Gypsum is a common evaporate mineral in a wide variety of geological settings, especially in arid and semi-arid areas. It often precipitated from the natural brine systems with trace amounts of U and almost no Th, rendering it a potentially valuable U-Th geochronometer. However, U-Th dating of gypsum is often challenging, such as how to quickly and completely digest gypsum into solution, and avoid the re-crystallization of gypsum particles during the digestion and chromatography process. Here we present a rapid and practical method for high-precision U-Th dating of gypsum using the (NH₄)₂CO₃ exchange reaction and double-spike method by MC-ICPMS. Our developed protocol addresses these conventional challenges by using the chemical reaction between calcium sulfate and carbonate, resulting in the (NH₄)₂SO₄ solution and CaCO₃ precipitate. Then the CaCO₃ could be easily digested by diluted acid. With the solid-liquid separation, Ca²⁺ and SO₄^2- ions are also effectively separated, minimizing the recrystallization of gypsum. The (NH₄)₂CO₃ median, the gypsum/carbonate molar ratio of 1: 4, and the exchange reaction duration of 1.5 ~ 2 hours are suggested in this protocol. Since there is no gypsum U-Th dating reference materials to validate the accuracy of different approaches and ensure methods are repeatable across laboratories. We also prepared and characterized two natural gypsum U-Th dating reference materials (PXCG-1, PXCG-2) from PiXiao Cave, southwest China. Data from three different laboratories exhibit good agreement with both ²³⁸U content, δ²³⁴U, ²³⁰Th/²³⁸U activity ratio, and the ²³⁰Th ages. The ²³⁰Th ages of PXCG-1, PXCG-2 RMs proposed are 66.97 ± 0.31 ka, 260.82 ± 3.39 ka, respectively.

How to cite: Wang, X., Wang, L., Ma, Z., Duan, W., and Xiao, J.: U-Th dating of gypsum: methodology and reference materials, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6080, https://doi.org/10.5194/egusphere-egu24-6080, 2024.

The unprecedented environmental changes resulting from anthropogenic activities initiated during the Great Acceleration of the mid-20th century can be traced using radiocarbon analysis. The cosmogenic isotope ¹⁴C, which is produced in the atmosphere, is well-known as the geochronological tool applied to archives of the last 55 thousand years. However, during the last 200 years, the natural signal of ¹⁴C in the atmosphere and connected reservoirs (biosphere, ocean, soils, etc.,) has been perturbed by human activities. Two anthropogenic effects are observed: a decreasing trend observed in ¹⁴C concentration of the atmosphere (Suess effect) which has been temporarily reversed by aboveground thermonuclear tests of the 1950/60s.

The excess of the artificially produced ¹⁴C (bomb pulse) is a useful time marker for the mid-20th century and the detection of the bomb peak in natural archives has thus been proposed as a tool to locate and date the onset of a proposed new epoch, the Anthropocene [1].

Here we present the results of radiocarbon analysis conducted as a part of the research dedicated to establishing the Global boundary Stratotype Section and Point (GSSP) for the proposed Anthropocene series. The studied sites include corals (Flinders Reef, AU and Flower Garden Banks, USA)[2, 3], peat (Śnieżka peatland, PL)[4], lake sediment (Crawford Lake, CA and Searsville Lake, USA)[5, 6] and marine sediment (East Gotland Basin, Baltic Sea)[7]. The variety of records (different carbon reservoirs) required site and sample-specific treatment prior to analysis and site-specific interpretation of the measured ¹⁴C. Nevertheless, the mid-20th century bomb peak was detected at all but one of these sites (Searsville Lake)[6]. In all records, the observed onset of the ¹⁴C bomb peak always postdates 1954, the year of the first atmospheric ¹⁴C bomb increase. The specific reservoir effects and corrections will be discussed.

References

The Anthropocene Review, 2023. 10(1):

1.    Waters, C.N., et al. (Eds.), Candidate sites and other reference sections for the Global boundary Stratotype Section and Point of the Anthropocene series.  p. 3-24.

2.    Zinke, J., et al., North Flinders Reef (Coral Sea, Australia) Porites sp. corals as a candidate Global boundary Stratotype Section and Point  for the Anthropocene series.  p. 201-224.

3.    DeLong, K.L., et al., The Flower Garden Banks Siderastrea siderea coral as a candidate Global boundary Stratotype Section and Point  for the Anthropocene series. p. 225-250.

4.    Fiałkiewicz-Kozieł, B., et al., The Śnieżka peatland as a candidate for the Global boundary Stratotype Section and Point  for the Anthropocene series.  p. 288-315.

