This work focuses on building a high-resolution age-depth model for quantitative palaeoclimate study from the Mohos peat bog, East Carpathian mountains. The investigated core presents a continuous peat profile for the last 12 kyr. The chronology was based on 36 accelerator mass spectrometry radiocarbon (AMS 14C) analyses of the separated Sphagnum samples from different depths of the profile. Dry Sphagnum samples for AMS dating were prepared using the classic acid-base-acid (ABA) method followed with an oxidative bleaching step to get clean cellulose. Sphagnum cellulose samples were measured by AMS using the EnvironMICADAS at the ICER (Debrecen, Hungary). A high-resolution chronology was obtained with the use of Bayesian age-depth modeling. Peat accumulation rate has been calculated and the sections with variable accumulation rate values were observed along the profile.

We studied a suitable procedure for preparing of water samples used in radiocarbon intercomparisons involving dissolved inorganic carbon (DIC). The water samples must have inter-batch consistency and stable 14C concentrations and no sterilizing agent (e.g., HgCl2) should be added, in order to avoid the production of hazardous material. Six water samples, containing widely different amounts and types of salts, DIC, and 14C concentrations (1–100 pMC), were prepared in order to assess the procedure. Sample consistency was investigated through δ13C and chemical compositions; their low variabilities indicate that our procedure can be applied to radiocarbon intercomparison. A specific sample preparation protocol was developed for this kind of applications.

During the last 60 years, the thickness of the Grel peatland deposits (Polish Inner Carpathians), was decreased twice: from about 7.4 m in 1962, to 3.9 m in 2019. Pollen analyses of peat deposits performed in 1962 (Koperowa 1962) and 2019 (this study) showed that the peatland deposits have accumulated since the Oldest Dryas Stadial up to the present day. Comparative analysis of both palynological profiles was carried out, which exhibits a high consistency of the percentage of pollen of several taxa for the 10 horizons occurring in both profiles. Based on the age–depth curve made for the new profile, the modeled age for the above-mentioned compliance levels was obtained and based on this age, a “retrospective” age–depth model was elaborated for the Koperowa’s profile. The analysis of both profiles showed that the compaction of sediments did not occur proportionally in the entire sequence. The conducted research indicates that contemporary human activity may significantly affect the whole length of peatland profiles, not only their upper parts, as previously was considered. The reconstruction of the palaeoenvironment (palaeoclimate) based on multiproxy analysis of the peatland deposits is capable to precisely document this phenomenon.

The following dates are samples measured since publication of Kiel III (Radiocarbon, v. 10, p. 328–332). Age calculations are based on 95% of the activity of NBS oxalic-acid standard as modern value of A.D. 1950. Results are calculated with Libby half-life and reported in yr before 1950. Error corresponds to 1σ variation of sample net counting rate as well as modern standard and background, but does not include the uncertainty in C14 half-life and in secular C14 variations. Dates are not corrected for isotopic fractionation.

Scintillation counting vials used for counting synthesized benzene accumulate an inside coating which is insoluble in benzene. This coating reduces the photon transfer from the vial and lowers its observed background. Age calculations that include calibration data collected with other vials may be inaccurate if this effect is not considered. Frequent cleaning of the counting vials with strong acid solutions keeps the coating from accumulating.

A sample counting vial cleaned only with photospectrometric grade benzene between 67 different sample benzene fillings made in a 20-month period showed, during counting, an efficiency lowered by 2.8% and a background lowered by 8.7%. Age calculations for a 10 ka old sample made with calibration data from “matched” vials would yield a result too old by 515 yr.

Observation of the ion source generated background has been an area of focus during our routine analytical work. It is noted that the results of very-low-ratio samples are dependent upon the particular procedures for measurement using the present-day Cs+ sputter ion sources. When measured without excessive Cs+ fluxes and without interleafing with other higher-ratio samples and references, the accelerator mass spectrometry (AMS) sensitivity can be somewhat improved. In some cases, it appears possible to assess old radiocarbon (14C) samples to beyond the long-standing 60 kyr limit. A number of observational studies are made for the sole purpose of minimizing the final contamination to the rare isotopes that is generated within the ion source.

