Christof Vockenhuber

We report on the development and experimental characterization of a transmission-style gas ionization detector integrated with the ion microbeam system and designed for single ion sensing. The detector operates by allowing ions to pass through a single thin silicon nitride window and a short gas ionization volume (at pressures below 10 mbar) before reaching the target, thereby minimizing pre-impact energy loss and scattering. Upgrades to the ion microprobe end-station necessary to accommodate the setup are described. Focused ion beam tests demonstrated that near 100% single ion detection confidence for MeV-energy helium and nitrogen ions can be achieved reliably, with micrometer-scale spatial resolution. Detection is facilitated by operating the charge collection in the proportional regime, and ion placement precision was evaluated by scanning the ion beam across a knife-edge, with experimental results closely matching SRIM simulations. The influence of window-induced straggling was quantified, and design limitations for extending detection into the keV energy range are discussed. The presented detection system offers a promising approach for highly sensitive, target-independent, and spatially controlled single ion delivery.

This study investigates the spatial and temporal distribution of the artificial radionuclides ¹²⁹I and ²³⁶U in the Western Mediterranean Sea, focusing on their connection to radionuclide sources and circulation dynamics. Taking advantage of unprecedented precision of accelerator mass spectrometry, both tracers were firstly investigated in 2013. Here, we examine tracer observations obtained along four stations (re-)visited during the TAlPro2022 expedition in May 2022. Distributions of both ¹²⁹I and ²³⁶U were related to water masses and clearly linked to local circulation patterns: a tracer-poor surface Atlantic inflow, a thining of the tracer minimum at intermediate depths, and a higher tracer signal in Western Mediterranean Deep Waters due to dense water formation in the Algero-Provençal basin. The comparison to 2013 tracer data indicated recent deep ventilation of the Tyrrhenian Sea, the mixing of deep waters and enhanced stratification in intermediate waters in the Algero-Provençal basin due to a temperature and salinity increase between 2013 and 2022. We estimate an overall ¹²⁹I increase of 20% at all depths between 0 and 500m with respect to 2013, which is not accompanied by ²³⁶U. This suggests either the lateral transport of ¹²⁹I from the Eastern Mediterranean Sea, or an additional source of this tracer. The inventories of ¹²⁹I calculated for each water mass at the four stations point to the deposition of airborne releases from the nuclear reprocessing plants (La Hague and Sellafield) on the surface Mediterranean waters as the more likely explanation for the ¹²⁹I increase. This work demonstrates the great potential of including measurements of anthropogenic radionuclides as tracers of ocean circulation. However, a refinement of the anthropogenic inputs is necessary to improve their use in understanding ventilation changes in the Mediterranean Sea.

Barhal Valley belongs to the Çoruh Valley System in the Kaçkar Mountains of northeastern Anatolia. This 13 km long valley is located to the south of the main weather divide and to the east of Mt. Kaçkar, with the highest peak of the mountain range being 3932 m. Today, source of an average yearly precipitation of 2000 mm of moisture is the Black Sea, situated approximately 40 km to the north of the study site. Glaciers of the Last Glacial Maximum (LGM) descended directly from Mt. Kaçkar and reached an altitude of ca. 1850 m a.s.l. (above sea level). In this study, we are exploring whether the position of Barhal Valley to the south of the main weather divide and its east–west orientation have an influence on the existence and expansion of paleoglaciers. Here, we present 32 new cosmogenic ³⁶Cl dates on erratic boulders from the Çoruh Valley System. We reconstructed three geomorphologically well-contained glacier advances in the Barhal Valley, namely at 34.0 ± 2.3 ka, 22.2 ± 2.6 ka, and 18.3 ± 1.7 ka within the time window of the global LGM. Field evidence shows that the glacier of the 18.3 ± 1.7 ka advance disappeared rapidly and that by the latest time, at 15.6 ± 1.8 ka, the upper cirques were ice-free. No evidence for Lateglacial glacier fluctuations was found, and the Neoglacial activity is restricted to the cirques with rock glaciers. A range of 2700 to 3000 m for the Equilibrium Line Altitude (ELA) at the LGM was reported based on modeling of the glacial morphology. We determined that the most likely position of the LGM ELA in the Çoruh Valley System was at 2900 m a.s.l. We suggest an alternative moisture source to the direct transport from the Black Sea for the ice accumulation in the Eastern Black See Mountains. The shift of the Polar Front and of the Siberian High Pressure System to the south during the LGM resulted in the domination of easterly airflow to the Caucasus and Kaçkar Mountains with moisture from expanded lakes in central–western Siberia and from the enlarged Aral- and Caspian Seas.

