The basic chronology of Inca imperial expansion in Andean South America derives from historical accounts from the Spanish Colonial era, but several issues with this traditional chronology have arisen in recent decades. Advances in radiocarbon dating and calibration now give us some ability to refine or rebuild the chronology, and guidelines for obtaining the most useful dates are discussed. Dates recently obtained from the site of Chamical in the southern highlands of Ecuador are evaluated according to those guidelines, and they suggest Inca expansion to the north began 1 to 2 decades earlier than allowed in the traditional chronology. The chronology of Inca expansion presented in the Spanish chronicles is called into question by these and other dates, and by a reconsideration of the nature of sources of Inca history utilized by Spanish writers. Evidence suggests a primary Inca form of recording provincial conquests resulted in lists that were ordered geographically. However, those records were interpreted by colonial writers as being chronologically ordered, which led to written histories of Inca expansion that are not consistent with the actual historical sequence of events. As a result, the preferred approach to building a chronology of Inca expansion should be based on 14C dates, with historical sources used to supplement rather than structure the timeline.

One of the largest sources of uncertainty in radiocarbon dating stems from the sample pretreatment procedures used to minimize contamination. A major source of carbon contamination in charcoal from archaeological sites is humic substances carried by groundwater. Here we present a method, independent of 14C dating itself, to evaluate the effectiveness of the cleaning procedure of charcoal. Raman spectra of mixtures of humic substances (HS) and laboratory prepared charcoal indicate that Raman spectroscopy can be used as a semi-quantitative measure of the amount of humic substances associated with archaeological charcoal. Raman spectral analysis of archaeological charcoal samples subjected to different cleaning regimes supports this contention. Such measurements can provide quality control for charcoal preparation procedures and may assist in the interpretation of carbon-dating results.

We constructed a semi-automated system to transform carbonate samples to CO2, as a means to increase sample-processing capacity. The physico-chemical process includes hydrolysis of carbonate, quantification of the mass of carbon and CO2 collection in a glass ampoule. The system is computer-controlled and monitored, and all the data are stored. A single run of five consecutive samples requires about 3.5 hours. Measurements of 14C concentrations were made on samples of IAEA C-1 Carrara marble to test the reliability of this semi-automated system. These measurements have allowed the determination of the total system background and the memory effect of our system.

Radiocarbon accelerator mass spectrometry (AMS) techniques were used to date total organic carbon and plant seeds in the lFs core sequence (36°48′N, 100°08′E) from Qinghai Lake, China. This core was drilled ∼18 m into Qinghai Lake sediments as part of an international cooperative research project, “Scientific Drilling at Qinghai Lake in the Northeastern Tibetan Plateau: High-Resolution Paleoenvironmental Records of Eastern Asia Linked to Global Change,” which began in 2004. Based on the differences in lithology and total organic content (TOC) in core lFs, the core was divided into 3 sections for age-modeling purposes: the upper ∼499 cm lacustrine silty clay to clay; the middle unit of silty clay with silt layers from 499–901 cm; and the lower 901–1861 cm silty clay, loess-like silt, and fine sand layers. Three different approaches are applied to the reservoir age problem. First, a simple linear regression gives an offset of 1342 yr. If the core is divided into three sections, linear regressions can be applied separately for the three segments, which results in an age estimate for the average hardwater effect of ∼135 yr BP for the surface section up to 499 cm. If extrapolated for deeper sections, these results imply a higher reservoir offset for those two sections, which may be as much as 1143 and 2523 yr, but this assumes that there are no discontinuities in the core. A third approach using a wiggle-matching approach gave an offset of 196 yr. This study concludes that the reservoir age of Qinghai Lake is complex, but these new data add to our understanding of the 14C chronology of Qinghai Lake for the last 32 ka.

W F Libby's new dating method from the 1940s, based on experience in physics and chemistry, opened possibilities to check and revise chronologies built on other principles than radioactive decay. Libby's method initially implied collaboration with archaeologists to demonstrate that it worked but also with physicists to improve the technique to measure low β– activities. Chemists, geophysicists, botanists, physiologists, statisticians, and other researchers have contributed to a prosperous interdisciplinary development. Some pitfalls were not recognized from the beginning, although issues such as contamination problems were foreseen by Libby. Pretreatment of samples was discussed very early by de Vries and collaborators, among others. This subject has not yet been abandoned. Closely related to pretreatment is the choice of fraction to be dated and chemicals to be used, especially for accelerator mass spectrometry (AMS) measurements. Calibration against tree rings and comparison with dates obtained using other methods as well as intercomparison projects are partly history but still very actual. The impact by man and climate is also studied since the early days of the method. Also, the carbon cycle has been of great interest. The tools for measurements and statistical analysis have been improved during these first 3 or 4 decades, allowing interpretations not possible earlier. δ13C determinations are mostly very important and useful, but sometimes they have been misleading in discussions of the origin of carbon, especially for human tissues—the metabolism was not yet fully understood. The history and development of the method can only be illustrated by selected examples in a survey like this.

