PARENT SESSION
Oral Session #10: Paleoecology. Presiding: S. Hotchkiss.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas J.

A high-resolution record of late Holocene surface-moisture changes from a Michigan raised bog.

Booth, Robert¹, Jackson, Stephen¹, ¹

ABSTRACT- Testate amoebae are sensitive indicators of surface-moisture conditions in Sphagnum-dominated wetlands. We analyzed testate amoeba assemblages at 1-cm intervals in a sediment core from Minden Bog, an ombrotrophic peatland in northeast lower Michigan. Transfer functions based on modern species and environmental data were used to infer surface-moisture changes during the last 2800 years. Our results indicate that surface moisture varied on centennial and sub-centennial scales. Inferred surface-moisture changes during the last 100 years show strong correspondence with the Palmer Drought Severity Index, validating our application. Very wet conditions characterized the bog from 1900 to 800 cal yr BP, and generally drier conditions occurred from 2800-1900 and 800-0 BP. The driest conditions occurred between 150-100 BP, a period of major wildland fires in the region. Inferred hydrological variation at Minden Bog between 2800 and 1400 BP closely tracks independently documented water-level fluctuations in Lake Michigan. Although lake-level dropped after 1400 BP, Minden Bog remained wet until 800 BP. The Minden Bog record also appears to mirror records from the Great Plains. The diatom-inferred salinity record of Moon Lake, ND records a predominantly dry to predominantly wet climatic shift at about 800 BP. Minden Bog records a climatic shift in the opposite direction (wet to dry) at this time, suggesting spatially complex climate patterns.

KEY WORDS: testate amoebae, paleoecology, paleoclimate, Great Lakes