For radiocarbon calibration, the arrow of time is pointing backwards but the entropy does not necessarily decrease in this direction…

Bayesian mathematics provides a tool for combining radiocarbon dating results on findings from an archaeological context with independent archaeological information such as the chronological order, which may be inferred from stratigraphy. The goal is to arrive at both a more precise and a more accurate date. However, by means of simulated measurements we will show that specific assumptions about prior probabilities—implemented in calibration programs and not evident to the user—may create artifacts. This may result in dates with higher precision but lower accuracy, and which are no longer in agreement with the true ages of the findings.

When introduced almost five decades ago, radiocarbon (14C) dating provided New World archaeologists with a common chronometric scale that transcended the countless site-specific and regional schemes that had been developed by four generations of field researchers employing a wide array of criteria for distinguishing relative chronological phases. A topic of long standing interest in New World studies where 14C values have played an especially critical role is the temporal framework for the initial peopling of the New World. Other important issues where 14C results have been of particular importance include the origins and development of New World agriculture and the determination of the relationship between the western and Mayan calendars. It has been suggested that the great success of 14C was an important factor in redirecting the focus of American archaeological scholarship in the 1960s from chronology building to theory building, led to a noticeable improvement in US archaeological field methods, and provided a major catalyst that moved American archaeologists increasingly to direct attention to analytical and statistical approaches in the manipulation and evaluation of archaeological data.

The Swedish varve chronology, or Swedish Time Scale, is an annual chronology based upon the successive correlation of more than 1000 varve-thickness diagrams. The Late Glacial-Early Holocene varved clays were deposited as glaciolacustrine sediments in the Baltic Sea during the recession of the Scandinavian ice sheet. Formation of varved clays continued throughout the Holocene and is still going on in the estuary of River ångermanälven in northern Sweden. Accelerator mass spectrometry (AMS) radiocarbon measurements, which have been performed on terrestrial plant macrofossils extracted from the varved clays, show—in comparison with other annual chronologies—that several hundreds of varve years are missing in the varve chronology. These findings are supported by, among others, pollen stratigraphic investigations on time-equivalent varve year intervals. If an effort were undertaken to evaluate the erroneous parts, the Swedish Time Scale would have the potential of becoming a continuous annual chronology.

This paper presents radiocarbon dates of terrestrial macrofossils from Lakes Gościąż and Perespilno, Poland. These data agree very well with most of the German pine calibration curve. In the Late Glacial, they generally agree with the data from Lake Suigetsu, Japan, and indicate constant or even increasing 14C age between 12.9 and 12.7 ka BP, rapid decline of 14C age around 12.6 ka BP, and a long plateau 10,400 14C BP around 12 ka BP. Correlation with corals and data from the Cariaco basin seems to support the concept of site-speficic, constant values of reservoir correction, in contradiction to those introduced in the INTCAL98 calibration. Around the Allerød/Younger Dryas boundary our data strongly disagree with those from the Cariaco basin, which reflects large discrepancy between calendar chronologies at that period. The older sequence from Lake Perespilno indicates two periods of rapid decline in 14C age, around 14.2 and 13.9 ka BP.

Half a century since radiocarbon was first used in the archaeology of the Old World, it seems that the expectations of W F Libby may be becoming a reality. In 1952 (Libby 1952:97), he wrote:

Archaeologists, geologists and palynologists are continually searching for the means to improve methods of counting time. The … relative chronologies lack precision and direct correlation with the calendar, except when they may be checked with, … for example, the calendar based on tree-ring counts.

During the last decade, several radiocarbon-dated varve chronologies have been produced. The main goal at first was the extension of the 14C calibration curve beyond 10,000 BP. This paper aims to discuss varve chronologies of Soppensee and Holzmaar Lakes. Although both chronologies encountered problems, high-resolution 14C dating and relative varve time have been obtained for events during the Late Glacial.

For the majority of dating laboratories and their respective user communities, the journal Radiocarbon is no longer regarded as the medium for primary publication of radiocarbon measurements. In compliance with editorial policy, the emphasis has long since moved towards the publication of research papers on technological enhancements and applications of 14C as well as other cosmogenic isotopes and this has left a requirement for an alternative medium for the publication of date lists per se. In the late 1980s, an International Radiocarbon Data Base was proposed by Renee Kra (then the managing editor) but limitations in computer and communications technologies together with the inevitable financial implications meant that this timely concept could not be taken to completion. In the last year, we have taken advantage of the development of the worldwide web to compile a database of 14C age measurements of a Scottish archaeological nature which can be found at the web address http://www.historic-scotland.gov.uk/.

A comparison of radiocarbon histograms of samples controlled and uncontrolled for sample provenance and composition factors indicates that differences are sufficiently large to influence the discrimination of alternative hypotheses on the age of the important, early Bellows Dune site in Hawai'i.

A new suite of five dates on a whale rib from Varangerfjord was completed on different fractions obtained by EDTA treatment. The intention was to test the possible influence of contaminants, the criteria for complete reactions, and the reliability of the treatment in light of scattered values obtained earlier on samples from Varangerfjord. The yield on the treatment of the selected bone did, however, not allow any general conclusions regarding the influence of contaminants in nature. The results are interesting from an inter-sample comparison point of view. Included are observations, made during treatment, of pH and color changes as well as the appearance of the samples. These observations are provided as a reference for deciding when the treatment is complete.