Many lacustrine chronology records suffer from radiocarbon reservoir effects. A continuous, accurate varve chronology, in conjunction with accelerator mass spectrometry (AMS) 14C dating, was used to determine the age of lacustrine sediment and to quantify the past 14C reservoir effect in Sugan Lake (China). Reservoir age varied from 4340 to 2590 yr due to 14C-depleted water in the late Holocene. However, during the Little Ice Age (LIA), 14C reservoir age was relatively stable. According to this study, 14C reservoir age in the late Holocene may be driven by hydrological and climatic changes of this period. Therefore, special caution should be paid to the correction of the 14C reservoir effect by a unique 14C reservoir age in paleoclimatic and paleolimnological study of northwest China.

14C measurements were made on present-day plant material with short integration times (tree leaves and sprouts) in the Eifel area, western Germany, where ancient volcanism produces gaseous emanations of considerable yield. Plants growing near sources emanating 14C-free CO2 show a significant depletion in the period of their growth. The same effect is found in the 14C content of recent samples from the Thera (Santorini) Archipelago/Greece. This mixing of “dead” CO2 may lead to pseudo ages in archaeologic or geologic samples of up to 1600 years in samples from the vicinity of CO2 emanating sources.

To obtain a precise radiocarbon Holocene chronology in coastal areas, it is necessary to estimate the modern 14C reservoir age R(t) and its possible variations with time in relation to paleoenvironmental changes. The modern reservoir 14C age was estimated by comparing AMS 14C ages of 2 recent mollusk shells found in sediment cores sampled in the Palavasian lagoonal system (south of France) with ages derived from 210Pb and 137Cs data and historical accounts of identifiable storm events. The calculated modern R(t) value of 943 ± 25 14C yr is about 600 yr higher than the global mean sea surface reservoir age. This high value, probably due to the relative isolation of the lagoon from marine inputs, is in good agreement with other R(t) estimates in Mediterranean lagoonal systems (Zoppi et al. 2001; Sabatier et al. 2008). 14C ages were also obtained on a series of Holocene mollusk shells sampled at different depths of the ∼8-m-long core PB06. Careful examination of the 14C ages versus depth relationships suggests that R(t) in the past was lower and similar to the value presently measured in the Gulf of Lion (618 ± 30 14C yr, Siani et al. 2000). The change in R(t) from 618 to 943 yr is thought to result from final closure of the coastal lagoon by the sandy barrier, due to the along-shore sediment transfer.

High precision for radiocarbon cannot be reached without profound insight into the various sources of uncertainty which only can be obtained from systematic investigations. In this paper, we present a whole series of investigations where in some cases 16O:17O:18O served as a substitute for 12C:13C:14C. This circumvents the disadvantages of event counting, providing more precise results in a much shorter time. As expected, not a single effect but a combination of many effects of similar importance were found to be limiting the precision.

We will discuss the influence of machine tuning and stability, isotope fractionation, beam current, space charge effects, sputter target geometry, and cratering. Refined measurement and data evaluation procedures allow one to overcome several of these limitations. Systematic measurements on FIRI-D wood show that a measurement precision of ±20 14C yr (1 σ) can be achieved for single-sputter targets.

A multicounter radiocarbon dating system was developed applying the experiences of the previous one-channel low-level counting facility. The counter system consists of nine electrolytic copper proportional counters of identical diameters with sensitive volumes of 0.35–0.7dm3 and filled with either methane at high pressure (6 bar) or CO2 at 1 bar. The inner counters are surrounded by an anticoincidence shield consisting of five multiwire proportional flat counters filled with propane. The pulses of the detectors are handled by integrated amplifiers, discriminators and anticoincidence units interfaced to a microprocessor-controlled data evaluation unit. Software is written in BASIC using ASSEMBLER sub-routines. The overall precision of the system for modern carbon samples using high-pressure methane-filled counters (B ≍ 0.7 cpm, S ≍ 14 cpm) is better than 4 after a counting period of seven days.

This list contains dates related to the chronology ofthe last glaciation in Europe. Since several of theolder results which already have appeared in printneed correction or re-interpretation it wasconsidered necessary to incorporate as many of themas possible into this list. Notably the datespublished by de Vries (1958) are included here andreconsidered in the light of our presentunderstanding of the climatic succession. It isnoteworthy that, although the interpretation mayhave changed slightly, most of those measurementsare still as valid today as they were eight yearsago.

The Keck Carbon Cycle accelerator mass spectrometry facility at the University of California, Irvine, operates a National Electronics Corporation 40-sample MC-SNICS ion source. We describe modifications that have increased beam current output, improved reliability, and made the source easier to service.

