polysaccharides. The terminal steps of organic carbon remineralization were monitored through consumption of oxygen and reduction of (SO42-)-S-35. At each of the 4 sites, the temperature response of the initial step of organic carbon remineralization was similar to that of the terminal steps. Although optimum temperatures were always well above ambient environmental temperatures, optimum temperatures generally decreased with decreasing environmental temperatures. Activity at 5 degrees C as a percentage of highest activity was highest in the Arctic sites and lowest in the warmest temperate site. The highest potential rates of substrate hydrolysis were measured in the Arctic, while the highest rates of oxygen consumption and sulfate reduction were measured at the warmest temperate site. Potential rates of extracellular enzymatic hydrolysis (at least for this class of pullulanase enzymes) do not appear to Limit organic carbon turnover in the Arctic. These results suggest that organic carbon turnover in the cold Arctic is not intrinsically slower than carbon turnover in temperate environments; sedimentary metabolism in Arctic sediments may be controlled more by organic matter supply than by temperature.
