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Radiocarbon observations (Δ14C) in dissolved inorganic carbon (DIC) of seawater provide useful information about ocean carbon cycling and ocean circulation. To deliver high-quality observations, the Laboratory of Ion Beam Physics (LIP) at ETH-Zurich developed a new simplified method allowing the rapid analysis of radiocarbon in DIC of small seawater samples, which is continually assessed by following internal quality controls. However, a comparison with externally produced 14C measurements to better establish an equivalency between methods was still missing. Here, we make the first intercomparison with the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility based on 14 duplicate seawater samples collected in 2020. We also compare with prior deep-water observations from the 1970s to 1990s. The results show a very good agreement in both comparisons. The mean Δ14C of 12 duplicate samples measured by LIP and NOSAMS were statistically identical within one sigma uncertainty while two other duplicate samples agreed within two sigma. Based on this small number of duplicate samples, LIP values appear to be slightly lower than the NOSAMS values, but more measurements will be needed for confirmation. We also comment on storage and preservation techniques used in this study, including the freezing of samples collected in foil bags., Radiocarbon, ISSN:0033-8222

The Chronos 14Carbon-Cycle Facility is a new radiocarbon laboratory at the University of New South Wales, Australia. Built around an Ionplus 200 kV MIni-CArbon DAting System (MICADAS) Accelerator Mass Spectrometer (AMS) installed in October 2019, the facility was established to address major challenges in the Earth, Environmental and Archaeological sciences. Here we report an overview of the Chronos facility, the pretreatment methods currently employed (bones, carbonates, peat, pollen, charcoal, and wood) and results of radiocarbon and stable isotope measurements undertaken on a wide range of sample types. Measurements on international standards, known-age and blank samples demonstrate the facility is capable of measuring 14C samples from the Anthropocene back to nearly 50,000 years ago. Future work will focus on improving our understanding of the Earth system and managing resources in a future warmer world.

In 2018 Pearson et al. published a new sequence of annual radiocarbon (14C) data derived from oak (Quercus sp.) trees from Northern Ireland and bristlecone pine (Pinus longaeva) from North America across the period 1700–1500 BC. The study indicated that the more highly resolved shape of an annually based calibration dataset could improve the accuracy of 14C calibration during this period. This finding had implications for the controversial dating of the eruption of Thera in the Eastern Mediterranean. To test for interlaboratory variation and improve the robustness of the annual dataset for calibration purposes, we have generated a replicate sequence from the same Irish oaks at ETH Zürich. These data are compatible with the Irish oak 14C dataset previously produced at the University of Arizona and are used (along with additional data) to examine inter-tree and interlaboratory variation in multiyear annual 14C time-series. The results raise questions about regional 14C offsets at different scales and demonstrate the potential of annually resolved 14C for refining subdecadal and larger scale features for calibration, solar reconstruction, and multiproxy synchronization., Radiocarbon, 62 (4), ISSN:0033-8222, IntCal20: Calibration Issue

The Sun provides the principal energy input into the Earth system and solar variability represents a significant external climate forcing. Although observations of solar activity (sunspots) cover only the last about 400 years, radionuclides produced by cosmic rays and stored in tree rings or ice cores serve as proxies for solar activity extending back thousands of years. However, the presence of weather-induced noise or low temporal resolution of long, precisely dated records hampers cosmogenic nuclide-based studies of short-term solar variability such as the 11-yr Schwabe cycle. Here we present a continuous, annually resolved atmospheric 14C concentration (fractionation-corrected ratio of 14CO2 to CO2) record reconstructed from absolutely dated tree rings covering nearly all of the last millennium (ad 969–1933). The high-resolution and precision 14C record reveals the presence of the Schwabe cycle over the entire time range. The record confirms the ad 993 solar energetic particle event and reveals two new candidates (ad 1052 and ad 1279), indicating that strong solar events that might be harmful to modern electronic systems probably occur more frequently than previously thought. In addition to showing decadal-scale solar variability over the last millennium, the high-temporal-resolution record of atmospheric radiocarbon also provides a useful benchmark for making radiocarbon dating more accurate over this interval. 11-year solar cycles consistently occurred throughout the last thousand years, according to a synthesis of annually resolved tree ring radiocarbon records from central Europe.

