CL5.2 | Radiocarbon and other geochronological tools for environmental reconstructions - technical advances and novel applications
Radiocarbon and other geochronological tools for environmental reconstructions - technical advances and novel applications
Co-organized by AS5/BG2, co-sponsored by PAGES
Convener: Franziska Lechleitner | Co-conveners: Negar Haghipour, Gina E. Moseley, Andreas Lang, Arne Ramisch, Irka Hajdas, Gesine Mollenhauer
Orals
| Tue, 25 Apr, 10:45–12:30 (CEST)
 
Room 0.49/50
Posters on site
| Attendance Tue, 25 Apr, 16:15–18:00 (CEST)
 
Hall X5
Posters virtual
| Attendance Tue, 25 Apr, 16:15–18:00 (CEST)
 
vHall CL
Orals |
Tue, 10:45
Tue, 16:15
Tue, 16:15
The Quaternary Period (last 2.6 million years) is characterized by frequent and abrupt climate swings that were accompanied by rapid environmental change. Studying these changes requires accurate and precise dating methods that can be effectively applied to environmental archives. A range of different methods or a combination of various dating techniques can be used, depending on the archive, time range, and research question.
Radiocarbon (14C) in particular is a key environmental tracer that can be widely applied in geochronology, environmental, and climate sciences. It is an invaluable tool to understand the global carbon cycle, as it can be used to trace the transfer of carbon between the atmosphere and other reservoirs, e.g., soils, oceans, and the geosphere, and to understand the impact of anthropogenic perturbations on these reservoirs.

With this session, we aim at bringing together an interdisciplinary group of researchers focused on dating and understanding climate archives of the Quaternary Period. Our session will focus on the application of geochronometers on one hand, as well as on the use of radiocarbon from natural reservoirs and archives that improve our understanding of the carbon cycle. In particular, we look forward to discussing (1) experimental and analytical advances (e.g. in sample preparation and measurement techniques); (2) methods that reduce, quantify and express dating uncertainties in any dating method, including high-resolution radiocarbon approaches; (3) new insights into the global carbon cycle, e.g., storage times in soils, sediment dispersal, ocean circulation, or carbon transfer between reservoirs; (4) general geochronological applications such as long-term landscape evolution, rates of geomorphological processes, and chronologies for records of climate change.

Orals: Tue, 25 Apr | Room 0.49/50

Chairpersons: Franziska Lechleitner, Negar Haghipour, Andreas Lang
10:45–10:50
Radiocarbon as a tool to understand the global carbon cycle
10:50–11:00
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EGU23-1481
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On-site presentation
Martin Butzin, Peter Köhler, Christoph Völker, Ying Ye, and Gerrit Lohmann

It has been estimated that Δ14C values of marine dissolved inorganic radiocarbon (Δ14CDIC) are primarily governed by transport and radioactive decay. This implies that Δ14CDIC can be considered as a radioconservative tracer which can be implemented into Earth system models without a full marine carbon cycle model. Here we evaluate the accuracies of the radioconservative modelling approach and of a further modelling approach which considers a different simplified representation of the marine radiocarbon cycle, presenting simulation results obtained with the ocean general circulation model FESOM and the marine biogeochemistry model REcoM. The relative uncertainties between the two simplified and the comprehensive treatments of the marine radiocarbon cycle are less than 5%. Therefore, the simplified Δ14CDIC modelling approaches should be sufficiently accurate for many marine radiocarbon studies. 

How to cite: Butzin, M., Köhler, P., Völker, C., Ye, Y., and Lohmann, G.: How accurate are marine Δ14CDIC modelling approaches?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1481, https://doi.org/10.5194/egusphere-egu23-1481, 2023.

11:00–11:10
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EGU23-2836
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ECS
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On-site presentation
Craig Smeaton, Negar Haghipour, William Austin, and Timothy Eglington

Fjords are recognised as important hotspots for the burial and storage of organic carbon (OC) within their sediment, which potentially provides a long-term climate regulation service. Annually, it is estimated that 18 Mt of OC is buried within fjord sediments with between 55 – 62% of the OC originating from the terrestrial environment. The transfer of OC from the terrestrial environment to the fjord sediments is likely a significant pathway for aged OC to reach the coastal ocean. By estimating the quantity and mapping the spatial distribution of aged OC within the fjord sediments, we can develop a better understanding of the processes that govern the transfer of terrestrial OC from the catchment to the sediment of fjords, further constraining their role in long-term climate regulation.

Here we bring together radiocarbon analysis with isotopic and biomarker measurements to investigate the age of the surficial sediments within 46 fjords across the North Atlantic. The fjords in this study range from Scottish systems with catchments dominant with OC rich peat to the glaciated systems of Svalbard and Greenland.  The results from this analysis highlight that a multiple natural and anthropogenic processes govern the quantity and distribution of aged OC across North Atlantic fjords ranging between glacial input of fossil OC to the erosion of aged terrestrial material facilitated by deforestation.  This study highlights the fundamental need to understand the processes that govern the transfer of OC across the land-ocean interface to allow the role these marine sedimentary systems play in long-term climate regulation to be constrained.    

How to cite: Smeaton, C., Haghipour, N., Austin, W., and Eglington, T.: The Role of Aged Organic Carbon in North Atlantic Fjord Sediments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2836, https://doi.org/10.5194/egusphere-egu23-2836, 2023.

11:10–11:20
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EGU23-128
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ECS
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On-site presentation
Andrea Göhring, C. Matthias Hüls, Stefan Hölzl, Christoph Mayr, and Harald Strauss

The so-called sea spray effect is known to considerably influence the stable isotope fingerprint of coastal samples (plants, soil, bones, teeth). However, the impact of sea spray on radiocarbon analyses in environmental samples from coastal sites has not been investigated, yet. Sea spray aerosols, containing, e.g., HCO3- or CO32- of marine origin, enter the terrestrial environment, shifting stable isotope values of terrestrial samples towards a seemingly marine isotope signature. Moreover, the sea spray is always accompanied by physiological effects in the sprayed plants, e.g., due to the salinity of the incorporated water, also visible in, e.g., stable carbon isotope data. A terrestrial herbivore, never consuming any marine food, can show a marine isotope signal due to the sea spray effect. While the marine reservoir effect, resulting from the consumption of marine food sources, can be investigated by calculating isotopic mixing models based on the δ13Ccollagen and δ15Ncollagen values of archaeological animal and human bones, the sea spray effect remains undetected in the δ13Ccollagen and δ15Ncollagen values of individuals consuming terrestrial protein (i.e., plant sources) influenced by marine aerosols. Therefore, it is important to investigate the influence of the sea spray on the radiocarbon signature.

