Simon Fahrni’s research while affiliated with University of California, Irvine and other places

The performance of a new Multi-Isotope Low-Energy AMS (MILEA) system developed in a cooperation of Ionplus AG and ETH Zurich, Switzerland for determination of 10Be, 14C, 26Al, 41Ca, 129I, and actinoids (233U and 236U) is described based on results of factory- and on-site acceptance tests carried out at the producer and customer sites, respectively. The parameters measured were transmissions from the injector to the detector, currents in the high energy part of MILEA, radioisotope/stable blank ratios or abundance sensitivity, single sample and overall sample scatter of the radioisotope/stable isotope ratios. The results achieved were competitive with larger AMS systems.

Although Accelerator Mass Spectrometry (AMS) offers unparalleled sensitivity by investigating the fate of ¹⁴C-labeled compounds within the organism, its widespread use in ADME (absorption, distribution, metabolism, excretion) studies is limited. Conventional approaches based on Liquid Scintillation Counting (LSC) are still preferred, in particular because of complexity and costs associated with AMS measurements. Progress made over the last decade towards more compact AMS systems increased the interest in a combustion-based AMS approach allowing the analysis of samples in gaseous form. Thus, a novel gas Double Trap Interface (DTI) was designed, providing high sample throughput for the analysis of biomedical samples. DTI allows the coupling of an Elemental Analyzer (EA) for sample combustion to the hybrid ion source of a MICADAS (MIni CArbon DAting System) AMS system. The performance was evaluated in two studies through the analysis of more than 1000 samples from ¹⁴C-labeled biomatrices and fractions collected after liquid chromatography (LC). The covered activity ranged from 1 to 1000 mBq/g for labeled biomatrices and from 1 to 10000 mBq/g(C) for LC fractions. The implemented routine allows automated measurements requiring less than 5 min per sample (12–13 analyses per hour) without the need for sample conversion to graphite.

As part of the ongoing effort to improve the Northern Hemisphere radiocarbon ( ¹⁴ C) calibration curve, this study investigates the period of 856 BC to 626 BC (2805–2575 yr BP) with a total of 403 single-year ¹⁴ C measurements. In this age range, IntCal13 was constructed largely from German and Irish oak as well as Californian bristlecone pine ¹⁴ C dates, with most samples measured with a 10-yr resolution. The new data presented here is the first atmospheric ¹⁴ C single-year record of the older end of the Hallstatt plateau based on an absolutely dated tree-ring chronology. The data helped reveal a major solar proton event (SPE) which caused a spike in the production rate of cosmogenic radionuclides around 2610/2609 BP. This production event is thought to have reached a magnitude similar to the 774/775 AD production event but has remained undetected due to averaging effects in the decadal calibration data. The record leading up to the 2610/2609 BP event reveals a 11-yr solar cycle with varying cyclicity. Features of the new data and the benefits of higher resolution calibration are discussed.

Radiocarbon (C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.

Sixteen taxa comprising extinct megafauna and extant species from a single asphalt deposit (Project 23, Deposit 1) at Rancho La Brea were isotopically analyzed (δ¹³C, δ¹⁵N, δ³⁴S) and ¹⁴C dated to investigate paleoecology and feeding behavior of terrestrial vertebrates in southern California during the late Pleistocene. The large majority of the ¹⁴C dates cluster between ~35 and 36 kyr BP, but a range of ages indicate this seep was active from ~30 to >43 kyr BP. Many of the Smilodon fatalis and Canis dirus as well as the Canis latrans have similar δ¹³C (~–19‰ to −18‰) and δ¹⁵N (~11‰ to 12‰) results, indicating that these predators may have consumed similar prey species and possibly competed with each other through hunting and/or scavenging. The remains of contemporary potential prey species for these three predators include juvenile Bison antiquus and Camelops hesternus, and possibly adult Paramylodon harlani and Capromeryx minor. However, the δ¹⁵N results of a single C. dirus (8.9‰) and the Panthera atrox (8.3‰) were significantly lower than the other large predators. Potential prey for this dire wolf and lion include Nothrotheriops shastensis, Equus occidentalis and possibly Mammut americanum. Many of the herbivores appear to have utilized broadly similar C3 ecological environments. However, the adult E. occidentalis had isotopic results similar to the Sylvilagus sp. and Spermophilus beecheyi that have restricted home ranges, suggesting this horse was similarly local in its distribution or consumed a similar plant food selection. The isotopic values for extant taxa (Actinemys marmorata, Crotalus sp., Mustela frenata) suggest similar dietary patterns to their modern counterparts, indicating their ecological niches have remained relatively constant. The results presented here establish a foundation for future diachronic studies to better understand how the climate of the last ~50 kyr BP impacted biodiversity and ecological communities in southern California.

Significance This study provides evidence of an enormous solar storm around 2,610 B.P. It is only the third such event reliably documented and is comparable with the strongest event detected at AD 774/775. The event of 2,610 years B.P. stands out because of its particular signature in the radionuclide data [i.e., carbon-14 ( ¹⁴ C) data alone does not allow for an unequivocal detection of the event]. It illustrates that present efforts to find such events based solely on ¹⁴ C data likely lead to an underestimated number of such potentially devastating events for our society. In addition to ¹⁴ C data, high-resolution records of beryllium-10 and chlorine-36 are crucial for reliable estimates of the occurrence rate and the properties of past solar proton events.

