Patterns of variation in late-glacial pollen stratigraphy along a northwest-southeast transect through Switzerland—A numerical analysis

Abstract

Palynological data from seven late-glacial sites on a transect from the Swiss Plateau, through the North and Central Alps to the South Alps are analysed numerically. Constrained classification procedures were used to derive local pollen-assemblage zones for each site. Detrended correspondence analysis was used to compare pollen-stratigraphical similarities and differences within and between sites and to estimate the amount of palynological change at each site. Canonical correspondence analysis was used to display graphically patterns of variation between local zones within the sites and between the seven sites, and to partition the total palynological variance into within-site temporal variation and between-site spatial variation. The numerical results suggest that no two sites have identical late-glacial pollen stratigraphies, that the South Alps site has a very different pollen stratigraphy compared with the other sites, that the major spatial patterns of variation correspond to site location, and thus that there was considerable variation in late-glacial pollen rain along the transect, just as there is today. The total palynological variance is partitioned into 73% temporal variance, 13.2% spatial variance and 13.8% unexplained variance. The Younger Dryas ‘event’ is poorly reflected in the South Alps but is well reflected as a palynological revertence towards pre-Allerød assemblages at mid- and high-elevation sites in the North and Central Alps. It is also well reflected as changes in pollen composition at one site on the Swiss Plateau, but is poorly reflected at a nearby site on the Swiss Plateau.