Continental-scale climate forcing factors and environmental change at Glimmerglass Lake in the upper Peninsula of Michigan

Abstract

Previous palaeoecological studies have shown that there have been major range shifts in Tsuga (hemlock) during the middle and late Holocene that seem to indicate climatic cooling and an increase in available moisture. We examined lake-level changes and peatland growth at Glimmerglass Lake and peatland in the Sylvania Wilderness Area to determine if the mid-Holocene increase in moisture indicated by the pollen record also influenced lakes and wetlands. Sphagnum peat began accumulating at the site at 6240 cal. yr BP. Diatom-inferred depth reconstructions show that the lake level rose 2 m and the peatland expanded out of its basin at 5300 cal. yr BP. All of these changes occurred as the last remnant of the Laurentide Ice Sheet disappeared and orbital forcing reduced seasonality relative to the early Holocene. We conclude that these continental-scale factors caused increased moisture availability in the Upper Peninsula of Michigan, resulting in rising lakewater levels and peatland expansion.