Bernd Becker

High-precision decadal calibration of the radiocarbon time scale, AD 1950-2500 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.

Climatic, solar, oceanic, and geomagnetic influences on late-glacial and holocene atmospheric 14C12C change

Late-glacial and Holocene 14C12C 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 14C12C ratios. Most of the variance in the Holocene atmospheric 14C12C 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 14C12C 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 14C12C 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 14C12C atmospheric record favors higher than average solar activity levels for the next century. Minimal evidence was found for a sun-weather relationship.

German oak and pine (super 14) C calibration, 7200-9439 BC.

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.

Radiocarbon age calibration back to 13,300 years BP and the (super 14?C age matching of the German Oak and US bristlecone pine chronologies.

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 14 C 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 14 C 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.

An 11,000-year German oak and pine dendrochronology for radiocarbon calibration.

Sequences of dendrodated tree rings provide ideal sources for radiocarbon calibration. The wood structure of trees consists of continuous series of annual growth layers, the carbon content of which can be 14 C-dated and calibrated to calendar yr. The cellulose and lignin of trees deposited in river gravels or peat-bog sediments below the water table are often very well preserved, even after several millennia. Such tree-trunk deposits are well protected from contamination by younger or older organic materials. Further, the physical and chemical structure of wood allows a strong chemical pretreatment of samples for 14 C analysis.

Radiocarbon calibration data for the 6th to the 8th millennia BC.

MINZE STUIVER* , ABSTRACT. 14C calibration curves derived from South German oak tree-ring series are pre sented. 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.

Corrected Calibration of the Radiocarbon Time Scale, 3904-3203 Cal BC

Since our publication of the high-precision calibration curve for the larger part of the 4th millennium BC (de Jong, Becker & Mook, 1986), we found that the dendrochronologic scale (cal BC) needs a correction of 26 years. Instead of using the zero-point of the Niederwill chronology (4039 BC) which was floating at the time, our dendrochronologic scale was erroneously based on the zero-point of the Hohenheim master chronology, which, in its 1986 stage, extended to 4065 BC. By this correction of 26 years there is now good agreement with the calibration curve of Pearson et at (1986), as shown in Figure 1. The definitive calibration curve is shown in Figure 2. Table 1 contains the revised data.

Tree-rings, absolute chronology and climatic change

In the Hohenheim tree-ring laboratory, two long tree-ring chronologies have been built, spanning the past 11 600 years. This is the worlds longest continuous tree-ring calendar. It has become the backbone of the calibration of the radiocarbon time scale, offering absolute and accurate dates for archaeology, vegetation history and paleoclimate studies. 14 C analyses of the tree-ring chronologies provide insight into the process controlling the production of cosmogenic nuclides, i.e. mainly the geomagnetic dipole moment and solar variability. They also set geochemical constraints to variations in the carbon cycle during a major climatic excursion.