The impact of either the direct or the accompanied, indirect sea spray effect can be visualized by an artificial sea spray experiment which was performed in a greenhouse. European beach grass (Ammophila arenaria, L.) was sprayed with mineral salt solution of different ion concentration but only traces of NaCl, with salty water from the Schlei inlet, collected next to the archaeological site of Haithabu (Germany), and with seawater from the Baltic Sea, collected at the western coast of Fehmarn island (Germany), respectively. Plants of all treatment groups were irrigated with Munich tap water (mainly originating from Mangfall valley). Radiocarbon analyses (F14C), stable as well as radiogenic isotope analyses (δ13CDIC, δ13Cbulk, δ13Ccellulose, δ18Ocellulose, δ18Osulfate, δ34Ssulfate, δ34Stotal S, 87Sr/86Sr), and (trace) elemental analyses were conducted on the plant, soil, and water samples (spray water, irrigation water) using mass spectrometry (AMS, IRMS, TIMS, ICP-MS, IC).

Radiocarbon analyses of the plants showed an impact due to the artificial sea spray. The indirect sea spray effect, resulting from either salinity (NaCl) or HCO3- stress, has an impact on plants’ F14C. The study demonstrates that a substantial proportion of 14C, which is taken up by the sprayed plants, originates from either irrigation or spray water. Stomatal conductance is markedly reduced due to both salinity and bicarbonate stress. Accordingly, less atmospheric 14CO2 can enter the plants via their stomata, while H14CO3-/14CO32-/14CO2 (aq.) can still be incorporated via the roots.

A multi-dimensional approach with a combined analysis of stable (δ13C, δ18O, δ34S), radiogenic (87Sr/86Sr), and radiocarbon isotopes in environmental samples allows to depict a detailed image of biochemical and physiological processes associated with the sea spray effect and will help to reveal new insights into the sea spray impact on the isotopic fingerprint of plants, animals, and humans, including potential caveats for radiocarbon analyses in coastal regions.

How to cite: Göhring, A., Hüls, C. M., Hölzl, S., Mayr, C., and Strauss, H.: Indirect sea spray effects on radiocarbon data of coastal plants – how physiological reactions in plants can be visualized by a combined investigation of stable, radiogenic, and radiocarbon isotopes in a greenhouse experiment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-128, https://doi.org/10.5194/egusphere-egu23-128, 2023.

11:20–11:30
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EGU23-11287
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ECS
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On-site presentation
Nora Gallarotti, Lisa Bröder, Julie Lattaud, Negar Haghipour, and Timothy Eglinton

Rivers are important agents in the lateral transfer of carbon from terrestrial to the marine realm, thus forming a key component of the global carbon cycle. Carbon sources and transformations along the land-ocean aquatic continuum are dynamic with a complex interplay between dissolved and particulate, and inorganic and organic carbon pools. Elucidating interrelationships between these pools is hindered by multiple sources and processes that influence the carbon signatures of these pools in a dissimilar fashion. Icelandic streams and rivers offer an opportunity to directly assess the fluvial carbon pool dynamics due to the virtual absence of sedimentary rocks (e.g., shales, carbonates with a radiocarbon dead signature) that otherwise “muddy the waters” with respect to apparent sources and turnover times.

In order to characterize carbon transport patterns of Icelandic rivers and streams, we collected water samples from 43 river systems with watersheds that cover a wide range of catchment properties such as size, water discharge, climate as well as landcover. Here we assess the concentrations as well as the isotopic composition (13C, 14C) of particulate and dissolved organic carbon (POC; DOC, respectively) as well as dissolved inorganic carbon (DIC) alongside stable water isotopes (δ2H, δ18O) and major ion geochemistry.
Radiocarbon content (reported as fraction modern; F14C) of POC, DOC and DIC show similar patterns: lower F14C values (i.e., highest radiocarbon ages) are mostly associated with glacial runoff while higher F14C values (younger carbon) correspond to higher soil organic carbon content within the respective catchment. This dataset is but a first glimpse at carbon transport patterns in Icelandic rivers. Biomarker concentrations and isotopic compositions such as leaf waxes (n-alkanes, n-alkanoic acids) and soil derived lipids (branched glycerol dialkyl glycerol tetraether) will be used to further investigate provenance, transport and storage mechanisms in the diverse suite of Icelandic catchments.

How to cite: Gallarotti, N., Bröder, L., Lattaud, J., Haghipour, N., and Eglinton, T.: 14C-based deconvolution of relationships between carbon pools in Icelandic rivers and streams, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11287, https://doi.org/10.5194/egusphere-egu23-11287, 2023.

11:30–11:40
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EGU23-8323
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ECS
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On-site presentation
Margaux Moreno Duborgel, Luisa Isabell Minich, Negar Haghipour, Beatriz González-Domíngez, Timothy Eglinton, and Frank Hagedorn

Soils are the largest carbon (C) reservoir in terrestrial ecosystems. There are still numerous uncertainties concerning the fate of soil organic carbon and its feedback on climate change. Radiocarbon is a useful approach to better understanding the carbon cycle. The nuclear weapon testing in the 1960s induced a peak in 14C atmospheric concentration – a signal that can be used to trace the incorporation and turnover of C in soil. By separating the soil in different fractions and measuring the 14C in them, we can quantify how much C and for how long is stored in soils, and where soil organic carbon is stabilised.

Our study aimed at identifying the impact of climate and mineralogy on soil organic matter turnover on a regional scale. We analysed C pools and 14C contents in the organic layer, mineral soil (0-20cm) and its fractions from 54 sites across Switzerland. These 54 sites are systematically spread across natural climatic and geological gradients and were repeatedly sampled in the 1990s and 2014. The mineral soil was incubated for 181 days and 14C was measured in the respired CO2. The mineral soil was fractionated according to density into particulate organic matter (POM) and mineral-associated organic matter (MAOM). We then oxidised the mineral-associated organic matter with hydrogen peroxide to remove its labile fraction of carbon. Our 14C dataset was analysed together with ancillary data comprising soil properties and climatic variables from the studied sites.