Aim: Although regulatory guidances require human metabolism information of drug candidates early in the development process, the human mass balance study (or hADME study), is performed relatively late. hADME studies typically involve the administration of a14C-radiolabelled drug where biological samples are measured by conventional scintillation counting analysis. Another approach is the administration of therapeutic doses containing a14C-microtracer followed by accelerator mass spectrometry (AMS) analysis, enabling hADME studies completion much earlier. Consequently, there is an opportunity to change the current drug development paradigm. Materials & methods: To evaluate the applicability of the MICADAS-cAMS method, we successfully performed: the validation of MICADAS-cAMS for radioactivity quantification in biomatrices and, a rat ADME study, where the conventional methodology was assessed against a microtracer MICADAS-cAMS approach. Results & discussion: Combustion AMS (cAMS) technology is applicable to microtracer studies. A favorable opinion from EMA to complete the hADME in a Phase I setting was received, opening the possibilities to change drug development.

By implementing a Gas Interface System (GIS), CO2 gas measurements for radiocarbon dating of small environmental samples (<100 µgC) have been established at the MICADAS (Mini Carbon Dating System) AMS instrument in Mannheim, Germany. The system performance has been optimized and tested with respect to stability and ion yield by repeated blank and standard measurements for sample sizes down to 3 µgC. The highest ¹²C⁻ low-energy (LE) ion currents, typically reaching 8–15 µA, could be achieved for a mixing ratio of 4% CO2 in Helium, resulting in relative counting errors of 1–2% for samples larger than 10 µgC and 3–7% for sample sizes below 10 µgC. The average count rate was ca. 500 counts per microgram C for OxII standard material. The blank is on the order of 35,000–40,000 radiocarbon years, which is comparable to similar systems. The complete setup thus enables reliable dating for most environmental samples (>3 µgC).

Black carbon (BC) and organic carbon (OC) aerosols are important components of fine particulate matter (PM2.5) in polluted urban environments. Quantifying the contribution of fossil fuel and biomass combustion to BC and OC concentrations is critical for developing and validating effective air quality control measures and climate change mitigation policy. We used radiocarbon (14C) to measure fossil and contemporary biomass contributions to BC and OC at three locations in Salt Lake City, Utah, USA during 2012-2014, including during winter inversion events. Aerosol filters were analyzed with the Swiss_4S thermal-optical protocol to isolate BC. We measured fraction modern (fM) of BC and total carbon in PM2.5 with accelerator mass spectrometry and derived the fM of OC using isotope mass balance. Combined with 14C information of endmember composition, our dataset of 31 14C aerosol measurements provided a baseline of the fossil and contemporary biomass components of carbonaceous aerosol. We show that fossil fuels were the dominant source of carbonaceous aerosol during winter, contributing 88% (80–98%) of BC and 58% (48–69%) of OC. While the concentration of both BC and OC increased during inversion events, the relative source contributions did not change. The sources of BC also did not vary throughout the year, while OC had a considerably higher contemporary biomass component in summer 62% (49-76%) and was more variable. Our results suggest that in order to reduce PM2.5 levels in Salt Lake City to meet national standards, a more stringent policy targeting mobile fossil fuel sources may be necessary.

Since the AD 775 and AD 994 Δ ¹⁴ C peak (henceforth M12) was first measured by Miyake et al. (2012, 2013), several possible production mechanisms for these spike have been suggested, but the work of Mekhaldi et al. (2015) shows that a very soft energy spectrum was involved, implying that a strong solar energetic particle (SEP) event (or series of events) was responsible. Here we present Δ ¹⁴ C values from AD 721–820 Sequoiadendron giganteum annual tree-ring samples from Sequoia National Park in California, USA, together with Δ ¹⁴ C in German oak from 650–670 BC. The AD 721–820 measurements confirm that a sharp Δ ¹⁴ C peak exists at AD 775, with a peak height of approximately 15‰ and show that this spike was preceded by several decades of rapidly decreasing Δ ¹⁴ C. A sharp peak is also present at 660 BC, with a peak height of about 10‰, and published data (Reimer et al. 2013) indicate that it too was preceded by a multi-decadal Δ ¹⁴ C decrease, suggesting that solar activity was very strong just prior to both Δ ¹⁴ C peaks and may be causally related. During periods of strong solar activity there is increased probability for coronal mass ejection (CME) events that can subject the Earth’s atmosphere to high fluencies of solar energetic particles (SEPs). Periods of high solar activity (such as one in October–November 2003) can also often include many large, fast CMEs increasing the probability of geomagnetic storms. In this paper we suggest that the combination of large SEP events and elevated geomagnetic activity can lead to enhanced production of ¹⁴ C and other cosmogenic isotopes by increasing the area of the atmosphere that is irradiated by high solar energetic particles.