Changing palynological methods and their role in three successive interpretations of the late‐glacial environments at Bucyrus Bog, Ohio, USA

The pollen stratigraphy of Bucyrus Bog records the major shifts in the spruce ecotone of the mid‐western North American late‐glacial. The site has been studied three times: in 1930 by Paul Sears, in 1958 by Johannes Iversen, and in 1986–88 by my self. This paper examines these data sets from a historical perspective. The pollen record is basically consistent; all investigators interpret it to show the classic late‐glacial warming plus a subsequent, more controversial climate reversal. Sears saw a progressive shift from cold/moist to warm/ dry climate, with a moisture reversal near the top of the record. Iversen and I both correlate the record with the European Late‐Glacial climatic sequence, including an AUerød/Younger Dryas reversal. Iversen's interpretation depends on exclusion of thermophilous deciduous pollen taxa, placing the cold reversal during the spruce decline. I include the deciduous taxa, placing the cold reversal at the time of a spruce recurrence above the expansion of deciduous types. All interpretations are strongly influenced by current technology and prevailing thinking at the time of the investigation.