  Single crystals of ice Ih, extracted from the subglacial Lake Vostok
accretion ice layer (3621 m depth) were investigated by means of diffuse x-ray
scattering and inelastic x-ray scattering. The diffuse scattering was
identified as mainly inelastic and rationalized in the frame of ab initio
calculations for the ordered ice XI approximant. Together with Monte-Carlo
modelling our data allowed reconsidering previously available neutron diffuse
scattering data of heavy ice as the sum of thermal diffuse scattering and
static disorder contribution.