The different categories of samples and their treatments at the radiocarbon (14C) laboratory in Jena, Germany, are described. The Jena 14C laboratory is dedicated to studying the global carbon cycle through the analysis of soil, plant, gas, charcoal, and wood samples. The respective preparation procedures for different samples types are presented, including wet-chemistry pretreatments for soil decalcification, charcoal purification using an acid–base–oxidation procedure (ABOx), and α-cellulose extraction from wood and leaves. In particular, investigations of the background corrections for each sample type are emphasized. Furthermore, an investigation of the contamination resulting from the storage of graphite is presented. Four storage conditions are investigated for storage times up to 30 months.

A method has been developed at the Arizona AMS facility for production of graphite directly from CO2 by catalytic reduction of CO/H2 mixtures. The method is a modification of procedures discussed by Vogel et al (1984). Currents of 12C− from these targets vary considerably, but have a median value which is 70% of that achieved from spectroscopic graphite. Precisions of ±60 to 100 yr are routinely achieved for 14C ages of 5000-yr-old samples containing one milligram of carbon. The yield of 14C from “blank” targets is 0.6 ± 0.1% of that from modern material.

In 1969, at the Nobel Symposium on “Radiocarbon Variations and Absolute Chronology” in Uppsala, a curve was presented that illustrated the functional dependence of measured conventional radiocarbon dates on true historical ages of wood samples (Suess, 1971). The curve was derived from the results of La Jolla measurements of radiocarbon in bristlecone pine wood dendrochronologically dated by and obtained from Professor C W Ferguson of the University of Arizona (Ferguson, 1968). The curve was intended to be adequate for deriving calibrated radiocarbon dates and also for allowing fairly reliable estimates of the accuracy of the absolute dates obtained in this manner. The basis for the validity of this calibration is the well known fact that, for all practical purposes, wood samples that had grown at the same time show the same radiocarbon content. However, the reverse is not always true: Wood samples showing the same radiocarbon content do not necessarily have the same age because of the windings and steps of the curve (Stuiver and Suess, 1966).

Charcoal is the result of natural and anthropogenic burning events, when biomass is exposed to elevated temperatures under conditions of restricted oxygen. This process produces a range of materials, collectively known as pyrogenic carbon, the most inert fraction of which is known as black carbon (BC). BC degrades extremely slowly and is resistant to diagenetic alteration involving the addition of exogenous carbon, making it a useful target substance for radiocarbon dating particularly of more ancient samples, where contamination issues are critical. We present results of tests using a new method for the quantification and isolation of BC, known as hydropyrolysis (hypy). Results show controlled reductive removal of non-BC organic components in charcoal samples, including lignocellulosic and humic material. The process is reproducible and rapid, making hypy a promising new approach not only for isolation of purified BC for 14C measurement but also in quantification of different labile and resistant sample C fractions.

We describe the operation of a commercial system as modified for preparation of CO2 for the CO2 source. AMS samples are automatically combusted in a CHN analyzer, and stable isotope measurements are made on line. We describe the performance of this equipment, with reference to yield, sample contamination, memory effect, accuracy of isotope measurement, convenience and cost. We discuss the current status of dating using the CO2 source. This is the only source in operation at Oxford, and has been in routine dating since September 1989. We assess the practicalities of operation, including the latest measurements on background, memory, sample-size requirements and operating schedules. We also describe modifications to the sputter beam optics and to the gas handling systems.

We show that high-precision radiocarbon (Δ14C) measurements from annual bands of a Hawaiian surface coral decreased by 7‰ from AD 1893 to 1952. This decrease is coincident with the Suess Effect, which is mostly due to the dilution of natural levels of 14C by 14C-free fossil fuel CO2. This decrease is equal to that expected in surface waters of the subtropical gyres, and indicates that the surface waters of the North Pacific were in steady state with respect to long term mixing of CO2 during the past century. Correlation between Δ14C and North Pacific gyre sea surface temperatures indicates that vertical mixing local to Hawaii and the North Pacific gyre as a whole is the likely physical mechanism to result in variable Δ14C. Prior to 1920, this correlation starts to break down; this may be related to the non-correlation between biennial Δ14C values in corals from the southwest Pacific and El Niño events observed during this period as well.

Over the last decade, archaeologists have turned to large radiocarbon (14C) data sets to infer prehistoric population size and change. An outstanding question concerns just how direct of an estimate 14C dates are for human populations. In this paper we propose that 14C dates are a better estimate of energy consumption, rather than an unmediated, proportional estimate of population size. We use a parametric model to describe the relationship between population size, economic complexity and energy consumption in human societies, and then parametrize the model using data from modern contexts. Our results suggest that energy consumption scales sub-linearly with population size, which means that the analysis of a large 14C time-series has the potential to misestimate rates of population change and absolute population size. Energy consumption is also an exponential function of economic complexity. Thus, the 14C record could change semi-independent of population as complexity grows or declines. Scaling models are an important tool for stimulating future research to tease apart the different effects of population and social complexity on energy consumption, and explain variation in the forms of 14C date time-series in different regions.

This list includes age measurements carried out from November 1969 to December 1970. All archaeologic and geologic samples come from Italian territory. Laboratory equipment, largely unchanged, has been described (Alessio et al., 1970).