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The Centre for Isotope Research (CIO) at the University of Groningen has operated a radiocarbon (14C) dating laboratory for almost 70 years. In 2017, the CIO received a major upgrade, which involved the relocation of the laboratory to new purpose-built premises, and the installation of a MICADAS accelerator mass spectrometer. This period of transition provides an opportunity to update the laboratory’s routine procedures. This article addresses all of the processes and quality checks the CIO has in place for registering, tracking and pretreating samples for radiocarbon dating. Complementary updates relating to radioisotope measurement and uncertainty propagation will be provided in other forthcoming publications. Here, the intention is to relay all the practical information regarding the chemical preparation of samples, and to provide a concise explanation as to why each step is deemed necessary.
22q11.2 deletion syndrome (22q11DS), one of the most common recurrent copy number variant disorders, is associated with dopaminergic abnormalities and increased risk for psychotic disorders.
Given the elevated prevalence of substance use and dopaminergic abnormalities in non-deleted patients with psychosis, we investigated the prevalence of substance use in 22q11DS, compared with that in non-deleted patients with psychosis and matched healthy controls.
This cross-sectional study involved 434 patients with 22q11DS, 265 non-deleted patients with psychosis and 134 healthy controls. Psychiatric diagnosis, full-scale IQ and COMT Val158Met genotype were determined in the 22q11DS group. Substance use data were collected according to the Composite International Diagnostic Interview.
The prevalence of total substance use (36.9%) and substance use disorders (1.2%), and weekly amounts of alcohol and nicotine use, in patients with 22q11DS was significantly lower than in non-deleted patients with psychosis or controls. Compared with patients with 22q11DS, healthy controls were 20 times more likely to use substances in general (P < 0.001); results were also significant for alcohol and nicotine use separately. Within the 22q11DS group, there was no relationship between the prevalence of substance use and psychosis or COMT genotype. Male patients with 22q11DS were more likely to use substances than female patients with 22q11DS.
The results suggest that patients with 22q11DS are at decreased risk for substance use and substance use disorders despite the increased risk of psychotic disorders. Further research into neurobiological and environmental factors involved in substance use in 22q11DS is necessary to elucidate the mechanisms involved.
Depressive patients can present with complex and different symptom patterns in clinical care. Of these, some may report patterns that are inconsistent with typical patterns of depressive symptoms. This study aimed to evaluate the validity of person-fit statistics to identify inconsistent symptom reports and to assess the clinical usefulness of providing clinicians with person-fit score feedback during depression assessment.
Inconsistent symptom reports on the Inventory of Depressive Symptomatology Self-Report (IDS-SR) were investigated quantitatively with person-fit statistics for both intake and follow-up measurements in the Groningen University Center of Psychiatry (n = 2036). Subsequently, to investigate the causes and clinical usefulness of on-the-fly person-fit alerts, qualitative follow-up assessments were conducted with three psychiatrists about 20 of their patients that were randomly selected.
Inconsistent symptom reports at intake (12.3%) were predominantly characterized by reporting of severe symptoms (e.g. psychomotor slowing) without mild symptoms (e.g. irritability). Person-fit scores at intake and follow-up were positively correlated (r = 0.45). Qualitative interviews with psychiatrists resulted in an explanation for the inconsistent response behavior (e.g. complex comorbidity, somatic complaints, and neurological abnormalities) for 19 of 20 patients. Psychiatrists indicated that if provided directly after the assessment, a person-fit alert would have led to new insights in 60%, and be reason for discussion with the patient in 75% of the cases.
Providing clinicians with automated feedback when inconsistent symptom reports occur is informative and can be used to support clinical decision-making.
We use the upper 81 mof the record of stable isotopes of water from a 122m long ice core from Lomonosovfonna, central Spitsbergen, Svalbard, to construct an ice-core chronology and the annual accumulation rates over the icefield. the isotope cycles are counted in the ice-core record using a model that neglects short-wavelength and low-amplitude cycles. We find approximately the same number of δ18O cycles as years between known reference horizons, and assume these cycles represent annual cycles. Testing the validity of this assumption using cycles in δD shows that both records give similar numbers of cycles. Using the δ18O chronology, and decompressing the accumulation records using the Nye flow model, we calculate the annual accumulation for the ice-core site back to AD 1715. We find that the average accumulation rate from 1715 to 1950 was on average 0.30 mw.e. Accumulation rates increased about 25% during the later part of the 20th century to an average of 0.41 mw.e. for the period 1950–97. the accumulation rates show highly significant 2.1 and 21 year periodicities, which gives credibility to our time-scale.
