and BERND BECKER Botanisches Institut, Universitat Stuttgart-Hohenheim 7000 Stuttgart 70, West Germany

Transcription

1 [RADIOCARBON, VOL 27, No., 985, P 20-32] LA JOLLA MEASUREMENTS OF RADIOCARBON IN SOUTH GERMAN OAK TREE-RING CHRONOLOGIES T W LINICK*, H E SUESS Mt Soledad Radiocarbon Laboratory, University of California, San Diego, La Jolla, California and BERND BECKER Botanisches Institut, Universitat Stuttgart-Hohenheim 7000 Stuttgart 70, West Germany ABSTRACT. Radiocarbon measurements made by the La Jolla laboratory on tree-ring samples from South German oak chronologies are presented. Several previously separate treering series have been reduced to one absolutely dendro-dated chronology spanning the period from 4066 BC to the present and one still-floating chronology which spans the approximate period 7225 to 425 BC. Previous estimates of the dendro-years made by the authors are compared with the dendro-years now assigned. From 974 through 982, the 4C contents of 575 European oak treering samples were determined at the La Jolla laboratory. The samples came from tree-ring chronologies established by one of us (BB) from sub-fossil oak cross sections collected from South German river deposits. The '4C measurements on these samples provided a substantial basis for a preliminary estimation of the absolute ages of these then-floating Holocene oak tree-ring chronologies. This was accomplished by comparing their 4C variations with those obtained for the absolutely dendro-dated bristlecone-pine chronology using wiggle-matching methods (Kruse et al, 980). During the past two years, several of the original Hohenheim Holocene oak series have been significantly enlarged and successively linked together into longer units. In cooperation with M G L Baillie and J Pilcher, Paleoecology Centre, Queen's University, Belfast, Northern Ireland, and B Schmidt, Dendrochronology Laboratory, University of Cologne, West Germany, it was possible to close the long-standing gap in the Hohenheim oak chronology. After correction by 7 years of a tentative, but incorrect, link of the South German series starting at 500 BC (Becker, 983) and a successful cross-match between the Northern Irish, North German, and South German series from 2000 BC to AD 500 (Pilcher et al, in press), the absolutely dendro-dated Hohenheim oak chronology today extends continuously from the present back to 4066 BC. Suess (978) published 4C data for the La Jolla analyses of the floating Hohenheim oak series Donau 7/9/2, Main 5, Donau 3/0, and Zug- Sumpf. In 980 the authors published estimated absolute dendro-years of these series derived from computer-matching of their 4C variations with those in the La Jolla bristlecone-pine absolute chronology (Kruse et al, 980). Because of the recently established tree-ring-width matches of these individual series into a sinle continuous absolutely dendro-dated sequence, the accuracy of the 4C wiggle-matching method can be checked. As listed in Table, the calibrated zero points (years of oldest rings) of the *Present address: Laboratory of Isotope Geochemistry, Department of Geosciences, University of Arizona, Tucson, Arizona

2 La Jolla'4C Dates in South German Oak Tree- Chronologies 2 four previously floating series differ from their absolute dendro-years by less than 0 years, with a range of 3 to 7 years difference. This fact demonstrates once again the validity of absolute radiometric age determinations by matching short-term 4C variations in floating tree-ring series with those in absolutely dated tree-ring chronologies. Progress has also been achieved in linking together the Hohenheim oak series older than 400 BC. The floating chronologies Donau 6-Main 4/, Main 6/ 3, Donau, and Donau 8 have recently been cross-matched (using relative ring widths) into a continuous 382-year series. These series were initially calibrated individually by wiggle-matching with the bristlecone-pine chronology data. The zero point years estimated for the Donau 8 and Main 63 series were 4870 BC and 6457 BC, respectively. On the basis of an apparent overlap of only ca 50 years of the youngest end of the Donau 6-Main 4/ series and the oldest end of the ' C-dated bristleconepine series, a zero point of 72.5 BC was assigned to the Donau 6-Main 4 series, which spans over 800 years. After the successful connection of these three series (according to ring widths) into a single continuous floating series, the previous wiggle-matching calibrations can be checked. The comparison of previous and new zero points is given in Table 2. If the single continuous floating series is assigned the zero point of the oldest series, Donau 6-Main 4/, of 725 BC, the revised zero points of the Main 6/3 and Donau 8 series differ by less than 20 years from their previous values. Recent measurements made by Minze Stuiver, Quaternary Isotope Laboratory, University of Washington, Seattle, and Bernd Kromer, Institut fur Umweltphysik, Universitat Heidelberg, West Germany, on samples from these older Hohenheim series confirm the La Jolla calibrations; details of their calibrations will be presented by Stuiver and Kromer at the 985 radiocarbon conference in Trondheim, Norway. The zero point of 725 BC for the Donau 6-Main 4/-Main 6/3-Donau 8 series can be assumed to be correct to within 20 years. Data for many of the samples listed here were presented in a preliminary publication (Suess,978). The data for these samples have been recalculated using 95% of the activity of the original NBS oxalic acid standard as the reference; previously, the decay-corrected activity of mid-to late-9th century Douglas fir tree rings had been used as the reference standard at the La Jolla laboratory. Some of the data for samples from the Donau 6- Main 4 series, which appears to span the period 7225 to 6375 BC, were published by Bruns et al (983). The La Jolla data for the Hohenheim oak series are presented in two tables, with samples ordered from oldest to youngest. The data for the unified floating series from ca 7225 to 425 BC are presented in Table 3, while those for the absolutely dendro-dated series covering the period from 4066 BC to AD 250 are given in Table 4. In these two tables, the columns give, from left to right, () the ring number, (2) the midpoint dendro-year (AD +, BC -, assigned by wiggle-matching or by absolute dendro-dating), (3) the number of tree rings in the sample, (4) the laboratory number (LJ - ), (5) the b' 3C (%o, PDB) measured on a recombusted aliquot of the acetylene counting gas, (6) the conventional 4C age (years BP, tl/2 = 5568 years) and