In 2018 Pearson et al. published a new sequence of annual radiocarbon (14C) data derived from oak (Quercus sp.) trees from Northern Ireland and bristlecone pine (Pinus longaeva) from North America across the period 1700–1500 BC. The study indicated that the more highly resolved shape of an annually based calibration dataset could improve the accuracy of 14C calibration during this period. This finding had implications for the controversial dating of the eruption of Thera in the Eastern Mediterranean. To test for interlaboratory variation and improve the robustness of the annual dataset for calibration purposes, we have generated a replicate sequence from the same Irish oaks at ETH Zürich. These data are compatible with the Irish oak 14C dataset previously produced at the University of Arizona and are used (along with additional data) to examine inter-tree and interlaboratory variation in multiyear annual 14C time-series. The results raise questions about regional 14C offsets at different scales and demonstrate the potential of annually resolved 14C for refining sub decadal and larger scale features for calibration, solar reconstruction, and multiproxy synchronization.

The influence of solar variability on the Earth’s climate is a major subject of interest for understanding past and predicting future climate changes. While the observational record of solar activity (e.g. sunspots) covers only the last about 400 yr, cosmogenic nuclides stored in tree rings (14C) or ice cores (10Be, 36Cl) are used as proxies for solar activity and allow solar reconstructions reaching much further back in time 1-3. Major drawbacks of cosmogenic nuclide based solar reconstructions are the presence of weather-induced noise (e.g. 10Be in ice cores) or the low temporal resolution of long precisely dated records (14C in tree rings). Here, we present a continuous, annually resolved 14C record from precisely dated tree rings covering the past about 1’000 yr (969-1933 AD) comprising almost 1’300 highest-precision 14C measurements. The annually resolved 14C record adds significantly to the radiocarbon calibration curve4, which has hitherto been based mainly on decay counting measurements. A multi box carbon cycle model is used to extract annual 14C production changes from the tree ring data. The resulting high-resolution record of 14C production is then used to reconstruct the solar modulation parameter over the last millennium. The comparison of solar modulation with global temperature provides evidence that low solar activity could have caused the temperature reduction during the Little Ice Age. The 14C record further reveals for the first time the presence of the eleven-year solar cycle over the past 1’000 yr. The amplitude of this so called Schwabe cycle is found to correlate with the general level of the solar modulation with high amplitudes during periods of strong solar modulation and vice versa. 1 Bard, E., Raisbeck, G., Yiou, F. & Jouzel, J. (2000) Solar irradiance during the last 1200 years based on cosmogenic nuclides. Tellus Series B-Chemical and Physical Meteorology 52, 985-992.2 Muscheler, R. et al. (2007) Solar activity during the last 1000 yr inferred from radionuclide records. Quaternary Science Reviews 26, 82-97.3 Usoskin, I.G. (2017) A history of solar activity over millennia, Living Rev. Sol. Phys. 14, 3.4 Reimer, P. J. et al. (2013) Intcal13 and Marine13 Radiocarbon Age Calibration Curves 0-50,000 Years Cal Bp. Radiocarbon 55, 1869-1887.

Carbon isotopic measurements in oceanic dissolved inorganic carbon (DIC) contribute to many oceanographic fields. For instance, radiocarbon (14C) has been essential to elucidate aspects related to ocean circulation, air-sea exchange, carbon cycling and biogeochemistry. Despite its importance as a tracer in oceanography, oceanic 14C has been less well studied than other tracers (e.g. CFCs) as disentangling the natural from the artificial component is not trivial. Another major limitation was the large volume seawater samples required for the decay counting of 14C. Advances in Accelerator Mass Spectrometry (AMS) allowed the reduction of the sample volume to a couple of liters, permitting to obtain spatially better resolved distributions of oceanic 14C during repeated GO-SHIP sections. Yet, methods for sample preparation were borrowed from decay counting and not optimized for AMS. Here, we present a method that we recently developed in the Laboratory of Ion Beam Physics (ETHZ) that allows the rapid (14C in small seawater samples with unprecedented precision (14C from 50 - 60 ml samples, by sparging the acidified seawater with helium gas to extract CO2. The fully automated method is controlled via a LabVIEW program that runs through all consecutive steps: catalyst preconditioning, CO2 extraction, CO2 trapping and thermal CO2 release from the trap into the reactor for graphitization, which is performed simultaneously for 7 samples. The method is optimized by introducing a Cu-Ag furnace that improves and accelerates the graphitization to less than 2 hours. As a proof of principle, we will show two sections of 14C corresponding to two recent expeditions carried out in the North Atlantic (OVIDE section) and the Fram Strait in 2018. The high precision of the results allows for the characterization of different water masses in the subpolar North Atlantic Ocean, which reflect the export of anthropogenic carbon to the abyssal waters as a result of deep-water formation in the Iceland-Scotland Overflow Water and the Denmark Strait Overflow Water. Results will be also compared to previously published oceanic Δ14C data in those regions. These studies already demonstrate the potential to use Δ14C as a powerful and cost-efficient tool to resolve oceanic circulation patterns, especially with respect to ventilation of the water column.Casacuberta, N., Castrillejo, M., Wefing, A.-M., Bollhalder, S., & Wacker, L. (2019). High Precision 14C Analysis in Small Seawater Samples. Radiocarbon, 00(00), 1–12. https://doi.org/10.1017/rdc.2019.87

