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Mid-Holocene Climate in Northern Minnesota

Published online by Cambridge University Press:  20 January 2017

Richard M. Forester
Affiliation:
U.S. Geological Survey, MS 919, Denver, Colorado 80225, USA
L. Denis Delorme
Affiliation:
NWRI, P.O. Box 5050, Burlington, Ontario, Canada L7R 4A6
J. Platt Bradbury
Affiliation:
U.S. Geological Survey, MS 919, Denver, Colorado 80225, USA

Abstract

Study of Holocene ostracodes and diatoms from Elk Lake, in North-Central Minnesota, indicates that the local climate of the mid-Holocene can be subdivided into three intervals. Throughout interval 1 (ca. 7800 to 6700 yr B.P.), climate was colder and much drier than today. During intervals 2 and 3 (ca. 6700 to 4000 yr B.P.) average mean-annual air temperatures approached the modern mean (3.7°C), but warm summers persisted throughout interval 2, whereas during interval 3 warm summers fell into discrete episodes. Furthermore, average mean-annual precipitation was about 85 and 90% of modern during intervals 2 and 3, respectively. Transition times between the principal intervals were less than 50 yr. The expected effects of a retreating Laurentide Ice Sheet that initially maintained a winter-style circulation, followed by transitional climate states, and finally a near-modern circulation pattern may explain these local climatic events.

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Type
Articles
Copyright
University of Washington

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