Middle Wisconsinan Climate Fluctuations Recorded in Central Alaskan Loess

Fluctuations in Middle Wisconsinan environments are recorded in high resolution proxy climatic curves derived from magnetic susceptibility profiling of central Alaskan loess. Two intervals of low wind intensity and climatic amelioration, separated by a period of somewhat higher wind intensity, can b...

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Bibliographic Details
Published in:Géographie physique et Quaternaire
Main Author: Begét, Jim
Format: Text
Language:English
Published: Les Presses de l'Université de Montréal 1990
Subjects:
Ice
Online Access:http://id.erudit.org/iderudit/032793ar
https://doi.org/10.7202/032793ar
Description
Summary:Fluctuations in Middle Wisconsinan environments are recorded in high resolution proxy climatic curves derived from magnetic susceptibility profiling of central Alaskan loess. Two intervals of low wind intensity and climatic amelioration, separated by a period of somewhat higher wind intensity, can be recognized in several loess records of the Middle Wisconsinan. Radiocarbon dates from loess in the Fox Permafrost Tunnel indicate that the culmination of the later period of low wind intensity occurred ca. 30-32.000 yr BP, and was associated with thermal degradation of permafrost. An older period of low wind intensity early in the Middle Wisconsinan, ca. 50-60,000 yr BP, is correlative with a fossil wood horizon in the permafrost tunnel and a widespread paleosol in loess sections. Warm intervals of similar age are recorded in the Grande Pile pollen record, in ice cores and in marines cores. The 30-32,000 yr BP and the 50-60,000 yr BP warm events recorded in Alaskan loess sequences may have been caused by "greenhouse" warming produced by transient increases in atmospheric CO2 as recorded in the Vostok ice core. A Middle Wisconsinan interval of higher wind intensity, associated with the development of ice wedges, may reflect climatic cooling due to low atmospheric CO2 values ca. 42,000 yr BP. Les courbes climatiques très précises tracées à partir des profils de susceptibilité magnétique faites sur le loess du centre de l'Alaska ont montré des fluctuations au Wisconsinien moyen. Deux intervalles de vents de faible intensité et de réchauffement climatique, séparés par une période de vents plus forts, ont pu être reconstitués à partir de plusieurs inventaires loessiques du Wisconsinien moyen. Les dates au radiocarbone recueillies sur le loess du Fox Permafrost Tunnel montre que l'optimum de la dernière période de vents faibles a eu lieu vers 30-32 ka BP, et qu'il était associé à une régression du pergélisol. Une période plus ancienne de vents faibles au début du Wisconsinien moyen (vers 50-60 ka BP) correspond à un ...