We are observing a dramatic increase of CO2 in the atmosphere, unprecedented in the last several million years. Carbon isotopic ratios have been very useful in helping to untangle the respective roles of anthropogenic emissions and sources/sinks of CO2 in the oceans or terrestrial biosphere. However, this untangling has not been as simple as was often hoped. The isotope ratio signatures produced by emissions and removals that are present in atmospheric CO2 are always vigorously being erased by isotopic exchange with the oceans and terrestrial ecosystems, without there necessarily being any effect on total CO2. Especially in the last decades this pure isotopic exchange effect has led to gross errors that have clouded the public debate on climate change, obscuring mankind’s role. This paper traces my own struggle with the scientific and public sides of this issue, which I ran into from the start of my career in Groningen and throughout my years at NOAA. It is still relevant today.

We present accelerator mass spectrometry radiocarbon (AMS 14C) dating results of the “Jochi Khan Mausoleum”—the proposed burial place of the oldest son of Gengghis Khan in Ulytau, Kazakhstan. The Ulytau region retains 34 burial complexes of Islamic tradition associated with the Golden Horde history (1221–1438 CE). However, there is no calendar-dated chronology of the medieval mausoleums in this region, which complicates their historical interpretation. Three 14C dates from construction timbers and burial of the Jochi Khan mausoleum are calibrated to 1220–1400 CE interval (95.4% range) with the mid-point at 1245 CE for the coffin, 1330 CE for the entry door, and 1350 CE for a masonry wall. The 14C-calibration suggests that the mausoleum was built about 100 years after the death of Jochi (1225 CE) and renovated at least once in the middle of the 14th century. Apparently, the wood for the coffin was harvested sometime in the interval 1220–1270 CE. The calendar ages of the coffin and the mausoleum are ca. 75 years apart. It is possible that the old coffin was placed into a newly constructed mausoleum. However, there is no historical evidence confirming this important re-burial of Jochi. The dating results challenge the attribution of the mausoleum to Jochi Khan. This study demonstrates that the age of the Islamic mausoleums in Ulytau can be successfully dated with 14C. While requiring further data assembly, this first 14C dataset can form the basis of the calendar chronology of the Golden Horde in Kazakhstan. Historical attribution of the mausoleums must be collaborated with the calendar chronology.

Radiocarbon (14C) dating is often carried out upon multi-specimen samples sourced from bioturbated sediment archives, such as deep-sea sediment. These samples are inherently heterogeneous in age, but existing 14C calibration techniques were originally developed for age homogeneous material, such as archaeological artifacts or individual tree rings. A lack of information about age heterogeneity leads to a systematic underestimation of a sample’s true age range, as well as the possible generation of significant age-depth artifacts during periods of the Earth’s history coinciding with highly dynamic atmospheric Δ14C. Here, a new calibration protocol is described that allows for the application of sedimentological priors describing sediment accumulation rate, bioturbation depth and temporally dynamic species abundance. This Bayesian approach produces a credible calibrated age distribution associated with a particular laboratory 14C determination and its associated sedimentological priors, resulting in an improved calibration, especially in the case of low sediment accumulation rates typical of deep-sea sediment. A time-optimized computer script (biocal) for the new calibration protocol is also presented, thus allowing for rapid and automated application of the new calibration protocol. This new calibration protocol could be applied within existing age-depth modeling software packages to produce more accurate geochronologies for bioturbated sediment archives.

Isotopic analysis of Micropogonias furnieri otoliths were used to get insight into palaeoceanographic conditions in the Guanabara Bay and Saquarema Lagoon, Rio de Janeiro state (RJ), located on the southeastern coast of Brazil, under upwelling influence of the Cabo Frio system. Archaeological otoliths come from two Holocene shellmounds (or sambaquis): Galeão and Beirada. For the first time, radiocarbon analysis using high accuracy techniques were performed at Galeão. Age range was determined to be between 5820 and 4980 cal BP, which extends the chronology of human settlement in the Guanabara Bay. Micro-samples of the otoliths were collected sequentially from the core to the edge, to provide continuous δ18O and δ13C isotopic profiles over the lifetime of the individual fish. Derived-δ18Ooto palaeotemperature estimates vary according to seasonality, resulting in a palaeoceanographic variation between 8 to 31°C for Guanabara Bay and 8 and 28°C for the Saquarema Lagoon. Our data indicate that whitemouth croakers were captured during the Middle Holocene from the Guanabara Bay and Saguarema Lagoon and resided in cooler temperatures compared to temperatures of current conditions.

