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Rate of Growth or Shrinkage of Nonequilibrium Ice Sheets

  • J. Weertman (a1)

Abstract

An analysis is made of the time required to build up an ice-age ice sheet and of the time required to destroy such an ice sheet. The calculations are based on the approximation that the theory of perfect plasticity is valid. It is concluded that the time required to build up an ice-age ice sheet is longer than the time required to eliminate it. If it is assumed that the accumulation rate of an ice-age ice sheet lies in the range of 0.2 to 0.6 m./yr., it is found that the growth time of a large ice sheet is of the order of 15,000 to 30,000 yr. Ablation rates of to 2 m./yr. lead to shrinkage times of the order of 2,000 to 4,000 yr., provided ablation occurs over an appreciable area of the ice sheet.

Résumé

On analyse le temps nécessaire à l’établissement d’une calotte de glace et à sa disparition. Les calculs sont basés sur l’approximation que la théorie des corps parfaitement plastiques est valable. On en conclut que le temps requis pour édifier une calotte de glace, est plus grand que le temps nécessaire à sa destruction. Si l’on admet que le taux d’accumulation d’une calotte de glace est compris entre 0,2 et 0,6 m/an, on trouve que le temps de croissance d’une calotte étendue est de l’ordre de 15 000 à 30 000 ans. D’autre part, si l’on admet un taux d’ablation de 1 à 2 m/an, on est conduit à un temps de disparition de l’ordre de 2 000 à 4 000 ans à condition qu’il y ait ablation sur une surface appréciàble de la calotte.

Zusammenfassung

Die vorliegende Untersuchung gilt der Frage, in welchen Zeiträumen ein eiszeitlicher Eisschild entstehen bzw. verschwinden kann. Die Bcrcchnungen beruhen auf der Näherungsannahme, dass die Theorie der vollständigen Plastizität gültig ist. Man kann dann folgern, dass der Aufbau eines eiszeitlichen Eisschildes eine längere Zeit beansprucht als sein Abbau. Unter der Annahme eines jährlichen Auftrages von 0.2–0.6 m ergibt sich für einen grossen Eisschild eine Bildungszeit von 15 000–30 000 Jahren. Ein Abtrag von 1–2 m pro Jahr führt zu Abbauzeiten in der Grössenordnung von 2000–4000 Jahren, vorausgesetzt, dass über einem beträchtlichen Teil des Eisschildes Ablation herrscht.

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Copyright

References

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