Stratigraphic Evidence of Water-level Changes in Small Lakes in the Southern Great Lakes Region and Adjacent Allegheny Plateau during the Late-Quaternary

Abstract:

During the Holocene, the southern Great Lakes region experienced regional hydroclimate changes that may have had long-term impacts on the vegetation there, including the abrupt decline of the beech tree, Fagus grandifolia. These vegetation changes may represent the regional effects of repeated multi-century droughts over the past 5,000 years, which have been previously documented along the North Atlantic coast of eastern North America. By quantitatively tracking the elevation of the sand-mud boundary, we can create lake-level timeseries, and study the extent and timing of droughts. Here, we present two water-level reconstructions from small lakes along the Michigan-Indiana border and the Allegheny Plateau region of Pennsylvania. These reconstructions were developed using ground-penetrating radar (GPR) profiles and sediment grainsize analysis to identify paleoshorelines. The stratigraphic features at Lake Lavine in Michigan and Sunfish Pond in Pennsylvania indicate that, especially before ca. 2 ka., both lakes experienced periods when water levels were substantially lower than today. At Sunfish Pond, a sand layer extending out from shore to 200 – 400 cm below the modern water level indicates an extended period of low water levels in the mid-Holocene. At Lake Lavine, four distinct sand layers located between 175 – 400 cm below the modern water level also suggest fluctuations in the local hydrologic budget. Calibrated radiocarbon ages constrain timing of paleoshoreline deposition and enables evaluation of the east-west geographic extent of the century-to-millennia long periods of drought recorded in New England and their connection to vegetation changes in the southern Great Lakes region.