Our radiocarbon dataset showed that the carbon that was respired from the mineral soil originated predominantly from particulate organic matter. The bomb spike signal was incorporated in the organic layer and in the particulate organic matter, while the mineral-associated organic matter had turnover times on centennial to millennial time scales (from 94 to 3060 years). Further chemical oxidation of MAOM using hydrogen peroxide revealed a stronger depletion in radiocarbon of the residual fraction with Δ14C values ranging between -173 ‰ and -47 ‰. This indicates that the MAOM is a mixture of 14C-enriched organic matter and very old material.

With respect to the controlling factors of soil organic matter turnover time, the radiocarbon signature of the POM is most strongly affected by climatic variables such as mean annual temperatures. In contrast to POM, the mineral-associated organic matter, comprising the greatest pool of soil organic carbon is driven by chemical soil properties. For instance, older 14C ages are found in acidic soils with low pH values ranging between 3 and 4. In these soils, Al and Fe oxides concentrations are high. We showed that the concentrations of pedogenic oxides in the soil correlate with soil organic carbon concentrations in the mineral-associated organic matter. In soils with higher pH (>7), we can also find old 14C ages. In these soils, C is stabilised by interactions with calcium ions and carbonates.

Overall, our regional scale dataset shows that the net accumulation of labile soil organic matter seems to be climate sensitive, while mineralogy and weathering contribute most significantly to the stabilisation of organic carbon in the soil.

 

 

How to cite: Moreno Duborgel, M., Minich, L. I., Haghipour, N., González-Domíngez, B., Eglinton, T., and Hagedorn, F.: Using radiocarbon to identify the impact of climate and mineralogy on soil organic matter turnover, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8323, https://doi.org/10.5194/egusphere-egu23-8323, 2023.

Geochronological applications to characterize Quaternary paleoenvironments
11:40–11:50
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EGU23-4545
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On-site presentation
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Sune Olander Rasmussen, Giulia Sinnl, Anders Svensson, and Bo Møllesøe Vinther

The full potential of palaeoclimate data relies on reliable time scales, i.e., a relation tying the physical dimension of the palaeoclimate archive with age. For many records, including ice cores, identification and counting of annual layers is the most direct and accurate way to obtain a time scale provided that high-resolution measurements of parameters showing annual variability are available. Annual-layer counting can provide very precise estimates of event durations and rates of change, but as errors accumulate with age, the accuracy decreases with depth/time. In contrast, radiometric methods often have good accuracy, and in principle, the two approaches can be combined to form highly accurate and precise time scales provided that the archives and their time scales can be robustly aligned. This can be done based on e.g. volcanic markers, common and correlatable features in cosmogenic isotope records, or on climatic wriggle-matching when the possible leads and lags between records is considered.

The Central Greenland ice cores are drilled in the interior areas of the ice sheet where precipitation rates are appropriate for the formation and preservation of annual layers, thereby allowing annual layers to be identified in the Holocene period and well into the last glacial period. The Greenland Ice-Core Chronology (GICC) is an attempt to derive a consistent, common time scale for the Greenland ice cores by combining data from multiple cores, using for each time period all available annually resolved data and then applying the time scale to the other cores by means of matching patterns of volcanic eruptions and other reference horizons. In this way, data from all the ice cores can be interpreted together on a common time scale (i.e., with very small relative dating uncertainty), greatly reducing the risk of artificial offsets due to misinterpretation of individual records. The first version of GICC, named GICC05, was published in 2006 and 2008, where the dating covered the time period back to 60 ka b2k, at which point the layers had thinned too much to continue with continuous annual layer counting.

Since then, high-resolution data from the newer Greenland ice cores NEEM and EGRIP have appeared, and comparisons to other palaeoclimate records on radiometric time scales have shown that in some sections, GICC05 was not as accurate as initially estimated, motivating a revision on the time scale. The top 3.8 ka of the time scale was recently revised, leading to changes in age of 10-15 years for the section older than 2500 years (see presentation by Giulia Sinnl). Here, we review the older sections of GICC05 in the context of other well-dated palaeoclimate archives and cosmogenic isotope records, as well as model-based estimates of climate leads and lags relevant when aligning climate records, and outline a plan for how to continue the revision of GICC05.

How to cite: Rasmussen, S. O., Sinnl, G., Svensson, A., and Vinther, B. M.: Evaluating the accuracy of the Greenland Ice-Core Chronology (GICC), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4545, https://doi.org/10.5194/egusphere-egu23-4545, 2023.

11:50–12:00
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EGU23-8195
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On-site presentation
Pierre Valla, Yann Rolland, Romain Delunel, Julien Carcaillet, and Christian Crouzet

Glacial/interglacial transitions in mountainous areas are marked by significant glacier retreat from forelands to inner massifs, resulting in large-scale and ephemeral lake formation that are subsequently filled (or not) by sediment transfer during lateglacial to postglacial times. When valley paleo-infills are preserved, they form precious archives to investigate (1) Alpine erosion dynamics and paleo-environmental conditions during key transition periods from full glacial stages to interglacials, and (2) glacial erosion patterns during susbequent glaciation.

In this contribution, we investigate such sedimentary deposits (locally called as "banquettes") in the French western Alps, and more precisely along the Isère valley and Val du Bourget. Previous research have attributed these deposits to the Riss – Würm transition due to their position under a basal compact till and to the MIS 6/5 transition up to early MIS 4 from palynological constraints, although no absolute ages has been available so far. Based on existing mapping of their spatial distribution and stratigraphic reconstructions, we sampled coarse-sand and sandy-gravel layers within these deposits for constraining both sediment deposition time (OSL dating) and provenance (glacial/postglacial origin, using terrestrial cosmogenic nuclide TCN 10Be in quartz). In addition, their spatial distribution provides estimates of maximum glacial erosion during the last glacial cycle, which can be subsequently used as spatial constraints for ice model predictions.