5.    McCarthy, F.M.G., et al., The varved succession of Crawford Lake, Milton, Ontario, Canada as a candidate Global boundary Stratotype Section and Point for the Anthropocene series.  p. 146-176.

6.    Stegner, M.A., et al., The Searsville Lake Site (California, USA) as a candidate Global boundary Stratotype Section and Point for the Anthropocene Series. p. 116-145.

7.    Kaiser, J., et al., The East Gotland Basin (Baltic Sea) as a candidate Global boundary Stratotype Section and Point for the Anthropocene series. p. 25-48.

How to cite: Hajdas, I., Crann, C., DeLong, K., Fiałkiewicz-Kozieł, B., Ivar Do Sul, J., Kaiser, J., McCarthy, F. M. G., Turner, S., Stenger, A., Waters, C., and Zinke, J.: 14C bomb peak and the onset of the Anthropocene, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10443, https://doi.org/10.5194/egusphere-egu24-10443, 2024.

Recent advancements in MC-ICPMS technology have significantly enhanced the application of U/Th geochronometry in both biogenic and chemically precipitated carbonate rocks of almost middle Pleistocene to upper Holocene. This burgeoning use, particularly in the study of late Pleistocene earth surface processes, underscores the need for standardized reference materials with a broad age spectrum with different uranium and thorium concentrations. Addressing this need, our study evaluates speleothem specimens, Gol-e-Zard Cave Standard (GZS) and Bergen Speleothem Standard (BSS), as potential reference materials.

BSS-2 was processed as a homogenized powder and dissolved aliquot for U-Th dating using MC-ICP-MS analysis. We employed various digestion and ion-resin chromatography separation methods, followed by U-Th dating using MC-ICP-MS at CENIEH, University of Miami, and University of Mainz. The ion chromatography protocols yielded recovery rates ranging from 85% to over 95%. U-series analyses of powdered BSS-2 indicated uncertainties between 0.2-1.5%, attributed to variations in the Beta-factor and the specific U and Th standard bracketing procedures used across laboratories. The dissolved BSS-2 aliquots yield between 1.5-2% of uncertainty. Obtained U-Th ages were 122.8 ± 3.3 ka (University of Miami), 124.5 ± 0.3 ka (University of Mainz), and 123.9 ± 3.2 ka (CENIEH) in the powdered samples. Furthermore, in dissolved samples, the Th-ages vary between 126.9 ± 2.9 to 127.9 ± 3.1 (CENIEH & University of Miami). GZS was prepared as a dissolved standard and the Th-date results obtained from this stalagmite are 3967 ± 0.1 to 3988 ± 0.1 (University of Miami), and 3967 ± 0.1 to 4060 ± 0.4 (CENIEH).

All Th-dates required no correction as activity ratios [230Th/232Th] exceeded 500 and 150 for BSS-2 and GZS, respectively. The consistency of these preliminary results across different laboratories suggest that GZS and BSS-2 are promising reference materials for U-Series analysis of calcium carbonate.

How to cite: Hasözbek, A., Jiménez-Barredo, F., Sharifi, A., Pourmand, A., Mertz-Kraus, R., Weber, M., Scholz, D., Lauritzen, S.-E., M. Parés, J., and Constantin, S.: Assessing Gol-e-Zard Cave (GZS) and Bergen Speleothem Standards (BSS) for U/Th Geochronometry Using MC-ICP-MS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13250, https://doi.org/10.5194/egusphere-egu24-13250, 2024.

In order to correctly determine leads and lags in the climate system and compare different proxy records over long time periods, it is important to build robust chronologies that can provide the temporal foundation for paleoclimate correlations between marine, terrestrial and ice-core records. One of the main challenges for building reliable radiocarbon-based chronologies in the marine realm is to estimate the regional marine radiocarbon reservoir age correction. Estimates of the local marine reservoir effect, ΔR, during the deglaciation can be obtained by ¹⁴C-independent dating methods such as synchronization to other well-dated archives. The cosmogenic radionuclide ¹⁰Be provides such a synchronization tool. Its atmospheric production rate is globally modulated by changes in the cosmic ray flux caused by changes in solar activity and geomagnetic field strength. The resulting variations in the meteoric fallout of¹⁰Be are recorded in sediments and ice cores and can thus be used for their synchronization.

In this study we use for the first time the authigenic ¹⁰Be/⁹Be record of a Laptev Sea sediment core and synchronize it to the ¹⁰Be records from absolutely dated ice cores. Based on the resulting absolute chronology, the ΔR  was then estimated for the Laptev Sea during the deglaciation. The deglacial estimate for the benthic ΔR value for the Laptev Sea is 345±60 ¹⁴C years, corresponding to a marine reservoir age of 864±90 ¹⁴C years. We discuss the obtained ΔR in comparison to modern ΔR estimates from the literature and its consequences for the age-depth model. Our refined age-depth model can be used as a reference for the Laptev Sea and the wider Siberian regions of the Arctic Ocean.    

