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Middle Holocene Dry Period in the Northern Midwestern United States: Lake Levels and Pollen Stratigraphy

Published online by Cambridge University Press:  20 January 2017

M. G. Winkler
Affiliation:
IES-Center for Climatic Research, University of Wisconsin, 1225 West Dayton Street, Madison, Wisconsin 53706 USA
A. M. Swain
Affiliation:
IES-Center for Climatic Research, University of Wisconsin, 1225 West Dayton Street, Madison, Wisconsin 53706 USA
J. E. Kutzbach
Affiliation:
IES-Center for Climatic Research, University of Wisconsin, 1225 West Dayton Street, Madison, Wisconsin 53706 USA

Abstract

Four cores from Lake Mendota in the Yahara River valley of south-central Wisconsin provide pollen, charcoal, and sediment-year. Derived estimates of stratigraphic evidence of a middle Holocene dry period in the northern Midwest. The lake level was lower between about 6500 and 3500 yr B.P. indicating that runoff from the upper Yahara River basin may have ceased during the drier seasons of the precipitation between 6500 and 3500 yr B.P. indicate a decrease of about 10% (down to about 700 mm) from the present precipitation value of 800 mm. A warming between 6500 and 3500 yr B.P. is also interpreted based on a change of vegetation from rich mesophytic forest before 6500 yr B.P. to Quercus savanna, with increased charcoal abundances after that time. After 3500 yr B.P., a closed Quercus forest and decreased charcoal suggest a cooler and wetter climate. The qualitative paleoecological interpretations, quantitative precipitation reconstructions based on pollen from the region (including the Lake Mendota data), and estimates of hydrologic budget based on lake-level changes, all show indications of a dry and warm middle Holocene. Evidence from a large regional array of sites also supports these interpretations.

Information

Type
Original Articles
Copyright
University of Washington

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