Terrestrial environments tend to be characterized by an incomplete record of past conditions. For the MIS 3–2 periods, there is only one known site in Poland—Horoszki Duże—in which a probably continuous record of climate change has been preserved. However, this site does not have any high precision multi-proxy analyses. In the absence of continuous high-resolution records, we decided to gather and analyze scattered information. We assembled data originating from various sites in Poland and checked whether the available results of 14C and luminescence dating presented in the form of probability density distributions (PDF) and kernel density estimation (KDE) models would allow their reinterpretation. The data were compared to the Greenland isotope curve to see whether they were consistent with the hypothesis that the number of “warming-cooling” cycles recorded in the examined sediments was of the same order as in those ice-core records. Previously in Poland, usually only two interstadial periods (i.e., Hengelo and Denekamp, 36–38.6 and 28–32 14C kBP, respectively) have been identified in the discussed period. The joint analysis of data from a larger area revealed more warming-cooling events than recorded from individual sites.

An application of radiocarbon (14C) in atmospheric chemistry is reviewed. 14C produced by cosmic neutrons immediately forms 14CO, which reacts with hydroxyl radicals (OH) to 14CO2. By this the distribution and seasonality (the lifetime of 14CO is ∼1 month) of the pivotal atmospheric oxidant OH can be established. 14CO measurement is a complex but unique application which benefitted enormously from the realization of AMS, bearing in mind that 14CO abundance is of the order of merely 10 molecules per cm3 not only provides 14CO an independent measure for the OH based self-cleansing capacity of the troposphere, but also enabled detection of 14C production due to high energy solar protons in 1989. Although its production takes place throughout the atmosphere and does not have the character of a point source, transport processes in the atmosphere affect the distribution of 14CO. Vertical mixing in the troposphere renders gradients in its production rate less critical, but considerable meridional gradients exist. One question has remained open, namely confirmation of calculated 14C production by direct measurement. A new sampling method is proposed. The conclusions are a guide to future work on 14CO in relation to OH and atmospheric transport.

Late Holocene relative sea-level reconstructions are commonly generated using proxies preserved in salt-marsh and mangrove sediment. These depositional environments provide abundant material for radiocarbon dating in the form of identifiable macrofossils (salt marshes) and bulk organic sediment (mangroves). We explore if single-step graphitization of these samples in preparation for radiocarbon dating can increase the number and temporal resolution of relative sea-level reconstructions without a corresponding increase in cost. Dating of salt-marsh macrofossils from the northeastern United States and bulk mangrove sediment from the Federated States of Micronesia indicates that single-step graphitization generates radiocarbon ages that are indistinguishable from replicates prepared using traditional graphitization, but with a modest increase in error (mean/maximum of 6.25/15 additional 14C yr for salt-marsh macrofossils). Low 12C currents measured on bulk mangrove sediment following single-step graphitization likely render them unreliable despite their apparent accuracy. Simulated chronologies for six salt-marsh cores indicate that having twice as many radiocarbon dates (since single-step graphitization costs ∼50% of traditional graphitization) results in narrower confidence intervals for sample age estimated by age-depth models when the additional error from the single-step method is less than ∼50 14C yr (∼30 14C yr if the chronology also utilizes historical age markers). Since these thresholds are greater than our empirical estimates of the additional error, we conclude that adopting single-step graphitization for radiocarbon measurements on plant macrofossils is likely to increase precision of age-depth models by more than 20/10% (without/with historical age markers). This improvement can be implemented without additional cost.

Wally Broecker’s puzzles required radiocarbon dating in order to solve them.

Caves containing perennial ice deposits make up a little-known, but emerging part of the cryosphere under increasing scrutiny from the scientific community. M-17, a sag-type ice cave opening at 1879 m asl in the Tolminski Migovec massif of the Julian Alps (NW Slovenia) contains a perennial underground ice deposit whose paleoclimate sensitivity is poorly understood and whose longevity under current climate change is at risk. The past mass balance of this cave is constrained using wood macro-remains embedded in ice. Accelerator mass spectrometry radiocarbon dating of 18 wood samples embedded in ice provides the largest currently available dataset for a subterranean ice deposit in the southern European Alps. The reconstructed chronostratigraphy reveals three main phases of likely positive ice balance around 900–1100 AD, 1200–1300 AD, and 1700–1800 AD, as well as a period of negative mass balance around 1300–1400 AD. The onset of cave glaciation is deemed to have occurred no later than about 900 AD, with evidence of overall positive ice mass balance during multi-decadal periods characterized by cooler-than-average summers and wetter-than-average springs. Conversely, negative mass balance is recorded during a period warmer-than-average summers and dry springs. The cave has experienced ice mass loss since its discovery in the 1980s.

Samples of bone and teeth from the Middle Paleolithic open-air site of Rozhok I, located on the Gulf of Taganrog, were dated by radiocarbon (14C). We obtained 26 accelerator mass spectrometry (AMS) dates on a large sample of nonhuman bone and teeth recovered by N. D. Praslov during 1961–1962 from 5 of the 6 occupation horizons at Rozhok I. Two rigorous pretreatment methods were applied to the samples: ultra-filtration and XAD resin. The 14C ages from the uppermost two layers (Horizons 1 and 2) are infinite with the exception of one age near the limit of the 14C method. By contrast, the dates from Horizon 3 and the two lowermost layers (Horizons 5 and 6) are all finite ages and some are less than 45,000 BP (uncalibrated). While there is evidence of some post-depositional disturbance, there is no evidence of a stratigraphic reversal of the cultural layers. The simplest explanation for the pattern is that bones and teeth in the lower layers have been contaminated by groundwater containing young carbon. We conclude that Rozhok I probably antedates 50,000 cal BP and is beyond the range of 14C dating.

