EVIDENCE FOR CLIMATE CHANGE SINCE THE LAST GLACIAL MAXIMUM: A MULTI-PROXY STUDY OF DUCK LAKE, SOUTH-CENTRAL MICHIGAN

Terrestrial and aquatic environments in the Great Lakes region have undergone significant changes in response to past climate change and anthropogenic disturbances. Duck Lake in south-central Michigan is the focus of a multi-proxy study to identify these changes and examine their relationship to regional climate variations and local land use variations. Duck Lake is a 254-hectare lake with a maximum depth of 15 meters and has no major inlets and only one major outlet on its northern shore. The lake is located in Calhoun County in the interior of the Lower Peninsula, an ideal location to minimize the effects of lake-effect climates. Extensive development dominates Duck Lake's shorelines and both agricultural and forested areas are found within a mile of the shore. A Livingstone piston corer was used to collect cores with overlapping drives about 1 meter apart to a depth of 11 meters and captured the sediment transition from inorganic (late-glacial) to organic (early Holocene). Samples were also taken at the sediment-water interface using the freeze-core method. Volume magnetic susceptibility values of zero were obtained over the top 9 meters, suggesting no major changes in source area over the time of deposition. X-radiographs of the Livingston cores show approximately 1.5 meters of laminated sediments, millimeters thick, at depths of 7.5 to 9 meters. Alternating silt and clay layers, 5 to 10 centimeters thick, are found from the surface to a depth of about 7.5 meters. These layers may represent changes in the energy of deposition or sediment gravity deposits. Initial estimates of 90.0 ± 30 cm/kyr sediment accumulation have been made for the 11-meter core section, although this estimate will become more refined with detailed radiocarbon chronology. Other analyses to be performed on these sediments include loss-on-ignition, bulk geochemistry, mercury analysis, phosphorus extraction and particle size analysis. The study of these proxies from Duck Lake will provide evidence for environmental change by which future predictions of long-term climate change for the southern Great Lakes region can be made.