Revisions and extension of the Hohenheim oak and pine chronologies: New evidence about the timing of the Younger Dryas/Preboreal transition

Oak and pine samples housed at the Institute of Botany, University of Hohen heim, are the backbone of the early Holocene part of the radiocarbon calibr ation curve, published in 1993 (Becker 1993; Kromer and Becker 1993; Stuive r and Pecker 1993; Vogel et al. 1993). Since then the chronologies have bee n revised. The revisions include 1) the discovery of 41 missing years in th e oak chronology and 2) a shift of 54 yr for the oldest part back into the past. The oak chronology was also extended with new samples as far back as 10,429 sp (8480 Be). In addition, the formerly tentatively dated pine chron ology (Becker 1993) has been rebuilt and shifted to an earlier date. It is now positioned by C-14 matching at 11,871-9900 sp (9922-7951 BC) with an un certainty of +/-20 yr (Kromer and Spurk 1998). With these new chronologies the 14C calibration curve can now be corrected, eliminating the discrepancy in the dating of the Younger Dryas/Preboreal transition between the proxy data of the GRIP and GISP ice cores (Johnsen et al. 1992; Taylor et al. 199 3), the varve chronology of Lake Gosciaz (Goslar et al. 1995) and the pine chronology (Becker, Kromer and Trimborn 1991).