A new method to extract CO2 in seawater samples for the determination of F14C has been developed in the Laboratory of Ion Beam Physics at ETH Zurich. The setup consists of an automated sampler designed to extract dissolved inorganic carbon (DIC) from 7 samples in a row, by flushing the seawater with He gas to extract CO2. The fully automated method is controlled via a LabVIEW program that runs through all consecutive steps: catalyst preconditioning, CO2 extraction, CO2 trapping, thermal CO2 release from the trap into the reactor and finally the graphitization reaction which is performed simultaneously in the 7 reactors. The method was optimized by introducing a Cu-Ag furnace that was placed between the water and zeolite traps, which resulted in a better and faster graphitization performance (14C) as water mass tracer.

The New Oxalic Acid standard (NOX) was introduced in 1980 to replace the primarily Oxalic Acid (OX) standard, which was calibrated against OX utilizing decay counting measurements. However today, most radiocarbon measurements are performed with accelerator mass spectrometry that is more powerful as significantly less material is required and the measurement time is reduced. Here we give an update on the calibration of the NOX against OX. Over 500 radiocarbon measurements on either OX or NOX were compiled to an exact calibration, that outperforms the original calibration in precision. Our measurements are in agreement with the first measurements performed in the 80’s, demonstrating that AMS is capable of reproducing highest precision radiocarbon measurements on a routine basis.

Observations of the temporal trend in concentrations of Chernobyl radionuclides in atmospheric, terrestrial, and aquatic reservoirs near Duebendorf (Zurich) aided in quantifying fluxes and transfer velocities from one reservoir to another. Radionuclide dry and wet deposition rates and velocities from the atmosphere, washout from the catchment basins into surface waters, and deposition rates and mechanisms in lakes were determined. The results from these studies were compared to those from earlier observations on the fate of the radionuclides released by bomb tests, from reactor accidents, and from the purposeful tracer experiments in lakes. The results from our observations indicate the extent to which the Chernobyl radionuclides trace the movement of other atmospheric trace contaminants in the environment.

Radionuclide fallout from the burning Chernobyl reactor provided a pulsed input of {sup 137}Cs to surface waters and watersheds of Europe. Radionuclide analyses of surface waters indicated that initial rates of decrease of {sup 137}Cs concentrations in contaminated rivers were on the order of 0.125 day{sup {minus}1}, which was found to be consistent with the size of the mobile inventory in the watersheds (i.e., {approximately}1% of total) and with the initial dilution rate (i.e., {approximately} 0.5 m{sup {minus}1}) in river water. Analysis of {sup 134}Cs and {sup 137}Cs in waters from five different lakes in Switzerland and of settling particles collected in sediment traps from one of the lakes, Lake Zurich, revealed relatively fast whole-lake removal rates. Residence times of {sup 137}Cs in the five study lakes ranged from 5 to 21 months. Horizontal boundaries in this lake appeared to have acted first as sinks of Chernobyl {sup 137}Cs from the upper water column and later as sources of {sup 137}Cs to deeper parts of Lake Zurich. Rates of adsorption/desorption of {sup 137}Cs associated with settling particles, when compared in subsurface waters to those of uptake/release by other processes occurring in the lake, were found to be small.

Time- and space-dependent variations in the composition of settling particles were investigated along a longitudinal transect in Lower Lake Zurich. The study was carried out during summer stratification using a two-dimensional array of sediment traps deployed in the hypolimnion. Samples of the sedimentary material were analysed for total C and total N, P, Ca, Si, Al, Fe, Mn, Mg, Na, K, and the trace elements Zr, Sr, Rb, Ti, Ba, S, Pb and Zn. The elements can be classified according to their preferences in associating with a specific carrier phase. The fluxes and composition of trapped particles were found to vary seasonally with fluctuations in the main components (organic matter, calcium carbonate, biogenic silica, manganese and iron oxides, silicates) and spatially due to the following in-lake processes: 1) increasing vertical particle transport of biomass and mineralic material in the shoreward direction, 2) lateral sediment transport, which caused sediment accumulation rates to increase with depth, leading to sediment focusing, 3) episodic and patchy events of CaCO3 precipitation in the epilimnion followed by sedimentation and lateral dispersion, and 4) formation of a patchy nepheloid layer in the slightly denser bottom waters containing more fine-grained particles in suspension. Sediment focusing by lateral pathways caused by particle transport between the southern and the northern basin of Lower Lake Zurich gave rise to post-depositional in-lake redistribution of particle-bound contaminants.