3 22 T W Linick, H E Suess, and Bernd Becker its one standard deviation statistical uncertainty, and (7) the (%o, decay-corrected, based on the dendro-year, using t,/2 = 5730 years) and its one standard deviation statistical uncertainty. ACKNOWLEDGMENTS The tree-ring studies carried out in Hohenheim were financially supported by the Deutsche Forschungsgemeinschaft. Operations of the Mt Soledad Radiocarbon Laboratory, La Jolla, were financed until 980 through a grant from the US National Science Foundation, Atmospheric Science Division. However, support from the National Science Foundation was terminated at that time; this has led to a most regrettable delay in publication of these data, as well as final data from 4C dating of the bristleconepine chronology (including data for some samples measured after the Suess (978) publication). Wood samples from the bristlecone-pine chronology were furnished to the La,Jolla laboratory by C W Ferguson, Laboratory of Tree- Research, University of Arizona. We greatly appreciate the support from the Alexander von Humboldt Foundation, West Germany, that provided the possibility for the close cooperation between the European and American investigators and thus enabled completion of this manuscript. 4C TABLE Comparison between 4C-calibrated zero point years of the previously floating Hohenheim Neolithic and Bronze age oak series and zero points based on linkage of series into absolutely dendro-dated master chronology Name of floating series Donau 7/9/2 Main 5 Donau 3/0 Zug-Sumpf 4C-calibrated zero point zero point (yr) Bc 3262 BC 287 BC 238 BC BC 3259 BC 2875 BC 24 BC TABLE 2 Comparison between 4C-calibrated zero points of the floating Hohenheim oak series older than 400 BC and their zero points after linkage of the series into a single continuous floating chronology Name of floating series Donau 6-Main 4/ Main 6/3 Donau 8 4C-calibrated zero point BC 6457 BC 4870 BC point after linkage into one series starting at 725 BC BC 6440 BC 485 BC

4 La Jolla 4C Dates in South German Oak Tree- Chronologies 23 no. Year rings no. TABLE 3 Floating series, ca 7225 to 425 BC J ± C age 4C

5 24 T W Linick, HE Suess, and Bernd Becker TABLE 3 (continued) no. Year rings no. age 4C ± 6.9

6 La Jolla '4C Dates in South German Oak Tree- Chronologies 25 TABLE 3 (continued) no. Year rings no. age ± 4.

7 26 T W Linick, HE Suess, and Bernd Becker TABLE 3 (continued) no. Year rings no. age l l l l l l

8 La- Jolla'4C Dates in South German Oak Tree- Chronologies 27 TABLE 3 (continued) no. Year rings no. age l TABI.E 4 Absolutely dendro-dated series, 4066 BC to Al) 250 no. Year rings no. age 4C l l l ± 6.0

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10 La Jolla "C Dates in South German Oak Tree- Chronologies 29 TABI.E 4 (Continued) no. Year rings J no.. 4C l l l l l l l l l

11 30 T W Linick, H E Suess, and Bernd Becker TABLE. 4 (continued) no. Year rings no. 4C I l l () l l l l l 95 l 4 ± l l l l l l l l _ ±5.2

12 LaJolla '4C Dates in South German Oak Tree- Chronologies 3 TABLE 4 (continued) 4 no. Year rings J no. age a l l l ' '

13 32 T W Linick, HE Suess, and Bernd Becker TABLE 4 (continued) no. Year rings LJ no C age 4C I REFERENCES Becker, Bernd, 983, The long-term radiocarbon trend of the absolute oak tree-ring chronology, 2800 to 800 BC, in Stuiver, Minze and Kra, R S, eds, International 4C conf, th, Proc: Radiocarbon, v 25, no. 2, p Bruns, M, Rhein, M, Linick, T W, and Suess, H E, 983, The atmospheric 4C level in the 7th millenium BC, in Mook, W G and Waterbolk, H T, eds,4c and archeology: PACT, Strasbourg, v 8, p Kruse, H H, Linick, T W, Suess, H E, and Becker, Bernd, 980, Computer-matched radiocarbon dates of floating tree-ring series, in Stuiver, Minze and Kra, R S, 4C eds, International conf, 0th, Proc: Radiocarbon, v 22, no. 2, p Pilcher, J R, Baillie, MG L, Schmidt, B, and Becker, B, 984, A 7272-year European tree-ring chronology: Nature, v 32, p Suess, H E, 978, La Jolla measurements of radiocarbon in tree-ring dated wood: Radiocarbon, v 20, p -8.