The “shielding” efficiency of the guard counters has been a main scope of the present investigation. Our special guard counters consist of closed shells (ca 3cm thick) filled with propane at 1.2 atmospheres pressure. These guard counters are nearly 100 percent efficient against charged particles, and 1 to 2 percent against gamma and neutrons. The efficiency has now been studied more in detail in an arrangement with four guard shells around a 14C counter. For each extra guard shell, the cosmic fraction of the counter background was reduced by ca 13 percent. The reduction does not involve penetrating high energy charged particles, but is related to γ ray showers penetrating the guards. A thicker old lead shield between 14C counter and the guard counters also reduces the background and serves the same purpose. In order to approach underground conditions for the 1.5 liter counter background (0.32 ± 0.01 c/min), most of the shielding material has to be put inside guard shells. An ordinary guard counter combined with an extra guard on top of the iron shield is very efficient. A background of 0.48 ± 0.01 c/min has already been obtained.

Carmi (2002) is a response to our study published in Radiocarbon 43(1) by Rasmussen et al. (2001). We noted widespread possible exposure to castor oil of the Dead Sea Scrolls (DSS) in the Rockefeller Museum in the 1950s and reported experiments showing that the AAA pretreatment used in the first 2 series of radiocarbon datings of the DSS (Bonani et al. [1992] and Jull et al. [1995]), “cannot be guaranteed to have removed all of the modern carbon in any samples if they had been contaminated with castor oil and hence could have produced some 14C dates that were younger than the texts' true ages.” Carmi, a coauthor of the Bonani et al. (1992) study, criticizes our analysis on 4 grounds:

This list includes the results of datings made during 1970–71. The methods of measurements are the same as described in R., 1971, v. 13, p. 29–31.

A signal of rapid changes in 14C production is logged in annual series of 14C derived from tree rings, which can be associated with diverse effects of cosmic-ray fluxes, including solar burst and supernova events. These 14C signatures may vary in time and space. The intensity and structure of the 14C signal is multifaced, which complicates understanding of the forcing and attribution of the underlying astrophysical events. It was suggested that Δ14C in 1052/53 CE and 1054/55 CE signatures at a 4‰–6‰ range over two years could be caused by the Crab Nebula supernova (SN1054) or/and solar perturbation. The temporal incoherence of the signals in published 14C series is investigated with dynamic time warping (DTW), novel approach for matching time-behavioral patterns in multiple 14C datasets. DTW analysis of four 14C signatures from tree rings of California, Finland and England suggests that 14C spikes between 1052 CE and 1055 CE can be caused by a single event. The flickering fingerprint may result from cross-dating inconformity. Cross-checking of tree-ring records from distant locations is impossible sometimes due to large difference in environmental conditions limiting tree growth. The methodology helps to align the signals and can be applied to other 14C datasets.

Sequential thermal analysis allows for deconvoluting the refractory nature and complexity of carbon mixtures embedded in mineral matrices for subsequent offline stable carbon and radiocarbon (14C) isotope analyses. Originally developed to separate Holocene from more ancient sedimentary organic matter to improve dating of marine sediments, the Ramped Pyrolysis and Oxidation (RPO) apparatus, or informally, the “dirt burner” is now used to address pressing questions in the broad field of biogeochemistry. The growing interest in the community now necessitates improved handling and procedures for routine analyses of difficult sample types. Here we report on advances in CO2 purification during sample processing, modifications to the instrumentation at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility, and introduce sodium bicarbonate procedural standards with differing natural abundance 14C signatures for blank assessment. Measurements from different environmental samples are used to compare the procedure to the different generations of sequential thermal analyses. With this study, we aim to improve the standardization of the procedures and prepare this instrumentation for innovations in online stable carbon isotopes and direct AMS-interface measurements in the future.