This paper presents 66 radiocarbon (14C) dates obtained at 33 key sites from the Polish part of the European Sand Belt. These calibrated dating results were compared to 34 high-resolution 14C dates obtained from a fluvial-aeolian sediments to identify pedogenic phases from the late Pleniglacial interval to the early Holocene. These identified pedogenic phases were correlated with Greenland ice-core records, revealing high sensitivity of the fluvio-aeolian paleoenvironment to climate changes. Two pedogenic phases were identified from the late Pleniglacial interval (Greenland Stadial GS-2.1b and GS-2.1a), three from the Bølling-Allerød interstadial (Greenland Stadial GI-1), one from the late Allerød–Younger Dryas boundary, and at least one from the Younger Dryas. The ages of these pedogenic phases reveal a distinct delay of 50–100 calendar years after the onset of cool climate conditions during GI-1, reflecting gradual withdrawal of vegetation. Soil horizons from the early Holocene do not show any clear relation with climate change, where breaks in soil formation were caused by local factors such as human activity.

Since the 1950s, observations of radiocarbon (14C) in tropospheric carbon dioxide (CO2) have been conducted in both hemispheres, documenting the so-called nuclear “bomb spike” and its transfer into the oceans and the terrestrial biosphere, the two compartments permanently exchanging carbon with the atmosphere. Results from the Heidelberg global network of Δ14C-CO2 observations are revisited here with respect to the insights and quantitative constraints they provided on these carbon exchange fluxes. The recent development of global and hemispheric trends of Δ14C-CO2 are further discussed in regard to their suitability to continue providing constraints for 14C-free fossil CO2 emission changes on the global and regional scale.

The present paper is an announcement of first absolute age dating directly on fossilized bones and teeth of the Pleistocene mammalian fauna from the Manjra valley, District Latur, Maharashtra, India. The fossilized samples were measured using the AMS facility at Inter-University Accelerator Centre, New Delhi, India. The results gave the time frame of 21,423 BP to 24,335 BP that correspond close to and the threshold of LGM and sheds important light on the palaeoecology of the area that supported diverse megafaunal species in the Upper Manjra valley. These calendar dates not only have wider significance in terms of first ever approximate chronological frame for the Pleistocene fauna in Peninsular India but also offer methodological innovations especially when the adequate bioapatite is absent in the fossilized bones and teeth from the fossil record.

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.

Many waterflooding oil fields, injecting water into an oil-bearing reservoir for pressure maintenance, are in their middle to late stages of development. To explore the geological conditions and improve oilfield recovery of the most important well group of the Hu 136 block, located on the border areas of three provinces (Henan, Shandong, and Hebei), Zhongyuan Oilfield, Sinopec, central China, a 14C cross-well tracer monitoring technology was developed and applied in monitoring the development status and recognize the heterogeneity of oil reservoirs. The tracer response in the production well was tracked, and the water drive speed, swept volume of the injection fluid were obtained. Finally, the reservoir heterogeneity characteristics, such as the dilution coefficient, porosity, permeability, and average pore-throat radius, were fitted according to the mathematical model of the heterogeneous multi-layer inter-well theory. The 14C-AMS technique developed in this work is expected to be a potential analytical method for evaluating underground reservoir characteristics and providing crucial scientific guidance for the mid to late oil field recovery process.

The recently formed Batagay mega-thaw slump exposes permafrost deposits to a depth of up to 92 m below ground surface and provides insight into the climate record in the region of the most severe continental climate in the Northern Hemisphere. Radiocarbon and stable isotope data were obtained to verify the age of ice wedges in the Batagay yedoma (upper Ice Complex in the local cryostratigraphy), and to deduce paleoclimate information. A millennial-scale resolution paleotemperature record from radiocarbon-dated ice wedges spans Marine Isotope Stages (MIS) 3–2. The Batagay mean January air paleo-temperature during the 44.9–42 and 30.8–27.1 cal ka BP periods was stable cold has been reconstructed to about –51 ± 3°C each.

Nine burials from Tunnug 1 site in Tuva Republic, which contained human and animal bones as well as remains of wood, were chosen for intercomparison study of preparation methods. Nine human bones, nine animal bones and 11 pieces of wood were prepared. Gelatin extracted from bones was purified using the UF method but the extraction from bones was modified with respect to acid and base treatment. Wood samples were treated as whole using acid-base-acid and cellulose was extracted for comparison. The results confirmed a highly consistent chronology of the sites centered at 200–400 CE, however, a few bones resulted in an offset between ages obtained by different methods. The extraction of cellulose was limited due to the poor preservation of wood. Our results highlight problems of dating poorly preserved bones and wood.