We report on the first application of a new technique in ice-core research, based on direct absorption infrared laser spectrometry (LS), for measuring 2H, 17Oand 18O isotope ratios. the data are used to calculate the deuterium excess d (defined as δ2H– 8δ18O) for a section of the Dye-3 (south Greenland) deep ice core around the Bølling transition (14 500 BP). the precision of LS is slightly better than that of most traditional methods for deuterium, but not for the oxygen isotopes. the ability to measure δ17O is new and is used here to improve the precision of the δ18O determination. Still, the final precision for δ18O remains inferior to traditional isotope ratio mass spectrometry (IRMS). Therefore, deuterium excess was calculated from a combination of the LS and IRMS isotope determinations.
We consider a specific accumulation event that occurred in January 2002 in western Dronning Maud Land, Antarctica. Snow samples were obtained a few days after accumulation. We combine meteorological analyses and isotopic modelling to describe the isotopic composition of moisture during transport. Backward trajectories were calculated, based on European Centre for Medium-Range Weather Forecasts operational archive data so that the history of the air parcels transporting water vapour to the accumulation site could be reconstructed. This trajectory study showed that the air masses were not (super)saturated along most of the transport path, which is in contrast with assumptions in Lagrangian fractionation models and probably true for most precipitation events in Antarctica. The modelled fractionation along the trajectories was too limited to explain the measured isotopic content of the snow. It is shown that the observed isotopic composition of precipitation resulted from fractionation of initially more depleted water. This lower initial isotopic composition of water vapour might result from atmospheric mixing with more depleted air along the trajectory or from earlier condensation cycles, not captured by the trajectories. This is in accordance with isotope fields resulting from general circulation models, indicating a gradient in isotopic composition from the Equator to Antarctica.
A growing body of neuropsychological and neurobiological research shows a relationship between functioning of the prefrontal cortex and criminal and violent behaviour. The prefrontal cortex is crucial for executive functions such as inhibition, attention, working memory, set-shifting and planning. A deficit in these functions – a prefrontal deficit – may result in antisocial, impulsive or even aggressive behaviour. While several meta-analyses show large effect sizes for the relationship between a prefrontal deficit, executive dysfunction and criminality, there are few studies investigating differences in executive functions between violent and non-violent offenders. Considering the relevance of identifying risk factors for violent offending, the current study explores whether a distinction between violent and non-violent offenders can be made using an extensive neuropsychological test battery.
Male remand prisoners (N = 130) in Penitentiary Institution Amsterdam Over-Amstel were administered an extensive neuropsychological test battery (Cambridge Automated Neuropsychological Test Battery; CANTAB) measuring response inhibition, planning, attention, set-shifting, working memory and impulsivity/reward sensitivity.
Violent offenders performed significantly worse on the stop-signal task (partial correlation r = 0.205, p = 0.024), a task measuring response inhibition. No further differences were found between violent and non-violent offenders. Explorative analyses revealed a significant relationship between recidivism and planning (partial correlation r = −0.209, p = 0.016).
Violent offenders show worse response inhibition compared to non-violent offenders, suggesting a more pronounced prefrontal deficit in violent offenders than in non-violent offenders.
Combining atmospheric Δ14CO2 data sets from different networks or laboratories requires secure knowledge on their compatibility. In the present study, we compare Δ14CO2 results from the Heidelberg low-level counting (LLC) laboratory to 12 international accelerator mass spectrometry (AMS) laboratories using distributed aliquots of five pure CO2 samples. The averaged result of the LLC laboratory has a measurement bias of –0.3±0.5‰ with respect to the consensus value of the AMS laboratories for the investigated atmospheric Δ14C range of 9.6 to 40.4‰. Thus, the LLC measurements on average are not significantly different from the AMS laboratories, and the most likely measurement bias is smaller than the World Meteorological Organization (WMO) interlaboratory compatibility goal for Δ14CO2 of 0.5‰. The number of intercomparison samples was, however, too small to determine whether the measurement biases of the individual AMS laboratories fulfilled the WMO goal.
In search of empirical classifications of depression and anxiety, most subtyping studies focus solely on symptoms and do so within a single disorder. This study aimed to identify and validate cross-diagnostic subtypes by simultaneously considering symptoms of depression and anxiety, and disability measures.