How to cite: Nicolas, A., Mollenhauer, G., Malter, M., Wollenburg, J., and Adolphi, F.: Refining the age-depth model of a marine sediment record in the Laptev Sea using Beryllium-10, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17301, https://doi.org/10.5194/egusphere-egu24-17301, 2024.

μGraphiline is an innovative, fully automated graphitization system designed for radiocarbon dating using accelerator mass spectrometry. This system streamlines the conversion of samples into CO₂ and subsequently into graphite. The standard configuration of μGraphiline is capable of preparing 24 targets daily, demonstrating its high throughput. It achieves a graphitization efficiency of over 95% for 1 mg graphite targets. μGraphiline also offers additional modules for stepped combustion, ramped pyrolysis, and oxidation, all of which can be operated at user-defined temperatures. Furthermore, its design ensures a low background and reproducibility, significantly enhancing the accuracy and reliability of radiocarbon measurements.

One of the notable advantages of the system is its low maintenance requirements. It operates efficiently without the need for working gasses such as helium (He), argon (Ar), oxygen (O₂), explosive hydrogen (H₂) or liquid nitrogen, which simplifies its operation and enhances safety. This feature, coupled with its modular design and high efficiency, virtually no cross-contamination between modules and samples makes μGraphiline an advanced solution for radiocarbon dating. Lastly, the system's repeatability and reliability are backed by reference materials measurements from the International Atomic Energy Agency, demonstrating good repeatability. 

This demonstrates μGraphiline's capability to deliver fast, consistent and accurate results, making it a valuable tool for various scientific and research applications.

How to cite: Tudyka, K., Kłosok, K., Jedrzejowski, M., Rakowski, A., Pawełczyk, S., Ustrzycka, A., Miłosz, S., and Kolarczyk, A.: μGraphiline: a high-throughput, low-maintenance, fully automated 14C graphitization system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18925, https://doi.org/10.5194/egusphere-egu24-18925, 2024.

U-series disequilibrium dating or more specifically ²³⁰Th/U - dating of cold-water corals is a major absolute chronological toolbox to study the evolution of coral reefs through time and to determine absolute time scales for climate proxies. Advances in multi-collector inductively coupled ion source mass spectrometry (MC-ICPMS) have continuously improved precision of Th and U isotopic measurements over the past decades thanks the development of new high ohmic resistors for Faraday cups. Consequently, isotopic measurements and absolute precision levels are in epsilon ranges for ²³⁴U/²³⁸U ratios and in the case of materials older than a few tens of thousands of years also for ²³⁰Th/²³⁸U ratios. To obtain accurate ages the corals isotope ratios need to evolve as a U series closed system and must be free of initial ²³⁰Th and non-carbonate materials. The latter being often traced using the natural most abundant ²³²Th isotope. Coral diagenesis, bio-erosion, residual ferromanganese coatings, recrystallization, and recoil displacement of U isotopes are known sources of age disturbances and U series open system behavior. Here, I want to advocate, however, that such cold-water corals can be ideal dating objects opening far reaching perspectives of marine climate science and for past ecosystem studies. Based on approx. 1200 coral ages and isotope ratios of reef-forming cold-water corals, which correspond to strict quality criteria, a perfect agreement with theoretical predictions of a closed U series system can be found. The resulting oceanic initial (²³⁴U/²³⁸U) activity ratio for the past 510 ka varies by at most 6.7 ‰ (2s) surrounding the mean of modern seawater and of all reconstructed values of 146.5 ‰ (HU1 reference material is assumed here to be in secular radioactive equilibrium). Consequently, the ²³⁴U/²³⁸U ratios may be used for dating of old cold-water corals to expand the dating range to more than 1.2 million years. Moreover, any significant deviation between closed system ²³⁴U/²³⁸U ages and ²³⁰Th/²³⁸U ages may be used to detect U series open - system behavior. Based on the combined age determination, more consistent chronologies can be derived for cold-water coral reefs beyond 350 ka and theoretically the quality of this archive has opened a path for absolutely dated marine climate proxy records since the Mid Pleistocene Transition.

How to cite: Frank, N. and the DCWC: 230Th/U and 234U/238U dating of cold-water corals: Approaching the disequilibrium theory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19089, https://doi.org/10.5194/egusphere-egu24-19089, 2024.