The Holocene varve chronology of annually laminated sediment sequences from Lake Meerfelder Maar agree for most of the record with dendro-calibrated accelerator mass spectronomy radiocarbon dates from the same site. Only between 9710 and 9950 cal BP does an offset of 240 yr appear between both data sets. At this position, a micro-disturbance in the varve succession has been detected by thin section analyses and was quantified in terms of missing varves. A comparison with the nearby record from Lake Holzmaar, as well providing high resolution AMS 14C and varve chronologies, revealed that such gaps (ca. 2% in time for the entire Holocene) are exceptional for these long-varved maar lake records. Moreover, since sections of missing years appear for both profiles at different stratigraphic positions, a combination of both the Meerfelder Maar and Holzmaar records enables us to bridge erroneous zones in varve chronologies. This confirms the high potential of two long-varved records in close vicinity to each other for the elimination of dating errors and for increasing chronological precision at a time resolution that is normally regarded as within the counting errors. Late Glacial varve and 14C data beyond the dendro-calibration from Meerfelder Maar and their tentative tele-connections to other high resolution data sets reveal unexplained age discrepancies in the calendar year time scale of about 200 years.

We present a method for the isolation of phenolic compounds derived from lignin for radiocarbon analysis. These phenols are generated by chemical oxidation of polymeric materials and derivatized for separation and recovery by preparative capillary gas chromatography (PCGC). This technique yields tens of micrograms of pure, stable compounds that can be converted to graphite and analyzed by accelerator mass spectrometry (AMS). Analysis of model flavor compounds and dated woods indicates that, in most cases, the radiocarbon (14C) contents of the individual compounds, corrected for the contribution of the derivative, agree with that of the bulk material to within 20%.

This paper presents an updated atmospheric radiocarbon calibration from annually laminated (varved) sediments from Lake Suigetsu (LS), central Japan. As presented earlier, the LS varved sediments can be used to extend the radiocarbon time scale beyond the tree ring calibration range that reaches 11,900 cal BP. We have increased the density of 14C measurements for terrestrial macrofossils from the same core analyzed previously. The combined data set now consists of 333 measurements, and is compared with other calibration data.

The publication during the 1990s of Greenland ice-core records spanning the transition from the Last Cold Stage to the present interglacial (ca. 14–9 14C ka BP) presented new challenges to scientists working on marine and terrestrial sequences from this important time interval. In particular, there is now an overriding imperative to increase the levels of precision by which events during this period can be dated and correlated. We review some of the problems commonly encountered when using radiocarbon dating for these purposes, and consider some of the new approaches that will be required if this dating method is to provide a basis for a high precision chronology for the last glacial-interglacial transition.

A radiocarbon chronology has been developed using shell, bulk peat, and paired charcoal and pollen preparations from a peat and clay sequence in southwestern Australia. The results indicate the sequence is of Holocene age, and the mid-Holocene was a period of rapid sediment deposition. The earliest record is based on Bothriembyron sp. snail shell and there is a strong indication that the deposit had a stratigraphic hiatus between 9600 and 4700 BP. Modern shell of the snail has no ancient reservoir effect. The bulk peat ages were a little younger than associated AMS determinations on hand-picked charcoal and residues from pollen preparations. As a group, paired charcoal and pollen based dates were indistinguishable in age. This implies that the sedimentary charcoal shows no significant storage and transport time in the catchment before deposition. This is important when interpreting pollen records and sedimentary charcoal to reconstruct fire and vegetation dynamics and inter-relationships.

Uranium series and radiocarbon ages were measured in corals from the uplifted coral terraces of Huon Peninsula (HP), Papua New Guinea, to provide a calibration for the 14C time scale beyond 30 ka (kilo annum). Improved analytical procedures, and quantitative criteria for sample selection, helped discriminate diagenetically altered samples. The base-line of the calibration curve follows the trend of increasing divergence from calendar ages, as established by previous studies. Superimposed on this trend, four well-defined peaks of excess atmospheric radiocarbon were found ranging in magnitude from 100% to 700%, relative to current levels. They are related to episodes of sea-level rise and reef growth at HP. These peaks appear to be synchronous with Heinrich Events and concentrations of ice-rafted debris found in North Atlantic deep-sea cores. Relative timing of sea-level rise and atmospheric 14C excess imply the following sequence of events: An initial sea-level high is followed by a large increase in atmospheric 14C as the sea-level subsides. Over about 1800 years, the atmospheric radiocarbon drops to below present ambient levels. This cycle bears a close resemblance to ice-calving episodes of Dansgaard-Oeschger and Bond cycles and the slow-down or complete interruption of the North Atlantic thermohaline circulation. The increases in the atmospheric 14C levels are attributed to the cessation of the North Atlantic circulation.

Appropriate management strategies are essential for the protection and maintenance of groundwater resources. It is therefore important that aquifers are understood in terms of hydraulics, recharge, and yield potential, and that the vulnerability of aquifers to surface pollution is evaluated. A range of aquifer types were examined in this study, and water samples were analyzed for the radiocarbon content of the total dissolved inorganic carbon (TDIC), stable isotopes, and a suite of chemical and physical parameters. The data were input to a selection of models for the estimation of the initial activity of the TDIC, and groundwater ages were calculated. Eight commonly used models were comparatively assessed in the study. The Tamers, Mook, and IAEA models gave anomalous ages, probably because of their inability to correct for solid phase isotopic exchange in aquifers. The Pearson, F&G, Evans, Eichinger, and Mass Balance models produced results in broad agreement.

The study shows that contrary to popular belief, there are sources of ancient groundwater in Ireland. Of the 19 sampling stations, two boreholes yielded waters with age estimates of greater than 10,000 BP. Water samples from a further six sites returned ages of between around 800 and 4000 BP. In contrast to borehole samples, spring wells yielded water of consistently young ages, demonstrating rapid recharge and flow mechanisms. Samples from several spring wells produced negative ages, indicating the presence of anthropogenic 14C. The findings demonstrate the potential for contamination of springs by surface runoff, while sources of greater age generally offer a greater degree of protection from surface pollution.