Our results confirm deposition times of these sedimentary units at the MIS 6/5 transition, with dating constraints from the late MIS 6 (ca. 145 ka) to the early MIS 5 (Eemien, 115-130 ka) for sandy layers. Upper sandy-gravel layers have younger deposition ages of ca. 80 ka, illustrating sediment fluxes at the transition from late MIS 5 to early MIS 4. We compare this temporal sequence to more recent sediment infills of the Isère valley (14C and OSL dating) during the Lateglacial to Holocene (MIS 2/1) transition. TCN data from sand samples also illustrate the sharp transition from full glacial to interglacial conditions, with a significant increase in 10Be concentrations from Lateglacial to post-glacial sediments. We propose that the observed signal can reflect changes in erosion rates, but also in glacier expansion or in paleo-environmental conditions, with export of stored subglacial sediments as well as the re-establishment of sediment/soil production and transfer along the catchment routing system following glacier retreat.

How to cite: Valla, P., Rolland, Y., Delunel, R., Carcaillet, J., and Crouzet, C.: Lateglacial to interglacial sediment infills in Alpine valleys: timing, sediment provenance and paleo-environmental conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8195, https://doi.org/10.5194/egusphere-egu23-8195, 2023.

12:00–12:10
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EGU23-9064
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ECS
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On-site presentation
Francisco Hevia-Cruz, Anthony Hildenbrand, Nathan D. Sheldon, François Chabaux, Fernando O. Marques, Julie Carlut, and Vittorio Zanon

Paleosols (PSs) contain valuable information about the climatic conditions under which they formed and constitute an outstanding archive of past weathering processes. Nevertheless, paleosol dating over most of the Quaternary remains challenging. Volcanic environments are unique sites for such purposes, as precise radiometric age determination can be achieved on volcanic units ‘bracketing’ PSs. Here, we present a combined geochemical and geochronological study of PSs spanning the last Myr in the Central Azores archipelago (Pico, Faial and São Jorge Islands; central North Atlantic). Precise K-Ar dating of lava flows on groundmass separates (unspiked Cassignol-Gillot technique) yield ages with a typical uncertainty of a few kyr, allowing us to tightly constrain PS ages and weathering rates near key paleoclimatic transitions. PS geochemistry further allowed us to reconstruct weathering conditions and estimate Mean Annual Precipitation and Temperature (MAP & MAT) by two proxies previously validated for other volcanic terranes (CIA-K and Clayeyness).

Four periods of PSs formation are constrained at 870-845 ka, ~725 ka, 320-280 ka and 130-45 ka. Most PSs formed just after interglacial peaks, with a few exceptions. Our MAP reconstructions are variable (600-1,500 mm/yr), but generally lower than current annual precipitations (~1,000 mm/yr). MAT estimates (14-28°C) are higher than present-day annual temperatures (~17.5°C). MAP & MAT variations are in general agreement with global climatic curves; the highest values (28°C, 1,500 mm/yr) are reached at ~855 ka, coinciding with an interglacial peak. The younger PSs (130-45 ka) indicate more stable MAP & MAT in the ranges 650-1,000 mm/yr and 15-20°C, respectively and seem to show a temperature decrease after the MIS5e interglacial stage.

Most paleosols were formed in a few kyr under high MAT (>17°C) and moderate to high MAP (>700 mm/yr), supporting a major influence of temperature on weathering kinetics. Parental material texture also had an important role, as several PSs formed upon pyroclastic deposits over most of their depth, whereas those developed on lava flows were generally restricted to the highly fragmented upper brecciated parts. Minimum vertical soil formation rates are in the range of ~0.3-4.5 cm/kyr, with a mean of ~1.7 cm/kyr and an outlier around ~10 cm/kyr. Those generally high values can be explained by the highly vesicular parental material, and by an exceptionally feldspar-rich (easily weathered) parental rock for the outlier.

As current precipitation and temperatures are higher than the threshold values of ~700 mm/yr and ~17°C under which most PSs formed, enhanced soil formation is expected for the near future, especially in the context of global warming and particularly in volcanic contexts. This may have important and fast impacts on local human activities, but also regarding CO2 consumption by rock weathering and geological hazards.

How to cite: Hevia-Cruz, F., Hildenbrand, A., Sheldon, N. D., Chabaux, F., Marques, F. O., Carlut, J., and Zanon, V.: Paleoclimate and weathering on volcanic islands: insights from well-dated paleosols spanning the last Myr in the Central Azores, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9064, https://doi.org/10.5194/egusphere-egu23-9064, 2023.

Technical advancements in Quaternary geochronology
12:10–12:20
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EGU23-8033
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ECS
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On-site presentation
Alex Houston, William Austin, and Mark Garnett

The surficial 10 cm of Scotland’s saltmarshes are estimated to store 1.35 ± 0.33 Mt CO2 equivalent, approximately 3.37% of Scotland’s national greenhouse gas emissions in 20201,2. This is largely achieved through effective preservation of organic matter (OM) in low oxygen, sulphidic soils1. Saltmarshes gain organic carbon (OC) through in-situ (autochthonous) production by vegetation and benthic microalgae, and the accumulation of marine and terrestrial material during tidal inundation (allochthonous)3.

A key blue carbon challenge is to empirically understand, under current and predicted warmer conditions, the sources of OC accreted into and respired from saltmarshes. This can determine the proportion of the total OC pool which is additional through in-situ sequestration or from increased preservation of allochthonous OM3. Alongside 13C and 15N isotopes, radiocarbon (14C) analysis/dating can be used to determine the sources of saltmarsh surficial soil OC4.

We hypothesise that at ambient temperatures the younger and more labile, and predominantly autochthonous OM, will be preferentially decomposed.  But at elevated temperatures the aged, and predominantly allochthonous, OM pool will increasingly contribute to the respired greenhouse gases.

To test this hypothesis, we collected soil cores and surficial sediment samples from three contrasting Scottish saltmarshes. We analysed them for 14C to gain an understanding of the age and sources of the autochthonous and allochthonous OM accumulating. We also aerobically incubated sub-samples of the soil in temperature-controlled experiments at 11.1 ± 1°C (ambient) and 20 ± 1°C (elevated). The evolved CO2 was collected on molecular sieve traps and analysed for 14C content/age.

Our results will facilitate comparison of the age of the bulk OM and the respired CO2 to the thermogravimetrically measured reactivity of the OM determined using the recently developed Carbon Reactivity Index5. We will present our findings and introduce our ongoing work on anaerobic incubations of the same soils, which includes the novel measurement of the evolved 14CH4.

