Absolute dating of the late-glacial period in Switzerland using annually laminated sediments

Abstract

Results of a high-resolution late-glacial AMS 14C chronology from Rotsee, central Switzerland, have given evidence that the atmospheric radiocarbon concentration was not constant between 13,000 and 9500 yr B.P. This resulted in three marked phases of constant radiocarbon age: at 12,700, at 10,000, and at 9500 yr B.P. New results of a late-glacial varve chronology from Soppensee, central Switzerland, suggest that the younger two phases of constant 14C age each had a duration of ca. 400 calendar years. The length of the late-glacial chronozones has been calculated on the basis of these replicate varve counts and a comparison with their estimated duration in radiocarbon years shows that the estimated duration of the chronozones Bölling (ca. 800 calendar yr vs 1000 14C yr) and Younger Dryas (ca. 900 calendar yr vs 1000 14C yr) agree with the expected time span, whereas the estimated duration of the Alleröd chronozone (ca. 400 calendar yr vs 1000 14C yr) is substantially shorter than expected. Furthermore, a tentative comparison of varve ages and 14C ages suggests that the varve chronology is more than 1000 yr offset toward older ages from the radiocarbon chronology during the late-glacial period.