An empirical model of firn densification from the surface to the zone of pore close-off has been constructed. Fundamental rate equations have been derived for the first two stages of densification. In the first stage, for densities less than 0.55 Mg m−3, the densification rate is proportional to the mean annual accumulation times the term (ρi−ρ), whereρis the density of the snow andρiis the density of pure ice. The densification rate in the second stage, where 0.55 Mg m−3< ρ < 0.8 Mg m−3, is proportional to the square root of the accumulation rate and to (ρi−ρ). Depth–density and depth–age calculations from this model are compared with observation. Model accumulation rates are within about 20% of values obtained by other techniques. It is suggested that depth intervals of constant density in some Antarctic cores may represent a synchronous event in the 1880 ’s when ten times the normal accumulation fell within a year or two.

ABSTRACT. An empirical model offirn densification from the surface to the zone of pore close-off has been constructed. Fundamental rate equations have been derived for the first two stages of densification. In the first stage, for densities less than 0.55 Mg m -J , the densification rate is proportional to the mean annual accumulation times the term ( pI-p), where p is the density of the snow and Pi is the density of pure ice.The densification rate in the second stage, where 0.55 Mg m -J < p < 0.8 Mg m -J , is proportional to the square root of the accumulation rate and to ( pi -p). Depth-density and depth-age calculations from this model are compared with observation. Model accumulation rates are within about 20 % of values obtained by other techniques. It is suggested that depth intervals of constant density in some Antarctic cores may represent a synchronous event in the 1880'S when ten times the normal accumulation fell within a year or two. RESUME. DelZsificatiolZ du neve: un modele empirique. On a construit un modele empirique de la densification du neve depuis la surface jusqu'a la zone de fermeture des pores. Dans le premier stade, pour des densites inferieures a 0,55 Mg/m-" la vitesse de densification est proportionnelle au produit de l'accumulation moyenne annuelle par le terme (PI -p), OU P est la densite de la neige et PI la densite de la glace pure. gilt, ist proportional zur Quadratwurzel aus der Akkumulationsrate, multipliziert mit (Pi -p). Berechnungen der Dichte und des Alters mit der Tiefe aus diesem Modell werden mit Beobachtungen verglichen. Die Modell-Akkumulationsraten stimmen auf etwa 20 % mit Werten uberein, die mit anderen Methoden gewonnen wurden. Die Annahme erscheint gerechtfertigt, dass Intervalle konstanter Dichte in einigen antarktischen Eiskernen aus einem gleichzeitigen Ereignis in den 80er Jahren des letzten Jahrhunderts stammen, bei dem innerhalb eines Jahr, es od er zweier die Akkumulation zehnmal grosser war als sonst.

No abstract

A correlation of time with depth has been evaluated for the Camp Century, Greenland, 1390 meter deep ice core. Oxygen isotopes in approximately 1600 samples throughout the core have been analyzed. Long-term variations in the isotopic composition of the ice reflect the climatic changes during the past nearly 100,000 years. Climatic oscillations with periods of 120, 940, and 13,000 years are observed.