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Thermal Regimen of Firn on Upper Seward Glacier, Yukon Territory, Canada*

  • Robert P. Sharp (a1)
Abstract

Temperatures were measured within the firn and ice of the upper reaches of the Seward Glacier (referred to in this paper as the “upper Seward Glacier”) to a depth of 204 ft. (62.2 m.) by means of thermohms and a Wheatstone bridge. Thermal boring proved a feasible means of penetrating this glacier. The winter’s chilled layer here develops a thickness of 40–50 ft. (12.2–15.2 m.) and attains temperatures of at least −13° C. Deterioration of the chilled Iayer is rapid and irregular in the final phase and is attributed largely to freezing of percolating melt water. Melt water exerts such a powerful influence on thermal regimen that bodies of firn in environments with mean annual temperatures below freezing may, nonetheless, be geophyaically temperate because of extensive warming by melt water in summer. In both 1948 and 1949, the annual chilled layer on the upper Seward Glacier disappeared within the first 10 days of July. The slow development and rapid deterioration of diurnal crusts on firn and the lag effects at depth reproduce in miniature the behavior of the annual chilled layer. On the basis of its thermal regimen the upper Seward Glacier is geophysically temperate.

Zusammenfassung

Temperaturen in Firn und Eis in dem oberem Teil des Seward Glacier wurden bis zu einer Tiefe von 62.2 Metern mittels “Thermohms” und einer Wheatstoneschen Brücke gemessen. Thermische Bohrungen erwiesen sich als geeignete Mittel, um in diesen Gletscher einzudringen. Die Frostschicht des Winters entwickelt hier eine Dicke von 12.2–15.2 Metern und erreicht Temperaturen von mindestens −13° C. Der Verfall der Frostschicht geht schnell, in der letzten Phase unregelmässig vor sich und wird hauptsächlich auf das Gefrieren von durchsickerndem Schmelzwasser zurückgeführt. Schmelzwasser übt einen derartig starken Einfluss auf den thermischen Haushalt aus, dass Firnmassen im Bereich von Durchschnittstemperaturen unter Null gemässigt sein können, weil das Schmelzwasser im Sommer ausserordentlich wärmend wirkt. Sowohl im Jahre 1948 wie auch 1949 verschwand die Jahresfrostschicht von diesem Gletscher innerhalb der ersten 10 Tage im Juli. Die langsame Entwicklung und der schnelle Verfall von dem auf Fim gebildeten Tagesharsch und die verzögernden Wirkungen in der Tiefe geben im Kleinen das Verhalten der jahresfrostschicht wieder. Auf Grund seiner thermischen Reaktion ist dieser Gletscher gemässigt.

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Copyright
Footnotes
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Division of Geological Sciences, California Institute of Technology, Contribution Number 343.

Footnotes
References
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1. Ahlmann, H. W:son. Glaciological research on the North Atlantic coasts. Royal Geographical Society, Research Series No. 1, 1948, p. 66.
2. Sverdrup, H. U. The temperature of the fim on Isachsen’s Plateau, and general conclusions regarding temperature of the glaciers on West-Spitsbergen. Geografiska Annaler, Vol. 17, Ht. 1–2, 1935, p. 5388.
3. Hughes, T. P. Seligman, Gerald. The temperature, melt water movement, and density increase in the névé of an alpine glacier. Royal Astronomical Society, Monthly Notices, Geophysical Supplement, Vol. 4, No. 8, 1939, p. 65634.
4. (a) Chamberlin, T. C. A contribution to the theory of glacial motion. University of Chicago, Decennial Publications, 1st Series, Vol. 9, 1904, p. 196200.
(b) Chamberlin, T. C. Salisbury, R. D. Geology. Vol. 1—Geologic processes and their results. New York: Henry Holt and Co., 1909, p. 27379.
5. Drygalski, Erich v. Machatschek, Fritz. Gletscherkunde, Enzykloplidie der Erdkunde. Vienna: Deuticke, 1942, p. 8485
6. Matthes, F. E. Glaciers, Chapt. V in Hydrology—Physics of the Earth, Vol. 9, New York: McGraw-Hill, 1942,p. 152.
7. Wade, F. A. The physical aspects of the Ross Shelf Ice. Proceedings of the American Philosophical Society, Vol. 89, No. 1, 1945. p. 16970.
8.Sub-surface temperature measuring equipment. Journal of Glaciology, Vol. 1, No. 2, 1947, p. 7374.
9. Court, Arnold. Temperature measurements in polar ice. Journal of Glaciology, Vol. 1, No. 5, 1949, p. 228.
10. Sverdrup., Ref. 2, p. 53, 59.
11. Hughes, Seligman, . Ref. 3, p. 659.
12. Perutz, M. F. Direct measurement of the velocity distribution in a vertical profile through a glacier. Journal of Glaciology, Vol. 1, No. 7,1950, p. 38283.
13. Court., Ref. 9, p. 22730.
14. Ahlmann, . Ref. 1, p. 66.
15. Hughes, Seligman, . Ref. 3, p. 622, 625.
16. Drygalski, Machatschek, . Ref. 5, p. 83.
17. Wade, . Ref. 7, p. 167.
18. Sorge, Ernst. The scientific results of the Wegener expeditions to Greenland. Geographical Journal, Vol. 81, 1933, p. 339.
19. Chamberlin, . Ref. 4.
20. Sverdrup., Ref. 2, p. 71.
21. (a) Ibid.
(b) Gerdel, R. W. Penetration of radiation into the snow pack. Transactions, American Geophysical Union, Vol. 29, 1948, p. 370.
(c) Work, R. A. Snow-layer density changes. Transactions, American Geophysical Union, Vol. 29, 1948, p. 543.
22. (a) Sverdrup., Ref. 2, p. 71.
(b) Hughes, Seligman, . Ref. 3, p. 62226.
23. Seligman, Gerald. Snow structure and ski fields. London: Macmillan, 1936, p. 27880.
24. Hughes, Seligman, . Ref. 3, p. 634.
25. (a) Glen, A. R. The Oxford University Arctic expedition, North East Land, 5935–36. Geographical Journal, Vol. 90, Nos. 3–4, 1937, p. 22021.
(b) Moss, Robert. The physics of an icecap. Geographical Journal, Vol. 92, No. 3, 1938, p. 222.
26. Chamberlin, . Ref. 4 (a), p. 198,1904; 4 (b), p. 274, 1909.
27. (a) Sverdrup., Ref. 2, p. 54.
(b) Hughes, Seligman, . Ref. 3, p. 622.
(c) Wade., Ref. 7, p. 569.
(d) Sorge., Ref. 18, p. 339.
28. (a) Hughes, Seligman, . Ref. 3, p. 62631.
(b) Sverdrup., Ref. 2, p. 7678.
29. (a) ― Ref. 2, p. 70.
(b) Hughes, Seligman, . Ref. 3, p. 62126.
30. Sverdrup, . Ref. 2, p. 8287.
31. (a) ― Ref. 2, p. 82.
(b) Gerdel, . Ref. 21, p. 366.
32. Sverdrup, . Ref. 2, p. 84.
33. — Ref. 2, p. 8687.
34. (a) Low, A. P. Report on the Dominion Government expedition to Hudson Bay and the Arctic Islands on board the D.G.S. Neptune, 1903–1904, Ottawa, 1906, p. 8687.
(b) Bernier, J. E. Report on the Dominion of Canada government expedition to the Arctic islands and Hudson Strait on board the D.G.S. Arctic, Ottawa, 1910, p. 343.
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