A large cohort of adults (Lifelines, n = 73 403) had a full assessment of 16 symptoms of mood and anxiety disorders, and measurement of physical, social and occupational disability. The best-fitting subtyping model was identified by comparing different hybrid mixture models with and without disability covariates on fit criteria in an independent test sample. The best model's classes were compared across a range of external variables.
The best-fitting Mixed Measurement Item Response Theory model with disability covariates identified five classes. Accounting for disability improved differentiation between people reporting isolated non-specific symptoms [‘Somatic’ (13.0%), and ‘Worried’ (14.0%)] and psychopathological symptoms [‘Subclinical’ (8.8%), and ‘Clinical’ (3.3%)]. Classes showed distinct associations with clinically relevant external variables [e.g. somatization: odds ratio (OR) 8.1–12.3, and chronic stress: OR 3.7–4.4]. The Subclinical class reported symptomatology at subthreshold levels while experiencing disability. No pure depression or anxiety, but only mixed classes were found.
An empirical classification model, incorporating both symptoms and disability identified clearly distinct cross-diagnostic subtypes, indicating that diagnostic nets should be cast wider than current phenomenology-based categorical systems.
This study investigates the accuracy of the radiocarbon-based calculation of the biogenic carbon fraction for different biogas and biofossil gas mixtures. The focus is on the uncertainty in the 14C reference values for 100% biogenic carbon and on the 13C-based isotope fractionation correction of the measured 14C values. The separately (AMS) measured CO2 and CH4 fractions of 8 different biogas samples showed 14C values between 102‰ and 116% (pMC). The δ13C values of these samples varied between –6‰ and +31‰ for the CO2 fraction and between –28‰ and –62‰ for the CH4 fraction. The uncertainty in calculated biogenic carbon fractions due to uncertainty in the 14C reference values depends on the available information about the origin of the used biogenic materials. It varies between ±0.5% and ±3.5% (absolute) depending on the type of biogas. A method is proposed to minimize this uncertainty for different groups of biogases. The calculated biogenic carbon fraction deviates up to ±2.5% for biofossil gas mixtures, if the applied isotope fractionation correction is based on the δ13C value of the mixed biofossil sample instead of the biogenic δ13C value. Combination of both error sources shows that the uncertainty in the calculated biogenic carbon fraction varies between ±0.7% and ±4.5%, depending on the type of biogas in the sample.
This article presents a set of Late Pleistocene marine mollusk radiocarbon (AMS) age estimates of 30–50 14C kyr BP, whereas a MIS5 age (>75 ka) is indicated by quartz and feldspar OSL dating, biostratigraphy, U-Th dating, and age-depth relationships with sea level. These results indicate that the 14C dates represent minimum ages. The age discrepancy suggests that the shells are contaminated by younger carbon following shell death. The enigmatic 14C dates cannot be “solved” by removing part of the shell by stepwise dissolution. SEM analysis of the Late Pleistocene shells within a context of geologically younger (recent/modern, Holocene) and older (Pliocene) shells shows the presence of considerable amounts of an intracrystalline secondary carbonate precipitate. The presence of this precipitate is not visible using XRD since it is of the same (aragonitic) polymorph as the original shell carbonate. The combination of nanospherulitic-shaped carbonate crystals, typical cavities, and the presence of fatty acids leads to the conclusion that the secondary carbonate, and hence the addition of younger carbon, has a bacterial origin. As shell material was studied, this study recommends an assessment of possible bacterial imprints in other materials like bone collagen as well.
In this paper, we investigate how to achieve high-accuracy radiocarbon measurements by accelerator mass spectrometry (AMS) and present measurement series (performed on archived CO2) of 14CO2 between 1985 and 1991 for Point Barrow (Alaska) and the South Pole. We report in detail the measurement plan, the error sources, and the calibration scheme that enabled us to reach a combined uncertainty of better than ±3%. The δ13C correction and a suggestion for a span (or 2-point) calibration for the 14C scale are discussed in detail. In addition, we report new, accurate values for the calibration and reference materials Ox2 and IAEA-C6 with respect to Oxl. The atmospheric 14CO2 records (1985–1991) are presented as well and are compared with other existing records for that period. The Point Barrow record agrees very well with the existing Fruholmen (northern Norway) record from the same latitude. The South Pole record shows a small seasonal cycle but with an extreme phase with a maximum on January 1st (±13 days). Together with its generally elevated 14C level compared to the Neumayer record (coastal Antarctica), this makes our South Pole data set a valuable additional source of information for global carbon cycle modeling using 14CO2 as a constraint.
