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The Mass Balance of the Sea Ice of the Arctic Ocean

  • R. M. Koerner (a1)
Abstract

From data taken on the British Trans-Arctic Expedition it is calculated that 9% of the Arctic Ocean surface between the North Pole and Spitsbergen was hummocked or ridged ice, 17% was unridged ice less than a year old, 73% was unridged old ice and 0.6% was ice-free. The mode of 250 thickness measurements taken through level areas of old floes along the entire traverse lies between 2.25 and 2.75 m. The mean end-of-winter thickness of the ice is calculated to be 4.6 m in the Pacific Gyral and 3.9 m in the Trans-Polar Drift Stream. From measurements of the percentage coverage and thickness of the various ice forms, it is calculated that the total annual ice accumulation in the Arctic Ocean is equivalent to a continuous layer of ice 1.1 m thick. 47% of this accumulation occurs in ice-free areas and under ice less than 1 year old. 20% of the total ice production is either directly or indirectly related to ridging or hummocking. An ice-ablation rate of 500 kg m−2 measured on a level area of a multi-year floe is compared with the rate on deformed and ponded ice. Greatest melting occurs on new hummocks and least on old smooth hummocks. The annual balance of ice older than 1 year but younger than multi-year ice is calculated from a knowledge of ice-drift patterns and the percentage coverage of first-year ice. The same calculations give a mean-maximum drift period of 5 years for ice in the Trans-Polar Drift Stream and 16 years in the Pacific Gyral. It is calculated that for the period February 1968 to May 1969 the annual ice export was 5 580 km3.

Résumé

A partir de données recueillies par l’expédition trans-Arctique britannique, on a calculé que 9% de la surface de l’Océan Arctique entre le Pôle Nord et le Spitsbergen était occupé par de la glace en hummock ou ridée, 17% étant de la glace non ridée de moins d’un an, 73% de la vieille glace non ridée et 0,6% libre de la glace. Le résultat des 250 mesures d’épaisseur prises à travers les zones plates de la vieille banquise tout au long de la traversée reste compris entre 2,25 et 2,75 m. L’épaisseur moyenne de fin d’hiver est, d’après les calculs, de 4,6 m dans le tourbillon Pacifique et de 3,9m dans le “Trans-Polar Drift Stream”. Les mesures du taux de couverture et de l’épaisseur des différentes formes de glace permettent de calculer que l’accumulation totale annuelle de la glace est épaisse de 1,1 m. 47% de cette accumulation se produit dans des zones libres de glace et sous une glace vieille de moins d’un an. 20% de la production totale de glace est directement ou indirectement liée à la formation de rides ou de hummock. Un taux d'ablation de la glace de 500 kg m −2 mesuré sur une aire plate d’une banquise pluriannuelle est comparé avec le taux sur de la glace déformée ou chargée. La fusion la plus intense est observée sur les hummocks de formation récente, la moins intense sur les hummocks vieux aux formes adoucies. Le bilan annuel de la glace de plus d’un an, mais plus jeune que les glaces multiannuelles, est calculé d’après une connaissance des mouvements de la glace et le pourcentage de couverture de la glace de première année. Les mêmes calculs donnent une moyenne de 5 ans pour la période maximum de transport par le vent dans le “Trans-Polar Drift Stream” et de 16 ans dans le tourbillon Pacifique. On a calculé que pour la période de février 1968 à mai 1969, l’exportation annuelle de glace était de 5 580 km3.

Zusammenfassung

Aus den bei der britischen Trans-Arktis-Expedition gewonnenen Daten wurde errechnet, dass 9% der Oberfläche des Arktischen Ozeans zwischen dem Nordpol und Spitsbergen mit buckligem oder aufgewölbtem Eis, 17% mit rückenfreiem Eis von weniger als einem Jahr Alter, 73% mit rückenfreiem, altem Eis bedeckt und 0,6% eisfrei waren. Der Hauptteil der 250 Dickenmessungen an ebenen, alten Eisschollen entlang der gesamten Route ergab Dicken zwischen 2,25 m und 2,75 m. Die mittlere Eisdicke am Winterende wurde für das Pazifische Becken zu 4,6 m und im Transpolaren Driftstrom zu 3,9 m errechnet. Aus Messungen der prozentualen Bedeckung und Dicke der verschiedenen Eisarten ergibt sich, dass die gesamte jährliche Eisakkumulation im Arktischen Ozean einer gleichmässigen Eisschicht von 1,1 m Dicke entspricht. 47% dieser Akkumulation erfolgt in eisfreien Gebieten oder unter Eis von weniger als einem Jahr Alter. 20% der gesamten Eisproduktion sind entweder direkt oder indirekt mit der Bildung von Rücken oder Buckeln verbunden. Die Ablationsrate von 500 kg m−2, die in einem ebenen Gebiet einer mehrere Jahre alten Eisscholle ermittelt wurde, wird mit der Rate für deformiertes und Wasserlachen bildendes Eis verglichen. Die stärkste Abschmelzung tritt an neuen, die geringste an alten, flachen Eisbuckeln auf. Die Jahresbilanz von Eis zwischen einem und mehreren Jahren Alter wurde aus der Kenntnis der Eisdriftsysteme und der prozentualen Bedeckung mit einjährigem Eis berechnet. Dieselben Berechnungen ergeben eine mittlere Maximaldriftperiode von 5 Jahren für Eis im Transpolaren Driftstrom und von 16 Jahren im Pazifischen Becken. Für die Periode von Februar 1968 bis Mai 1969 wurde ein jährlicher Eisausstoss von 5 580 km3 errechnet.

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References
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Journal of Glaciology
  • ISSN: 0022-1430
  • EISSN: 1727-5652
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