Stable Isotope Fractionation of Nitrogen between Gas and Hydrate Phases

Abstract

Stable isotope ratios of nitrogen gas in ice core air samples represent a valuable tool for studying the past climate change. In this study, we investigated the stable isotope fractionation of nitrogen between the gas and hydrate phases during nitrogen hydrate formation. Nitrogen hydrate samples were formed in the temperature range of 225–271 K and pressure range of 13–19 MPa. The isotopic compositions of the original, residual (unreacted), and hydrate-bound gases were measured. The nitrogen isotope ratio of the hydrate-bound gas was greater than that of the residual gas by 0.2‰, indicating that the nitrogen hydrate was slightly more susceptible to 14N15N inclusion. This suggests that the equilibrium pressure of the 14N15N hydrate is slightly lower than that of the 14N2 hydrate.