We investigated sample dilution as a technique for accelerator mass spectrometry (AMS) radiocarbon analysis of very small samples (down to 30 μg). By diluting such samples up to a total weight of 200 μg, we can still perform reliable AMS measurements and improve the success rate significantly for targets that are difficult to measure. A disadvantage of this dilution technique is a loss of measurement precision. In addition, calculations of the 14C/12C isotope ratios and the uncertainties therein are not straightforward because of peculiarities in isotope fractionation processes in the AMS system. Therefore, to make sample dilution a routine method in our laboratory, we did extensive theoretical and experimental research to find the optimum conditions for all relevant parameters. Here, we report on the first detailed study dealing with all aspects of sample dilution. Our results can be applied in general. As an illustrative test case, we analyze 14C data for CO2 extracted from an ice core, from which samples of 35 μg C or less are available.
In Groningen, all organic samples for accelerator mass spectrometry (AMS) are combusted in an automatic Elemental Analyzer, coupled to an Isotope Ratio Mass Spectrometer and Cryogenic Trapping System. The Gas Chromatographic (GC) column, part of the Elemental Analyzer system, appeared to be the main cause for memory effects. Therefore we modified the Elemental Analyzer, such that the trapped CO2 no longer passed the GC column. Our system modification reduced the memory effect significantly, as shown by lower radiocarbon concentration values for anthracite backgrounds, and a much smaller spread in these values. Our modified system can perform up to 40 combustions unattended in about 6 hr.
We present the results of the 14CO2 atmospheric monitoring station at the Smilde observation station, near Groningen, the Netherlands, a typical continental station. We compared these data, for absolute values and annual variation, with data from Fruholmen, Nordkapp, Norway and Izaña, Tenerife, Canary Islands, which are situated in areas less influenced by fossil-fuel CO2. The 20-yr Smilde record shows much seasonal variation (peak-to-trough variation is ∼30‰ in contrast to ∼12‰ for Fruholmen, and ∼5‰ for Izaña) and a lower overall value due to fossil-fuel consumption, in accordance with findings from similar stations in continental Western Europe. The Fruholmen and Izaña data show fairly equal mean Δ14C levels, but differ in seasonal amplitude. This difference could be due partly to the elevation difference between the stations. The Izaña station also has a slow exchange with the ground-level air because of an inversion layer. It is speculative whether annual injection of 14C from the stratosphere also plays a role. We give the Groningen long record of tritium in precipitation, showing profound seasonality.
Atmospheric Δ14CO2 measurements are useful to investigate the regional signals of anthropogenic CO2 emissions, despite the currently scarce observational network for Δ14CO2. Plant samples are an easily attainable alternative, which have been shown to work well as a qualitative measure of the atmospheric Δ14CO2 signals integrated over the time a plant has grown. Here, we present the 14C analysis results for 89 individual maize (Zea mays) plant samples from 51 different locations that were gathered in the Netherlands in the years 2010 to 2012, and from western Germany and France in 2012. We describe our sampling strategy and results, and include a comparison to a model simulation of the Δ14CO2 that would be accumulated in each plant over a growing season. Our model simulates the Δ14CO2 signatures in good agreement with observed plant samples, resulting in a root-mean-square deviation (RMSD) of 3.30‰. This value is comparable to the measurement uncertainty, but still relatively large (20–50%) compared to the total signal. It is also comparable to the spread in Δ14CO2 values found across multiple plants from a single site, and to the spread found when averaging across larger regions. We nevertheless find that both measurements and model capture the large-scale (>100 km) regional Δ14CO2 gradients, with significant observation-model correlations in all three countries in which we collected samples. The modeled plant results suggest that the largest gradients found in the Netherlands and Germany are associated with emissions from energy production and road traffic, while in France, the 14CO2 enrichment from nuclear sources dominates in many samples. Overall, the required model-based interpretation of plant samples adds additional uncertainty to the already relatively large measurement uncertainty in Δ14CO2, and we suggest that future fossil fuel monitoring efforts should prioritize other strategies such as direct atmospheric sampling of CO2 and Δ14CO2.
