Radiocarbon ages of dendrochronologically-dated wood spanning the last 4500 years were determined at both the Seattle and Belfast laboratories. The combined results are reported in this issue of radiocarbon in two papers, with this paper covering the AD 1950—500 BC interval, and the twin (Pearson & Stuiver, 1986) covering the 500 BC–2500 BC interval.

This paper is a twin paper to that of Stuiver and Pearson (1986) which covers the time period ad 1950–500 bc. The combined radiocarbon ages of dendrochronologically dated wood presented in this paper covers the time period 500–2500 bc.

The radiocarbon ages of dendrochronologically dated wood samples, each covering 10 years, are reported back to 2500 yr BC. The decadal calibration curve constructed from these data is an extension of the curve previously given for the AD interval (Stuiver, 1982). A major difference with the previous work, however, is the assessment of the error in the radiocarbon age determination. Whereas previously this error was only based on the Poisson counting statistics of the accumulated number of counts for the sample and standards, the current calibration error is based on an estimate of the reproducibility in the radiocarbon activity determination. As a consequence, the uncertainty in the current calibration curve is, on average, 1.6 times that of the AD curve previously given.

High-precision measurement of dendrochronologically dated Irish oak at bi-decade/decade intervals has continued in the Belfast laboratory, extending the 14C data base from ca AD 1840 to 5210 BC. The dendrochronology is now considered absolute (see Belfast dendrochronology this conference) (Brown et al, 1986) and a continuous detailed curve is presented, showing the natural variations in the atmospheric concentration of 14C over >7000 years. Each data point has a precision of <2.5., and some 4500 years have now been compared with Seattle, giving excellent agreement. Discussion of this data base and the justification of the claimed accuracy is given together with a comparison of other chronologies. Some of the advantages and limitations of the above are discussed.

Precision 14C analyses have been performed on samples comprising 1 to 4 annual rings from the south-central European dendrochronologic sequence of sub-fossil oak wood covering the period 1930 to 3100 bc. Apart from a major deviation in the 29th century bc, the 14C fluctuations have amplitudes of ca 10‰ and a possible periodicity of 90 years. A 14C peak at 2190 bc has a rise- and decay-time of <20 years indicating rather abrupt changes in the production rate of 14C. The 14C calibration curve derived from these data can be used for precise dating of the Early Bronze Age in the Near East.

This paper contains 14C results obtained by the special high-precision proportional gas counter, designed by Tans and Mook (1978), on tree rings from the South German oak chronologies: Donau 7, 3, 10, and 12, originating from the Danube River basin (48° 24’ N, 10° 5’ E).

New results of radiocarbon dating of ca 100 decadal bristlecone pine samples from 6554 BC to 6084 BC and from 5820 to 5350 BC are presented. Using 3 new 2.5L counters filled to ca 3atm with carbon dioxide, high-precision dating has been performed by this laboratory for more than two years. Demonstration of the precision and accuracy of these counters is presented using ±2‰ measurements from the Spörer minimum period. For the older samples, ±3‰ measurements were made using ca 12-day counting times. Results are presented both as C age bp vs dendro-year BC, particularly for calibration purposes, and as Δ14C vs time.

14C calibration curves derived from South German oak tree-ring series are presented. They cover the interval between 4400 and 7200 BC complementing existing data sets and extending them to older periods. The atmospheric 14C level before 6200 BC no longer follows the long-term sinusoidal trend fitted to the bristlecone data. This observation is supported by a tentative match of the Main 9 series.

Holocene tree-ring chronologies have been established for south-central Europe covering the past 11,000 years. The Hohenheim absolute oak chronology extends to 4089 bc. The C-calibrated mid-Holocene floating oak master covers a 3181-year period from ca 4045 to 7225 bc. The earliest well-replicated floating oak master (estimated calendar age 7215 to 7825 bc) extends the European oak dendrochronology back to Boreal times.

Further extension of the Holocene dendrochronology has been achieved by subfossil oak and pine trees from the Rhine, Main, and Danube Rivers. A 774-year floating series of Preboreal pine has been established. 14C ages range (from younger to older end) from 9200 to 9800 BP. Within this series a major atmospheric 14C variation is indicated, resulting in nearly constant 14C ages (9600 BP) over a period of 370 tree-rings.

The European oak and pine tree-ring chronologies cover without major gaps the entire Holocene epoch. Based on the length of the dendro-records, an approximate solar year age of 11,280 years is calculated for the Holocene/Pleistocene boundary.

The Preboreal pine forests along the rivers were replaced by mixed oak forests between 9200 and 8800 BP. By linking the earliest oak masters and the Preboreal pine series, the European dendrochronology can be extended up to the end of Late Glacial times.

With the recent establishment of an unbroken West European tree-ring sequence spanning the past 7272 years (Pilcher et al, 1984) the calibration of the 14C time scale was advanced considerably. It is now possible to use this chronology as an independent cross-check on the 8681-year US Bristlecone Pine series (Ferguson & Graybill, 1983). There also are opportunities for 14C matching (wiggle matching) between the older portion of the Bristlecone Pine series and floating (not tied to the present) parts of the South German Oak sequence. Linick, Suess and Becker (1985) used this approach in matching the earliest part of the Bristlecone Pine series with the Donau 6 Main 4/11 (Becker, 1983) series and thus established a D6M4/11 “zero” point (tree-ring no. 1) of 7215 bc.

Calibration curves spanning several millennia are now available in this special issue of Radiocarbon. These curves, nearly all derived from the 14C age determinations of wood samples, are to be used for the age conversion of samples that were formed through use of atmospheric CO2. When samples are formed in reservoirs (eg, lakes and oceans) that differ in specific 14C content from the atmosphere, an age adjustment is needed because a conventional 14C age, although taking into account 14C (and 13C) fractionation, does not correct for the difference in specific 14C activity (Stuiver & Polach, 1977). The 14C ages of samples grown in these environments are too old, and a reservoir age correction has to be applied. This phenomenon has been referred to as the reservoir effect (Stuiver & Polach, 1977).

The calibration curves and tables given in this issue of RADIOCARBON form a data base ideally suited for a computerized operation. The program listed below converts a radiocarbon age and its age error os (one standard deviation) into calibrated ages (intercepts with the calibration curve), and ranges of calibrated ages that correspond to the age error. The standard deviation oC in the calibration curve is taken into account using (see Stuiver and Pearson, this issue, for details).