DGESL : Publications : Abstracts : Overpeck et al. 1985

Quantitative Interpretation of Fossil Pollen Spectra: Dissimilarity Coefficients and the Method of Modern Analogs

Overpeck, J.T., T. Webb III, I.C. Prentice

1985 Quaternary Research 23: 87-108

ABSTRACT

Dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples. How 8 coefficients responded to differences among modern pollen samples from E North America was tested. These coefficients represent 3 different classes: 1) unweighted coefficients that are most strongly influenced by large-valued pollen types, 2) equal-weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types, and 3) signal-to-noise coefficients that are intermediate in their weighting of pollen types. The studies with modern pollen allowed definition of critical values for each coefficient, which when not exceeded, indicate that 2 pollen samples originate from the same vegetation region. Dissimilarity coefficients were used to compare modern and fossil pollen samples, and modern samples so similar to fossil samples were found that most of 3 late Quaternary pollen diagrams could be 'modeled' by substituting modern samples for fossil samples. When the coefficients indicated that the fossil spectra had no modern analogs, then the reconstructed diagrams did not match all aspects of the originals. No modern analogs existed for samples from before 9300yr BP at Kirchner Marsh, Minnesota, and from before 11 000yr BP at Wintergreen Lake, Michigan, but modern analogs existed for almost all Holocene samples from these 2 sites and also Brandreth Bog, New York.