Our research contributes to a growing evidence base for emissions from saltmarshes, and the sources of OC accreting in their soils, which is vital for understanding how they cycle carbon and their ability to mitigate climate change. It will contribute to the creation of saltmarsh carbon cycle models and inform work to include saltmarshes in the UK’s Nationally Determined Contributions.

References

  • Smeaton C, Burden A, Ruranska P, et al. Using citizen science to estimate surficial soil Blue Carbon stocks in Great British saltmarshes. Front Mar Sci. 2022;9. Accessed November 28, 2022. https://www.frontiersin.org/articles/10.3389/fmars.2022.959459
  • Scottish Goverment. Scottish Greenhouse Gas Statistics 2020.; 2022. https://www.gov.scot/publications/scottish-greenhouse-gas-statistics-2020/
  • McTigue ND, Walker QA, Currin CA. Refining Estimates of Greenhouse Gas Emissions From Salt Marsh “Blue Carbon” Erosion and Decomposition. Front Mar Sci. 2021;8. Accessed January 26, 2022. https://www.frontiersin.org/article/10.3389/fmars.2021.661442
  • Hajdas I, Ascough P, Garnett MH, et al. Radiocarbon dating. Nat Rev Methods Primer. 2021;1(1):1-26. doi:10.1038/s43586-021-00058-7
  • Smeaton C, Austin WEN. Quality Not Quantity: Prioritizing the Management of Sedimentary Organic Matter Across Continental Shelf Seas. Geophys Res Lett. 2022;49(5):e2021GL097481. doi:10.1029/2021GL097481

How to cite: Houston, A., Austin, W., and Garnett, M.: A Novel Method for Radiocarbon Dating Greenhouse Gas Emissions from Saltmarsh Soils to Address Key Blue Carbon Challenges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8033, https://doi.org/10.5194/egusphere-egu23-8033, 2023.

12:20–12:30
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EGU23-12735
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On-site presentation
Giulia Zazzeri, Lukas Wacker, Negar Haghipour, Philip Gautschi, and Heather Graven

Measurements of radiocarbon (14C) in atmospheric methane (CH4) provide a powerful tool to distinguish fossil from biogenic methane emissions, because fossil methane is completely devoid of 14C. However, these measurements are particularly challenging as CH4 is at low concentration in the atmosphere and large volumes of air must be sampled.

At the Laboratory of Ion Beam Physics (LIP), ETH, we developed a portable sampler based on the laboratory prototype in Zazzeri et al. 2021 [1]. The new system enables extraction of carbon from CH4 while sampling in the field, reducing the sample processing in the laboratory and allowing collection of a hundred liters of air onto a 0.5 g zeolite trap.

Here we present an overview of the sampling system and the technical developments that have been implemented at LIP. The relatively small size of the sampler and its interface with the gas ion source of the AMS system make 14CH4 measurements much easier to perform. Its portability will enable collection of CH4 samples in any environment, with the potential of assessing the radiocarbon signature of methane emissions that have not been yet characterized.

[1] Zazzeri, G., Xu, X., & Graven, H. (2021). Environmental Science & Technology, 55(13), 8535-8541.

How to cite: Zazzeri, G., Wacker, L., Haghipour, N., Gautschi, P., and Graven, H.: 14C analysis of atmospheric methane: development of a portable sampling system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12735, https://doi.org/10.5194/egusphere-egu23-12735, 2023.

Posters on site: Tue, 25 Apr, 16:15–18:00 | Hall X5

Chairpersons: Irka Hajdas, Andreas Lang, Arne Ramisch
Radiocarbon as tool to understand the global carbon cycle
X5.236
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EGU23-6028
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Timo Rhyner, Lisa Bröder, Margot White, Benedict Mittelbach, Florian Storck, Lucas Passera, Negar Haghipour, and Timothy Eglinton

Lateral carbon mobilization processes are particularly prone to anthropogenic perturbations due to human intervention of the land surface as well as aquatic corridors yet remain poorly constrained despite their importance as a key component of the C-cycle. A major source of this uncertainty involves processes modulating the sources and fate of carbon along the freshwater aquatic continuum. This study examines the radiocarbon (14C) signatures of particulate and dissolved organic carbon (POC, DOC, respectively) and dissolved inorganic carbon (DIC) transported by Swiss rivers with a view to assessing controls on the origin and cycling of carbon within corresponding watersheds. Twenty-one rivers were selected that span a range of watershed properties and are monitored by the National Long-Term Surveillance of Swiss Rivers (NADUF) program, enabling radiocarbon data to be interpreted within a broader hydrological and geochemical context.  Samples were collected during high-flow conditions in summer 2021, a year of extreme rain events. Average discharge of our sample set (n=21) was 299.76 +/- 513.87 m3/s, while the annual average discharge of all stations was 184.90 ± 264.92 m3/s. The range of D14C values of POC was -158‰ to - 446‰ (n = 21), while corresponding ranges of  D14C values for DOC and DIC were - 43‰ to - 377‰ and - 40‰ to - 301‰, respectively, indicating the presence of pre-aged carbon in all three pools. Hydrological properties such as discharge, runoff and precipitation did not appear as major significant controlling factors. Except for DI14C where annual average runoff of the past decade showed a significant negative correlation. Instead, based on Multivariate Regression Analysis, “alpine” variables such as mean basin elevation, slope, and barren areas were negatively correlated with D14C values of all three D14C-phases, while rivers draining lower elevation terrain, where agricultural land-use is more extensive were associated with higher D14C values in -the organic carbon pools (POC, DOC). Repeated sampling under different hydrological conditions and associated 14C (and 13C) measurements are being used to provide additional insights into the controls on the amount and nature of carbon exported by Swiss rivers, the interconnectivity between different carbon pools within the corresponding drainage basins and ecoregions, as well as to predict long-term trends in the context of changing climate and anthropogenic forcing.

How to cite: Rhyner, T., Bröder, L., White, M., Mittelbach, B., Storck, F., Passera, L., Haghipour, N., and Eglinton, T.: Radiocarbon signatures of carbon phases exported by swiss rivers in the Anthropocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6028, https://doi.org/10.5194/egusphere-egu23-6028, 2023.