The Amsterdam glacial basin was a major sedimentary sink from late Saalian until late Eemian (Picea zone, E6) times. The basin’s exemplary record makes it a potential reference area for the last interglacial stage. The cored Amsterdam-Terminal borehole was drilled in 1997 to provide a record throughout the Eemian interglacial. Integrated facies analysis has resulted in a detailed reconstruction of the sedimentary history.
After the Saalian ice mass had disappeared from the area, a large, deep lake had come into being, fed by the Rhine river. At the end of the glacial, the lake became smaller because it was cut off from the river-water supply, and eventually only a number of shallow pools remained in the Amsterdam basin. During the early Eemian (Betula zone, El), a seepage lake existed at the site. The lake deepened under the influence of a steadily rising sea level and finally evolved into a silled lagoon (late Quercus zone, E3). Initially, the lagoon water had fairly stable stratification, but as the sea level continued to rise the sill lost its significance, the lagoon becoming well mixed by the middle of the Corylus/Taxus zone (E4b). The phase of free exchange with the open sea ended in the early Carpinus zone (E5), when barriers developed in the sill area causing the lagoon to become stratified again. During the Late Eemian (late E5), a more dynamic system developed. The sandy barriers that had obstructed exchange with the open sea were no longer effective, and a tidally-influenced coastal lagoon formed.
The Eemian sedimentary history shown in the Amsterdam-Terminal borehole is intimately connected with the sea-level history. Because the site includes both a high-resolution pollen signal and a record of sea-level change, it has potential for correlation on various scales. Palaeomagnetic results show that the sediments predate the Blake Event, which confirms that this reversal excursion is relatively young. The U/Th age of the uppermost part of the Eemian sequence is 118.2±6.3 ka.
Accelerator mass spectrometry (AMS) measurements of the radiocarbon content in very old samples are often challenging and carry large relative uncertainties due to possible contaminations acquired during the preparation and storage steps. In case of such old samples, the natural surrounding levels of 14C from gases in the atmosphere, which may well be the source of contamination among others, are 2–3 orders of magnitude higher than the samples themselves. Hence, serious efforts are taken during the preparation steps to have the samples pristine until measurements are performed. As samples often have to be temporarily stored until AMS measurements can be performed, storage conditions also become extremely crucial. Here we describe an assessment of this process of contamination in background AMS samples. Samples, both as pressed graphite (on AMS targets) and graphite powder, were stored in various storage conditions (CO2-spiked air) to investigate the extent of contamination. The experiments clearly show that the pressed targets are more vulnerable to contamination than the unpressed graphite. Experiments conducted with enriched CO2-spiked laboratory air also reveal that the contaminating carbon is not only limited to the target surface but also penetrates into the matrix. A combination of measurements on understanding the chemical nature of the graphitization product, combined with long-available knowledge on “adventitious carbon” from the surface science community, brought us to the conclusion that contamination is to a certain extent inevitable. However, it can be minimized, and should be dealt with by sputter-cleaning the samples individually before the actual measurement.
This article presents results from the first 3 rounds of an international intercomparison of measurements of Δ14CO2 in liter-scale samples of whole air by groups using accelerator mass spectrometry (AMS). The ultimate goal of the intercomparison is to allow the merging of Δ14CO2 data from different groups, with the confidence that differences in the data are geophysical gradients and not artifacts of calibration. Eight groups have participated in at least 1 round of the intercomparison, which has so far included 3 rounds of air distribution between 2007 and 2010. The comparison is intended to be ongoing, so that: a) the community obtains a regular assessment of differences between laboratories; and b) individual laboratories can begin to assess the long-term repeatability of their measurements of the same source air. Air used in the intercomparison was compressed into 2 high-pressure cylinders in 2005 and 2006 at Niwot Ridge, Colorado (USA), with one of the tanks “spiked” with fossil CO2, so that the 2 tanks span the range of Δ14CO2 typically encountered when measuring air from both remote background locations and polluted urban ones. Three groups show interlaboratory comparability within l% for ambient level Δ14CO2. For high CO2/low Δ14CO2 air, 4 laboratories showed comparability within 2%. This approaches the goals set out by the World Meteorological Organization (WMO) CO2 Measurements Experts Group in 2005. One important observation is that single-sample precisions typically reported by the AMS community cannot always explain the observed differences within and between laboratories. This emphasizes the need to use long-term repeatability as a metric for measurement precision, especially in the context of long-term atmospheric monitoring.