Observation of sulfate crystallites in Vostok accretion ice

Controlled sublimation in a low-vacuum scanning electron microscope has been used to reveal unusual crystalline features in the triple junctions of accretion ice from the Antarctic ice sheet above Lake Vostok. Energy dispersive X-ray microanalysis showed that the features were composed mostly of magnesium, sulfur and oxygen, although small amounts of sodium and calcium were also occasionally observed. Synchrotron X-ray topography showed that the ice grains contained dislocation densities ranging from ∼1×107 to >1×1010 m−2.