X5.237
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EGU23-8148
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ECS
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Benedict V.A. Mittelbach, Margot E. White, Timo Rhyner, Stephan Wartenweiler, Negar Haghipour, Martin Wessels, Thomas M. Blattmann, Nathalie Dubois, and Timothy I. Eglinton

The residence time of carbon in terrestrial ecosystems, such as soils and freshwater, sets the pace of the terrestrial carbon cycle. Understanding export pathways and turnover times of soil organic carbon (OCSoil) is crucial to assess responses to climate and land use changes. Our study aims to quantify the average turnover time of OCSoil in the catchment of perialpine Lake Constance. Lake sedimentary sequences integrate organic carbon from their catchment and aquatic primary productivity. They act as both burial sites of organic carbon (OC) and time series archives of catchment processes. Thus, they can bridge the gap between plot scale observations, e.g., on soil carbon turnover, and observations made at the outlet of major river systems.

Sedimentary organic carbon sources include aquatic primary productivity, OCSoil, and rock-derived (petrogenic) OC. Stable carbon isotopes (δ13C) can be used to identify the relative contribution of these pools. The 5700-year half-life of radiocarbon (14C) coupled with the atmospheric nuclear bomb spike in the early 1960s can be used to infer the age and turnover rate of the OC pools on millennial to annual timescales. Bulk OC isotope analysis of a varved sediment core spanning the past ca. 110 years at quasi-annual resolution was used to constrain the age of soil carbon delivered to Lake Constance. We combined the geochemical data with a Markov-Chain-Monte-Carlo-based approach to identify the most probable age structure of aquatic and soil-derived OC components and to quantify their respective contributions in addition to petrogenic OC.

Radiocarbon analysis of sedimentary bulk OC reveals a well-defined but muted bomb spike in the early 1960s. However, bulk Δ14COC values remain below 0‰, implying a predominance of aged OC. Based on the δ13C-based three-component linear mixing model, we found these values to be the result of an OC mixture containing approx. 40% pre-aged soil carbon and up to 20% fossil petrogenic carbon.  Accounting for these inputs, we estimated that soil-derived OC delivered to Lake Constance is centennial in age, implying interim storage prior or subsequent to erosion from the landscape.

How to cite: Mittelbach, B. V. A., White, M. E., Rhyner, T., Wartenweiler, S., Haghipour, N., Wessels, M., Blattmann, T. M., Dubois, N., and Eglinton, T. I.: Using the radiocarbon bomb spike to constrain the age of soil organic carbon delivered to Lake Constance sediments., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8148, https://doi.org/10.5194/egusphere-egu23-8148, 2023.

X5.238
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EGU23-14183
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ECS
Alexander Brunmayr, Heather Graven, Timo Rhyner, Margaux Moreno Duborgel, and Negar Haghipour

Lateral carbon transport through inland waters plays a critical yet often overlooked role in the delicate balance of carbon exchanges controlling the net uptake and storage of anthropogenic carbon in terrestrial ecosystems. Though new terrestrial carbon cycle models are increasingly making an effort to explicitly represent these traditionally neglected lateral fluxes, the parameters governing lateral carbon transport, particularly the composition and ages of exported soil carbon, remain ill-constrained. In this study, we explore the power of combined river and soil 14C datasets as a parameter constraint when calibrating a novel carbon cycle model connecting the terrestrial and riverine systems in catchments of Switzerland. For the riverine data, we use 14C measurements of particulate organic carbon (POC), dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) for water samples collected during high-discharge events in 2021 across Switzerland. Within those river catchments, we have forest soil 14C data at various depths down to 60cm for up to three samples in time (mid 1990s, 2014, and 2022). The soil samples were split into the following representative fractions: soil dissolved organic carbon (soil-DOC), particulate organic carbon (soil-POC), and mineral-associated organic carbon (soil-MOC), which represents the older and more recalcitrant component of soil carbon. This study investigates to what extent using these fraction-specific 14C measurements together with 13C and nitrogen data for both rivers and soils allows us to not only distinguish the different sources of riverine carbon but further analyze the composition and age of the soil organic carbon ending up in Swiss rivers.

How to cite: Brunmayr, A., Graven, H., Rhyner, T., Moreno Duborgel, M., and Haghipour, N.: Radiocarbon constraints on lateral export of soil organic carbon in rivers of Switzerland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14183, https://doi.org/10.5194/egusphere-egu23-14183, 2023.

X5.239
|
EGU23-10967
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ECS
Katherine Grant, Marisa Repasch, Kari Finstad, Taylor Broek, Jennifer Pett-Ridge, and Karis McFarlane

Soils mediate the rapid cycling of carbon through the critical zone. Soil organic carbon (SOC) is composed of a complex mixture of plant and microbial derived organic compounds with distinct cycling timescales. The residence time of individual SOC components depends on a combination of factors, including compound reactivity, mineral association, and climate conditions, making it difficult to accurately quantify. However, radiocarbon analysis of specific compound classes can disentangle the mixture of SOC ages within a single sample. We modified methods to measure the Δ14C of distinct compound classes (lipids, amino acids, and carbohydrates) from bulk and physically fractionated grassland soils. Additionally, we measured the Δ14C of the water-extractable fraction (WEOC) and the residual acid-insoluble fraction. Samples were collected from a series of grassland meadows across California ranging in climatic conditions including temperature and precipitation. Sites include grassland meadows in Angelo Coast Range Reserve, Hopland Extension Reserve and Sedgwick reserve, and which receives 2160, 940, and 380 mm yr-1 of rainfall and is dominated by Avena spp. We sampled 1m soil pits by ~10cm intervals to study changes in SOC persistence with depth. We used solid state 13C-NMR to measure the relative abundance of the target compound classes in soil. The Δ14C of bulk soil decreased from about +50‰ to about +10‰ in the O-horizons to a range of about -150‰ to about -650‰ in the deepest horizons. At the Hopland site, the clay fraction (<63μm) had higher Δ14C values than both the bulk (<2mm) and sand (<2mm to >63μm) fractions. WEOC Δ14C values ranged from modern to about -45.6‰. Δ14C values of total extracted lipids ranged from 36±4‰ at the surface to -215±3‰ at depth. Quantifying the age distribution of distinct compound classes gives a direct measurement of the persistence between these phases.

