Kinetic nitrogen isotope fractionation between air and dissolved N2 in water: Implications for hydrothermal systems

To conduct the experiment, 1 L beakers filled with distilled water and exposed to air were heated with a hot plate and cooled down with ice to reach the desired temperatures (5, 20, 40, and 60∞C). After the water samples had reached the desired temperatures, they were continuously aerated with ambient air that had a d15N value of 0.0‰ by an aquarium air pump (Aqua Culture, flow rate: 1.2 L/minute) for 20~30 minutes. 20 mL glass vials equipped with rubber septa and metal caps were used to sample the water. It was critical that vials were filled and capped underwater in order to prevent any ambient air contamination. Sampling was repeated until there were no air bubbles observed in the vials. After collection, the vials were flushed with helium (He) in order to obtain a headspace (8 ml). The flushing was performed by a 5 cm long needle with two holes inserted through the septum. The needle was used to inject He and extract water simultaneously. Each vial was filled with the same amount of He gas as recorded by the displacement of the water, which was approximately 5 ml. Then the vial was shaken Kinetic nitrogen isotope fractionation between air and dissolved N2 in water: Implications for hydrothermal systems