A 8500-YEAR RECORD OF LAKE-EFFECT CLIMATE FROM MINER LAKE, SOUTHWESTERN LOWER MICHIGAN

Miner Lake (42.7°N, 85.8°W) in Allegan County, southwestern Lower Michigan, is located 30 km east of Lake Michigan. Today, the local vegetation is comprised of primarily beech-maple forest and has a lake-mediated climate characterized by higher snowfall and warmer winter temperatures than inland locations. The objective of our research was to test whether the lake-effect climate in the past was a more dominant influence on the local climate of the Miner Lake area than regional paleoclimate patterns. We did this by analyzing sediment cores from Miner Lake for pollen, plant macrofossils and sedimentology (particle size, % organic matter (OM), and % calcium carbonate (CaCO₃)), and compared these data to paleoclimate data from two lakes from inland locations with similar latitudes.

Over the past 8500 cal yr BP, the sedimentology and paleobotany of Miner Lake indicate that there has been little environmental change in the area. In general, the %OM increases from ~25 to 40%, %CaCO₃ decreases from ~20 to 10% and the median grain size ranges from ~10 to 25 microns. The high %OM and CaCO₃, and fine median grain size in the sediments of Miner Lake suggest that this lake received little influx of clastic material. The pollen and plant macrofossil records indicate four intervals of vegetation change. A pine-oak forest characterizes Zone I (~8500 to 7000 cal yr BP), prior to the arrival of beech in the region. Zone II (~7000-3200 cal yr BP) is that of a beech-maple forest with oak patches. Percentages of beech and maple are higher than in the two comparative pollen records, indicating that moisture provided by the lake-effect climate prevailed in the Miner Lake area during the peak Holocene warmth. Zone III (~3200-200 cal yr BP) is characterized by cooler and moister conditions, as suggested by expansion of the beech-maple forest. Median grain size is most variable in Zone III. Zone IV (last 200 years) is distinguished by a spike in disturbance weeds, a sharp decrease in %OM, a dramatic increase in %CaCO₃, and a sharp decrease in median grain size, likely resulting from agriculture. In summary, the paleoclimate record of Miner Lake was, for the most part, invariant during the past several millennia, which suggests that a “lake effect” climate induced by nearby Lake Michigan was a more dominant control than the regional climate for this site.