How to cite: Grant, K., Repasch, M., Finstad, K., Broek, T., Pett-Ridge, J., and McFarlane, K.: Initial radiocarbon (14C) results of compound class persistence across a climate gradient in California grassland soils, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10967, https://doi.org/10.5194/egusphere-egu23-10967, 2023.

X5.240
|
EGU23-7006
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ECS
Franziska A. Lechleitner, Christopher Day, Jens Fohlmeister, Sophie Warken, Norbert Frank, Heather Stoll, and Caroline Welte

Speleothems, secondary cave carbonate precipitates, can serve as tools to reconstruct past terrestrial ecosystem processes, particularly related to soil and vegetation. Radiocarbon, often in conjunction with other geochemical proxies, has been increasingly used for this purpose, as the speleothem reservoir effect retains useful information on local ecosystem conditions. On the other hand, speleothems are also of interest to the radiocarbon community as they can be dated very precisely with the U-Th method, which may allow the reconstruction of atmospheric radiocarbon levels in time if the reservoir effect remained constant.

Over the past decades, a growing number of speleothem radiocarbon records have been generated from vastly different climate zones and ecosystem types. While much progress has been made in the interpretation of these records, a unified and global view of the factors driving variability in speleothem radiocarbon is still lacking. We compiled a global dataset of averaged speleothem radiocarbon measurements, and provide a critical evaluation of the applicability of the radiocarbon reservoir effect as a proxy for past ecosystem conditions. We compare our dataset to geographic (latitude, elevation), climatic (temperature and precipitation), and ecosystem and geological parameters (soil and bedrock thickness, soil age, vegetation type, and land cover). Our preliminary results show that it is difficult to extract a strong globally relevant driving factor for the mean absolute value in the reservoir effect at the investigated cave sites, and highlights the importance of detailed reporting of local conditions.

To provide insight into the amplitude range of processes affecting published speleothem radiocarbon records we perform a series of numerical forward modeling experiments. We test how the effects of changing soil age, soil pCO2, carbonate dissolution regime, and pyrite oxidation affect carbon isotopes in stalagmites.

Together, the global synthesis and modeling experiments provide us with the first global overview of how cave site parameters and climate and ecosystem processes affect speleothem radiocarbon records, and allow us to assess the sensitivity of this proxy as a tool for past ecosystem conditions.

How to cite: Lechleitner, F. A., Day, C., Fohlmeister, J., Warken, S., Frank, N., Stoll, H., and Welte, C.: A global synthesis of speleothem radiocarbon data – is it a sensitive proxy for past ecosystem processes?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7006, https://doi.org/10.5194/egusphere-egu23-7006, 2023.

X5.241
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EGU23-7936
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ECS
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Sarah Rowan, Marc Luetscher, Sönke Szidat, Thomas Laemmel, Oliver Kost, and Franziska Lechleitner

The cycling of subsurface karst CO2 is not well constrained in terms of its source and transportation pathway. The classical model suggests that cave CO2 is produced by the respiration of soils and vegetation in the catchment. In contrast, several new studies have proposed that the dominant source of CO2 is from the respiration of older organic matter situated deeper within the karst, or from the degassing of supersaturated drip water.

We present over a year of monitoring data from Milandre cave, northern Switzerland, whereby we evaluated the 14CO2 and δ13CO2 composition of the atmosphere in the cave catchment, catchment soil gas, well gas, and cave air. Drip waters located throughout the cave also underwent various analysis. The cave 14CO2 is more depleted compared to the soil and gas samples. The Keeling plot intercept of atmospheric and cave δ13CO2 is ~-26‰, indicating a dominant contribution from biological respiration. The dissolved inorganic carbon from various cave drips have an F14C from ~ 0.84 to 0.96 and δ13C from ~ -16‰ to -11‰. F14C and δ13C are inversely correlated.  Considering both the 14C and δ 13C results, this suggests either a source of CO2 from an aged reservoir of respiring organic matter contributing to the cave gas or substantial influence from degassing of 14C fossil carbonate CO2 from drip water. These results have implications for the understanding of the subterranean carbon cycle and the interpretation of speleothem carbon isotope records for paleoclimate studies.

How to cite: Rowan, S., Luetscher, M., Szidat, S., Laemmel, T., Kost, O., and Lechleitner, F.: Sources of cave CO2 at Milandre cave, Switzerland constrained through multipool analysis of 14C and δ13C., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7936, https://doi.org/10.5194/egusphere-egu23-7936, 2023.

Geochronological applications to characterize Quaternary paleoenvironments
X5.242
|
EGU23-1003
Ludwig Zoeller

Last glacial loess in Poland was deposited under periglacial conditions nearby to the regional maximum advance of the Scandinavian Ice Sheet during the Weichselian glaciation. Its glacier advance and retreat stages are expected to be mirrored in Loess-Paleosol Sequences (LPS) calling for reliable and exact dating. In the Bayreuth luminescence laboratory (BT) established modern SAR protocols of optical dating (OSL, pIRSL) were applied to the 4-11µm fine grain fraction of 38 loess samples from four LPS, distributed from Silesia to the Volhynian upland. Results were compared to published results from the Gliwice luminescence laboratory. Pleasing basic agreement even for surprising results is overshadowed however by somewhat differing apparent ages complicating a sound palaeoclimatic interpretation. A comparison of OSL and pIRIR ages obtained in BT poses a similar problem. OSL ages from quartz are prone to dose-dependent age underestimates but the critical absorbed dose may be grainsize-dependent. Experiences in BT resulted in favoring the fine grains from quartz, allowing for higher credible ages. Nevertheless, our quartz ages > ca. 50 ka are possibly but not necessarily underestimated, obviously dependent on the site and the providence of the quartz grains. In contrast, pIRIR ages turn out to be prone to overestimates due to incomplete bleaching leaving an unknown residual dose at deposition, a serious problem for beds with strong periglacial reworking.

Loess stratigraphy in Poland is well-based mainly on lithostratigraphy, palaeopedology, and periglacial geomorphology. Apart from – often problematic – radiocarbon dating and contradictory previous TL and OSL ages there is a lack however of independent physical dating methods and also of tephrostratigraphic markers. But at least the age of a prominent interstadial soil (or soil complex) now labelled L1SS1 at the end of the Middle Pleniglacial can now be fixed between ca. 30 and ca. 40 ka. Interpretation of dating results from samples older than L1SS1 is challenging. The observed diverging ages (OSL, pIRIR) are critical for the accurate time bracketing of geomorphologic and pedostratigraphic features such as ice wedging, thermokarst erosion events and interstadial soil formations and for their attribution to marine isotope stages. Alternative interpretations are discussed including possible periglacial mirroring of pre-LGM regional ice advances (Ristinge and Klintholm advances) in the southwestern Baltic Sea area.