It is important to know how much of the increased atmospheric CO2 is derived from fossil fuel emissions. Here, we review the progress in atmospheric fossil fuel CO2 (CO2ff) tracing over recent years by measurement of Δ14C in Chinese cities. In this paper we make progress by expanding the analysis from some locations to more regional views, by combining observations with modeling, and by making a preliminary comparison of observation-derived CO2ff with inventory-derived CO2ff. We have obtained a general picture of Chinese urban CO2ff and characteristics of its spatio-temporal variations at different scale, and identified the corresponding influencing factors. Interestingly, we found that the weekend effect of CO2ff was less evident in Chinese cities. In addition, we observed simultaneous variations in CO2ff and PM2.5 in a winter haze event in Beijing and a simultaneous decrease in annual averages of CO2ff and PM2.5 in Xi’an based on multi-year (2011–2016) Δ14CO2 monitoring. We found that local coal combustion was the main source of CO2ff in Xi’an, which is located in the Guanzhong basin, by applying a WRF-Chem model and looking at δ13C signatures. Thus, reduction of coal consumption is a crucial target for carbon emissions reduction in China.

Paleokarst forms in raised beach deposits of Southwest England and South Wales and generally known as “pipes” were dated by 14C and thermoluminescence (TL) methods. Current geological opinion is that these pipes are features that developed under the cover of periglacial-solifluctional deposits due to periglacial conditions prevalent in the Late Devensian. In the present study, TL was used to determine the age of quartz grains forming the raised beaches. 14C ages were obtained from carbonate cements within sandrock and on the pipe walls. TL ages measured for quartz grains separated from sandrock samples are older than 80 ka bp, whereas the corresponding TL dates obtained from the sandy material of pipe infills center around 40 ka bp. All carbonates yielded finite apparent 14C dates that range from ca. 45 ka bp to 27 ka bp for sandrock. The apparent 14C dates obtained on carbonate cements from the pipe walls fall into two groups, one ranging from 30 ka bp to 22 ka bp and the other from 15 ka bp to 7 ka bp. On the basis of geochemical considerations, we conclude that the sandrock cements formed between 35 and 25 ka bp and pipe walls cemented between 30 and 2 ka bp with a break during the climate deterioration caused by last ice sheet advance.

A small 200ml capacity CO2 proportional counting system has been developed which uses only 100mg of carbon for complete filling. Thus, with respect to the small quantities needed, it compares favorably to dedicated accelerators at significantly lower cost. The performance of this equipment is demonstrated using a variety of samples including some human bone fragments from La Jolla which had been estimated to be 28,000 years old by aspartic acid racemization analysis.

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.

An informal collaborative group of radiocarbon dating laboratories, the Low-Level Club, has been established to measure the gamma radiation flux and to test the efficiency of the anticoincidence counting system in laboratories with a NaI detector unit. The detector will record gamma radiation from cosmogenic nuclides, muons and secondary γ radiation formed in the passive shield by charged cosmic-ray particles. We present here the first phase of this work.

Least-squares fitted smooth curves to radiocarbon versus tree-ring calibration data for the period AD 1140 to 1950 are compared with climatic warming and cooling of the North Atlantic (Little Ice Age), and with recorded sunspot numbers over the period AD 1670 to 1950.

Calibration curves from different parts of the globe are not identical, and appear to be determined by a combination of variable solar activity and variable oceanic upwelling of 14C-depleted water, with the variable upwelling itself partly determined by solar activity.

The use of radiocarbon dating in geocryological investigations makes it possible to establish a chronology for permafrost-geological development during the Late Pleistocene. Both global and regional time scales for the formation of Late Pleistocene permafrost have been worked out over the past 15–20 years at the Permafrost Institute of the Siberian Branch of the Russian Academy of Sciences. I present here results from study areas of northwestern Siberia and of North, Central and West Yakutia.

The following list sums up the results of radiocarbon age determinations obtained at the Laboratory in 1974-1975. The list is prefaced with a brief description of the measurement procedure and discussion of some methodological aspects of the investigation that result in a higher accuracy of dating.