QUATERNARY RESEARCH 32, 205-212 (1989) Radiocarbon Dating of Pollen by Accelerator Mass Spectrometry THOMAS A. BROWN,’ D. ERLE NELSON, ROLF W. MATHEWES,* JOHN S. VOGEL, AND JOHN R. SOUTHON Department of Archaeology and *Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A IS6 Received March 9, 1989 Radiocarbon dating of bulk sediments has been the standard method for establishing chronolo- gies in the studies of lake sediment cores which have contributed significantly to our knowledge of late Quatemary paleo-environments. These bulk sediment dates are presumed to be direct age- indicators for the specimens (e.g., pollen or macrofossils) which are actually being studied. How- ever, several recent studies have reinforced long-standing apprehensions concerning this presump- tion. In this study. we demonstrate for the first time the radiocarbon dating of pollen concentrate samples by accelerator mass spectrometry. The dates obtained by this method should provide more reliable radiocarbon chronologies for paleo-environmental studies than have been obtainable by bulk sediment dating. 8 1989 University of Washington. INTRODUCTION Reconstructing paleo-environments and understanding the mechanisms governing climatic change have been the goals of con- siderable research (e.g., Duplessy et al., 1986; Mott et al., 1986; Heusser and Ra- bassa, 1987; Broecker et al., 1988; CO- MAP, 1988). The establishment of accurate chronologies for the proxy climate records used in these studies is of crucial impor- tance, especially in attempting to determine the timing and geographical extent of rela- tively short-duration events such as re- gional deglaciation, the Younger Dryas cooling, or tree species migrations. In stud- ies of continental paleo-environments, the records are predominantly based on pollen or fossil plant material in lake sediment cores, and the chronologies for these cores are usually obtained by radiocarbon mea- surements on the total organic carbon of the bulk sediments. This is less than ideal because there are numerous processes and sources of contaminating carbon which can cause significant and varying differences ’ Present address: Nuclear Physics Laboratory GL- 10, and Geophysics Program AK-50, University of Washington, Seattle, WA 98195. between the radiocarbon content of the bulk sediment and that of the proxy climate indicator (Davis, 1974; Mathewes and Westgate, 1980; Sutherland, 1980; Andree et al., 1986; Olsson, 1986; MacDonald et al., 1987; Lowe et al., 1988; Vogel et al., in press (a)). Such differences can make es- tablishing trustworthy correlations between records difficult; for example, Clayton and Moran (1982) have proposed that deglacia- tion of middle North America can best be understood by ignoring the available bulk sediment dates and using only those ob- tained from wood samples found in unam- biguous stratigraphic settings. We have developed a sample preparation method which concentrates pollen from bulk sediments while removing carbon- containing contaminants, and have ex- ploited the small sample capabilities of ac- celerator mass spectrometry (AMS) (Nel- son et al., 1986; Vogel et al., 1987, in press (b)) in radiocarbon dating these pollen con- centrates. The method is an extension of sample pretreatments normally used in paly- nological studies and typical sediment samples produce sufficient pollen concen- trate to allow routine use of the method with minimal effort (unlike macrofossil dat- 20.5 0033-5894189 $3.00 Copyright Q 1989 by the University of Washingron. All nghts of reproduction in any form reserved.