Previous research suggested that the Alpine glaciers of the Northern Swiss Foreland reached their maximum extensive position during the Middle Pleistocene. Relict tills and glaciofluvial deposits, attributed to the Most Extensive Glaciation (MEG), have been found only beyond the extents of the Last Glacial Maximum (LGM). Traditionally, these sediments have been correlated to the Riss glaciation sensu Penck and Brückner and have been morphostratigraphically classified as the Higher Terrace (HT) deposits. The age of the MEG glaciation was originally proposed to be intermediate to the Brunhes/Matuyama transition (780 ka) and the Marine Isotope Stage 6 (191 ka). In this study, we focused on the glacial deposits in Möhlin (Canton of Aargau, Switzerland), in order to constrain the age of the MEG. The sediments from these deposits were analyzed to determine the provenance and depositional environments. We applied isochron-burial dating, with cosmogenic ¹⁰Be and ²⁶Al, to the till layer in the Bünten gravel pit near Möhlin. Our results indicate that a glacier of Alpine origin reached its most extensive position during the Middle Pleistocene (500 ± 100 ka). The age of the MEG thus appears to be synchronous with the most extensive glaciations in the northern hemisphere.

We applied a multi-method approach to reconstruct the Gorte rock avalanche (85–95 Mm³) located at the northeastern end of Lake Garda. The combination of field mapping, characterization of bedrock discontinuities, Dan3D-Flex runout modeling and dating of boulders with cosmogenic ³⁶Cl supports the conclusion that the deposits stem from a single rock avalanche at 6.1 ± 0.8 ka. The Gorte event may have triggered the Spiaz de Navesele–Salto della Capra landslide (3.2 Mm³), whose deposits cover the southern end of the Gorte deposits. First-order controls on detachment were the NNE–SSW- and WNW–ESE-oriented fractures in the limestone bedrock, related to the Giudicarie and Schio-Vicenza fault systems, respectively. Dan3D-Flex runout modeling sufficiently reproduced the Gorte rock avalanche, which involved detachment and sliding of a quasi-intact block, likely along marly interbeds, followed by rapid disintegration. The frictional rheology in the source area and the turbulent frictional rheology (Voellmy) in the remaining part best replicate the observed deposit extent and thickness. Heavy precipitation that occurred at that time may have contributed to failure at Gorte. Nonetheless, its timing overlaps with the nearby (<15 km) Dosso Gardene (6630–6290 cal BP) and Marocca Principale (5.3 ± 0.9 ka) landslides, making a seismic trigger plausible.

Jan Mayen is a small volcanic island situated 550 km north of Iceland. Glacial sediments and landforms are relatively common on the island but, so far, only a few of them have been dated. In this study, we present and discuss 89 ³⁶Cl dates of primarily glacial and volcanic events on Jan Mayen. Calculations of sample exposure ages were complicated by young exposure ages, young rock formation age, and high native Cl contents, leading to updates in CRONUScalc to enable accurate exposure age calculations. The samples provide good evidence against an equilibrium assumption when subtracting background production (e.g., ³⁶Cl produced by neutron capture from fission of U or Th) for samples on young bedrock, with younger exposure ages most significantly affected. Exposure ages were calculated with a range of assumptions of bedrock formation ages appropriate for Jan Mayen, including the assumption that the rock formation age equaled the exposure age (i.e., the youngest age it could possibly have), and we found that although the effect on most of the ages was small, the calculated ages of 25 of the samples increased by more than 1 standard deviation from the age calculated assuming equilibrium background production, with a maximum deviation of 6.1 ka. Due to the very young bedrock on Jan Mayen, we consider the nonequilibrium ages to be the most reliable ages from the island and conclude that large-scale deglaciation on the south and central, lower-lying, parts of the island, started around 20 ka and lasted until ~7 ka. On northern Jan Mayen, the slopes of the 2277 m high stratovolcano Beerenberg are currently partly glaciated; however, outside of the Little Ice Age moraines, all but two samples give ages between 14 and 5.7 ka.