Abstract
Clathrate hydrates of methane and other small alkanes occur widespread terrestrially in marine
sediments of the continental margins and in permafrost sediments of the arctic. Quantitative study of
natural clathrate hydrates is hampered by the difficulty in obtaining pristine samples, particularly from
submarine environments. Bringing samples of clathrate hydrate from the seafloor at depths without
compromising their integrity is not trivial. Most physical property measurements are based on studies
of laboratory-synthesized samples. Here we report X-ray powder diffraction measurements of a natural
gas hydrate sample from the Green Canyon, Gulf of Mexico. The first data were collected in 2002 and
revealed ice and structure II gas hydrate. In the subsequent time the sample has been stored in liquid
nitrogen. More recent X-ray powder diffraction data have been collected as functions of temperature
and time. This new data indicates that the larger sample is heterogeneous in ice content and shows that
the amount of sII hydrate decreases with increasing temperature and time as expected. However, the
dissociation rate is higher at lower temperatures and earlier in the experiment.
