Late-glacial and Holocene 14C/12C ratios of atmospheric CO2 vary in magnitude from a few per mil for annual/decadal pertubations to more than 10% for events lasting millennia. A data set illuminating 10- to 104-yr variability refines our understanding of oceanic (climatic) versus geomagnetic or solar forcing of atmospheric 14C/12C ratios. Most of the variance in the Holocene atmospheric 14C/12C record can be attributed to the geomagnetic (millennia time scale) and solar (century time scale) influence on the flux of primary cosmic rays entering the atmosphere. Attributing the observed atmospheric 14C/12C changes to climate alone leads to ocean circulation and/or global wind speed changes incompatible with proxy records. Climate-(ocean-)related 14C redistribution between carbon reservoirs, while evidently playing a minor role during the Holocene, may have perturbed atmospheric 14C/12C ratios measurably during the late-glacial Younger Dryas event. First-order corrections to the radiocarbon time scale (12,000–30,000 14C yr B.P.) are calculated from adjusted lake-sediment and tree-ring records and from geomagnetically defined model 14C histories. Paleosunspot numbers (100–9700 cal yr B.P.) are derived from the relationship of model 14C production rates to sunspot observations. The spectral interpretation of the 14C/12C atmospheric record favors higher than average solar activity levels for the next century. Minimal evidence was found for a sun-weather relationship.

The radiocarbon ages of dendrochronologically-dated wood samples, each covering 10 years, are now available for the cal AD 1950–6000 BC age range. The decadal calibration curve constructed from these data comprises 1) the previously published AD 1950–2500 BC portion (Stuiver & Becker 1986), to which minor 14C age corrections were applied, and 2) the new 2500–6000 BC extension.

Radiocarbon calibration data derived from German oak chronologies, ranging back to 7200 BC, have been published in the previous Calibration Issue (Stuiver & Kra 1986). In recent years, the German oak chronology has been extended to 7938 BC (Becker, this issue). For earlier intervals, tree-ring chronologies must be based on pine, because oak re-emigrated to central Europe at the Preboreal/Boreal transition, at about 8000 BC. We have established a 1784-yr pine chronology centered in the Preboreal, and have linked it tentatively to the absolutely dated oak master. We present here calibration data based on this link, for the age range, 7145–9439 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.