Quaternary Research 57, 225–233 (2002) doi:10.1006/qres.2001.2308, available online at http://www.idealibrary.com on Holocene Lake-Effect Precipitation in Northern Michigan Paul A. Delcourt Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996 Peter L. Nester 1 Department of Geological Sciences, University of Tennessee, Knoxville, Tennessee 37996 Hazel R. Delcourt Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996 Claudia I. Mora Department of Geological Sciences, University of Tennessee, Knoxville, Tennessee 37996 and Kenneth H. Orvis Department of Geography, University of Tennessee, Knoxville, Tennessee 37996 Received March 29, 1999; published online February 5, 2002 Holocene sediments from Nelson Lake, on Michigan’s eastern Upper Peninsula, provide isotopic, pollen, and charcoal evidence for a two-step sequence of changes in moisture source and increased lake-effect precipitation during the late Holocene. Between 8000 and 5300 cal yr B.P., a warm, dry climate and zonal atmospheric circulation produced enriched stable oxygen and carbon isotopic values in combination with high percentages of pine pollen and sustained influx of charcoal particles. After 5300 cal yr B.P., de- creasing isotopic values in marl and increasing pollen percentages of mesic hardwoods and northern white cedar indicate increased meridional air flow and precipitation from cold winter storms gen- erated in Alberta, Canada. After 3000 cal yr B.P., abrupt declines in values of δ 13 C and δ 18 O and increased pollen representation of hemlock, American beech, spruce, and aquatic plants indicate paludification from increased lake-effect snowfall. The moisture was derived from the Great Lakes and transported by Alberta cy- clonic storms that were steered across Lakes Superior and Michigan by a southward shift in the modal winter position of the polar jet stream. C  2002 University of Washington. Key Words: climate change; paleoecology; stable isotope. INTRODUCTION In the upper Midwest region of North America, the climate changed from warm and dry to cooler, wetter conditions af- 1 Current address: Paleontological Research Institution, 129 Trumansburg Road, Ithaca, New York 14850. ter about 5000 cal yr B.P., reflecting a subcontinental-scale shift from zonal to meridional atmospheric circulation patterns (Winkler et al., 1986; Wright, 1992; Kutzbach et al., 1993; Dean et al., 1996). Late Holocene paludification has been attributed largely to increased precipitation accompanying a southward shift in the modal winter position of the polar jet stream (Webb et al., 1993; Brugam and Swain, 2000; Lavoie and Richard, 2000). Stable isotope studies indicate a 1 ◦ –3 ◦ C decrease in mean annual temperature (Dean and Stuiver, 1993; Yu et al., 1997; Edwards et al., 1996). The Great Lakes influence mesoscale climate by moderat- ing near-shore temperatures and providing a moisture source for lake-effect precipitation (Phillips and McCulloch, 1972; Eichenlaub et al., 1990). Lake-effect snowfall >1.5 m typically extends 100 km inland (Fig. 1) along the southern and east- ern shores of Lake Superior and other Great Lakes (Norton and Bolsenga, 1993). From November through March, frigid Cana- dian airmasses absorb water vapor from ice-free lake surfaces (Fig. 2). Lake-effect snowfall deposited downwind has sharply depleted δ 18 O values, typically 10‰ lower than summer rainfall values (Machavaram and Krishnamurthy, 1992). The Holocene history of lake-effect snowfall can be inferred from stable isotopic studies of the sediments of lakes within the present-day influence of the Great Lakes. To determine the tim- ing of onset in lake-effect mesoclimate, we studied the Holocene sediment record from Nelson Lake, located 15 km north of Lake Michigan, 50 km south of Lake Superior, and 55 km west of Lake Huron along the east–west drainage divide of the Niagara 225 0033-5894/02 $35.00 Copyright C  2002 by the University of Washington. All rights of reproduction in any form reserved.