The age calibration program, CALIB (Stuiver & Reimer 1986), first made available in 1986 and subsequently modified in 1987 (revision 2.0 and 2.1), has been amended anew. The 1993 program (revision 3.0) incorporates further refinements and a new calibration data set covering nearly 22,000 cal yr (≈18,400 14C yr). The new data, and corrections to the previously used data set, derive from a 6-yr (1986–1992) time-scale calibration effort of several laboratories.

Count rates, representing the rate of 14C decay, are the basic data obtained in a 14C laboratory. The conversion of this information into an age or geochemical parameters appears a simple matter at first. However, the path between counting and suitable 14C data reporting (table 1) causes headaches to many. Minor deflections in pathway, depending on personal interpretations, are possible and give end results that are not always useful for inter-laboratory comparisons. This discussion is an attempt to identify some of these problems and to recommend certain procedures by which reporting ambiguities can be avoided.

ABSTRACT. The focus of this paper is the conversion of radiocarbon ages to calibrated (cal) ages for the interval 24,000-0 cal BP (Before Present, 0 cal BP = AD 1950), based upon a sample set of dendrochronologically dated tree rings, uranium-thorium dated corals, and varve-counted marine sediment. The 14C age-cal age information, produced by many laboratories, is converted to 14C profiles and calibration curves, for the atmosphere as well as the oceans. We discuss offsets in measured 14C ages and the errors therein, regional 14C age differences, tree-coral 14C age comparisons and the time dependence of marine reservoir ages, and evaluate decadal vs. single-year 14C results. Changes in oceanic deepwater circulation, especially for the 16,000-11,000 cal BP interval, are reflected in the A14C values of INTCAL98.

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INTRODUCTIONThe detailed radiocarbon age vs, calibrated (cal) age studies of tree rings reported in this Calibration Issue provide a unique data set for precise 14C age calibration of materials formed in isotopic equilibrium with atmospheric CO2. The situation is more complex for organisms formed in other reservoirs, such as lakes and oceans. Here the initial specific 14C activity may differ from that of the contemporaneous atmosphere. The measured remaining 14C activity of samples formed in such reservoirs not only reflects 14C decay (related to sample age) but also the reservoir '4C activity. As the measured sample 14C activity figures into the calculation of a conventional 14C age (Stuiver & Polach 1977), apparent 14C age differences occur when contemporaneously grown samples of different reservoirs are dated.A correction for the apparent age anomaly is possible when the reservoir-atmosphere offset in specific 14C activity is known. The offset (e.g.,14C age of marine sample -14C age of atmospheric sample) is expressed as a reservoir 14C age, R(t), which need not be constant with time. When constant, however, the reservoir sample 14C age, A, can be reconciled with the atmospheric one by deducting R(t) from A. Similar reservoir age corrections would be possible for a variable R(t), but complications arise because information on R time dependency usually is lacking. However, R(t) can be accounted for in the world oceans by using a marine calibration curve derived from carbon reservoir modeling (Stuiver, Pearson & Braziunas 1986). In these calculations, atmospheric 14C change is attributed to solar-and geomagnetic-induced 14C production change. Climate-induced changes in global carbon reservoirs, which may repartition 14C among reservoirs, are not accounted for in these calculations.Measuring a marine calibration curve is complicated because most marine samples lack the continuity and fine structure of tree rings. The 234U/23°Th dating of corals (Bard et al. 1993) provides a good cal age equivalent, but measuring errors in the 234U/230Th ratio and 14C accelerator mass spectrometry (AMS) determinations are such that the (bi)decadal chronological detail achieved for tree rings is not possible. Such detail, however, can be realized by calculating the response of the world oceans to tree-ring derived atmospheric 14C changes.The long-term trend of the 14C age vs. cal age curve for the world oceans parallels that of the atmosphere. Short-term (century) variations, however, are smoothed in the oceans. Thus, whereas a constant, R, could be used for long-term variations, the shorter-term variations cannot be accounted for in this manner. Use of constant, R, and the atmospheric calibration curve assumes that the features of the marine and atmospheric curves are identical. The consequences of the constant R approach are obvious when the cal ages of a marine and atmospheric sample with identical (reservoir-corrected) 14C age + standard deviation are evaluated. Calibration of both vs. the atmospheric curve yields identical re...

Single-year and decadal radiocarbon tree-ring ages are tabulated and discussed in terms of 14C age calibration. The single-year data form the basis of a detailed 14C age calibration curve for the cal ad 1510–1954 interval (“cal” denotes calibrated). The Seattle decadal data set (back to 11,617 cal BP, with 0 BP = ad 1950) is a component of the integrated decadal INTCAL98 14C age curve (Stuiver et al. 1998). Atmospheric 14C ages can be transformed into 14C ages of the global ocean using a carbon reservoir model. INTCAL98 14C ages, used for these calculations, yield global ocean 14C ages differing slightly from previously published ones (Stuiver and Braziunas 1993b). We include discussions of offsets, error multipliers, regional 14C age differences and marine 14C age response to oceanic and atmospheric forcing.

ABSTRACT. New radiocarbon calibration curves, IntCal04 and Marine04, have been constructed and internationally ratified to replace the terrestrial and marine components of IntCal98. The new calibration data sets extend an additional 2000 yr, from 0-26 cal kyr BP (Before Present, 0 cal BP = AD 1950), and provide much higher resolution, greater precision, and more detailed structure than IntCal98. For the Marine04 curve, dendrochronologically-dated tree-ring samples, converted with a box diffusion model to marine mixed-layer ages, cover the period from 0-10.5 cal kyr BP. Beyond 10.5 cal kyr BP, high-resolution marine data become available from foraminifera in varved sediments and U/Th-dated corals. The marine records are corrected with site-specific 14 C reservoir age information to provide a single global marine mixed-layer calibration from 10.5-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a random walk model, which takes into account the uncertainty in both the calendar age and the 14 C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed here. The tree-ring data sets, sources of uncertainty, and regional offsets are presented in detail in a companion paper by Reimer et al. (this issue).