The present state of dendrochronology and tree ring calibration of the Late Glacial, and the inglorious end of the "Achterberg-wiggle"

Abstract

In our paper on Late Glacial and Late Upper Palaeolithic chronology in the Netherlands and adjacent areas we also looked for indications of the existence of wiggles in Late Glacial peat deposits with multiple radiocarbon dates (Lanting & Van der Plicht, 1995/96: 79- 83). In a 1.8 m thick peat deposit near Achterberg, studied by the Rijks Geologische Dienst and provided with 17 14C-dates (ibid.: 81, Table 2 and Fig. 7) such an indication seemed to be present. During the earlier part of the Allerød period six samples in sequence suggested a sudden change in atmospheric 14C-content: first a strong increase resulting in 14C-ages dropping from 12,050±90 BP (sample 12) to 11,550±80 BP (sample 11) to 10,740±60 BP (sample 10), next a decrease resulting in 14C-ages of 11,070±60 BP (sample 17), 11,260±60 BP (sample 16) and 11,540±70 BP (sample 9). The Achterberg samples received thorough AAA pre-treatment. Carbon percentages and δ13C values were calculated for all samples. No indications for contamination were found. Of samples 9 and 10 the alkali soluble fractions were also dated: 10,870±90, resp. 10,520±90 BP. Clearly some downward transport of younger humic substances had taken place, but that was to be expected. Although a wiggle of c. 1000 radiocarbon years was and is highly unlikely, and no counterparts were known in the then available calibration curve (Kromer & Spark, 1998), the existence could not be fully excluded. And an ‘Achterberg’ wiggle seemed to explain a number of aberrant 14C-age determinations of archaeological material