Interpretation of the small grains in the inclusions of ice cores

The origin of the grains with diameters less than 4 μm from the inclusions in Antarctic ice cores is discussed. It is proposed that these grains were initiated by ions stopped in the upper atmosphere. The ions form molecules, which coagulate and diffuse downwards. These processes give rise to a characteristic mass spectrum of the small grains. Inclusions in ice were abundant during cold periods of the Pleistocene. This supports a model in which the influx of particles is large when Earth’s orbit stays within a disk shaped cloud around the Sun. The production of such a cloud may favor light atoms. This should e.g. be apparent in the isotope distribution of Magnesium from the small grains. The large grains, which have a variable mass distribution, are terrestrial.