Enclosure of Air During Metamorphosis of Dry Firn to Ice

Abstract

If cold firn has reached a density of about 0.55 Mg m-3, further densificaron occurs by a sintering process which increases the contact surface between the firn grains. The pore volume is decreasing continuously but the firn remains permeable to air up to a density of 0.82 Mg m-3. At about this density the remaining air in the pore volume is closed off in isolated bubbles. We are interested in the age and the age distribution of the air enclosed in bubbles relative to the age of the surrounding ice, and are investigating the development of the pore volume in firn. A newly constructed measuring device allows the field measurement of the amount of air which is already enclosed in bubbles of firn samples. Measurements have been made during summer 1983 in Greenland and during winter 1983/84 at the South Pole. The results are discussed and compared with results obtained with a simplified statistical sintering model, using some results of percolation theory.