I suggest that the strange behavior of quartz ages from different grain sizes is caused by various sources (ranging from Paleozoic crystalline rocks to Quaternary glacial drift) with very different geological and thermal histories, stored due to the very high resistance of quartz against weathering. Local and remote sources contribute to individual sedimentary beds of LPSs to varying extents. Thus, fine grains and coarser grains from an individual sample may be derived from diverse sources. In spite of the addressed uncertainties, for honesty reasons it is so far recommended aiming at age bracketing as narrowly as possible, simultaneously using OSL from different quartz fractions and pIRIR from fine polymineral grains. A refinement of this approach remains challenging as far as the sole reliable dating protocol is not ensured.

How to cite: Zoeller, L.: Ambiguity of luminescence ages from periglacial loess in Poland – “As you like it” or honesty with users?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1003, https://doi.org/10.5194/egusphere-egu23-1003, 2023.

X5.243
|
EGU23-6579
Daniela Constantin, Robert Begy, Dimitri Vandenberghe, Daniel Veres, and Alida Timar-Gabor

An increasing number of studies exploit the advantages of a single-aliquot regenerative-dose protocol (SAR) for equivalent dose determination with sampling at relatively closely-spaced vertical intervals (of the order of 10-30 cm). The resulting ages are, at least in principal, ideally suited for age-depth modelling. The modelling, however, is made difficult owing to the variety and complex combination of uncertainties associated with luminescence dating. Moreover, we previously reported on a variability in age results for coeval loess samples that is significantly larger than expected and remains to be understood.

In this study, we examine this problem explicitly by observing the degree of precision and accuracy that can be achieved by luminescence dating of multiple coeval loess samples of known age. The main goal is to improve our understanding of how luminescence ages are to be incorporated into age-depth models, thus increasing their robustness and accuracy.

Fourteen samples were taken at closely-spaced horizontal intervals from loess deposits immediately over- and underlying the Campanian Ignimbrite/Y5 tephra layer (40Ar/39Ar dated to 39.2±0.1 ka), as exposed at a section in the Lower Danube Basin in southeastern Europe. Luminescence analyses were carried out using the single-aliquot regenerative-dose (SAR) protocol and OSL signals from 63-90 µm quartz fraction. We report an average age of 46 ka for the samples collected below the tephra layer and 40 ka for the samples collected above it. The individual random and systematic uncertainties contributing to the individual ages vary from 1.9 % to 5.4 % and from 6.0 % to 6.1 %, respectively. We obtain an improved overall precision on the age of the sedimentary context by calculating the weighted average age and combining the individual random and systematic uncertainties following Aitken (1985, Appendix B). Thus we report weighted average ages of 46 ka and 40 ka for the horizontally sampled sediment layers intercalating the ash layer and associated overall random uncertainties of 1.3 % and 1.1 %. The overall systematic uncertainties are 6.1 % and 6.0 %. The insights gained from this are discussed in relation to age-modelling studies of luminescence-dated paleoclimate archives, and loess deposits in particular.

Keywords: luminescence dating; precision; random uncertainty; quartz

How to cite: Constantin, D., Begy, R., Vandenberghe, D., Veres, D., and Timar-Gabor, A.: An empirical study on the variability of luminescence ages for coeval loess samples, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6579, https://doi.org/10.5194/egusphere-egu23-6579, 2023.

Technical advancements in Quaternary geochronology
X5.244
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EGU23-1396
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ECS
|
Simon Larsson and Matthew Bolton

Tephrochronology is often used for dating of natural archives and for correlation between study sites. Volcanic ashes (tephra) extracted from cores used for climate reconstructions function as common time-marker horizons and become anchor points in comparisons of age models from different studies. Given these uses, tephrochronology is well placed to help overcome the chronological challenges that hinder sufficiently precise dating of palaeoclimate records.

Tephras are identified based on their geographic and stratigraphic contexts, glass shard morphology, and geochemical composition. The geochemistry is most commonly analysed by electron probe microanalyser and presented as weight percentages of oxides of the nine or ten most abundant elements, often normalised to a 100 % total for ease of comparison. A simple exploration of such results and comparison to published data of previous tephra findings is usually enough for confident identification. However, compositional data of tephra findings from new studies continuously add to the complexity of tephrochronological investigations by increasing the amount of data available for comparison, including the addition of new potential candidates for identification. The increased likelihood of multiple candidates—sometimes with overlapping geochemistries—means that statistical data analyses are increasingly necessary.

Tephrochronologists have used principal component analysis and discriminant function analysis in situations needing statistical approaches, but these methods’ validity often requires certain assumptions not to be violated. A rarely considered example of such an issue is that compositional data suffers from the constant-sum constraint and must be converted by log-ratio transformations for some statistical analyses to function properly. As there is presently no consensus on a tephra compositional data curation procedure including log-ratio transformations, we have explored several variations and compared the results to see if a formal recommendation for such a procedure is relevant for the tephra community.

How to cite: Larsson, S. and Bolton, M.: Tephra compositional data: are we doing it right?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1396, https://doi.org/10.5194/egusphere-egu23-1396, 2023.

X5.245
|
EGU23-2934
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ECS
Kari Finstad, Erin Nuccio, Katherine Grant, Jennifer Pett-Ridge, and Karis McFarlane

Soils are a significant component of the Earth’s carbon (C) cycle, yet a mechanistic understanding of what controls the turnover of this large C pool remains elusive. Microbial respiration of organic C accounts for roughly half of the total CO2 production from soils, though limited options exist for accurately identifying the source of C assimilated by microbial communities. Currently, radiocarbon (14C) analysis of evolved CO2 from soil incubations is the most common laboratory method for this, however they can introduce artifacts due to sample disruption and processing and can take months to produce sufficient CO2 for analysis. We present novel extraction methods which allow for the direct 14C analysis of microbial biomolecules and compare the results to laboratory incubations. Preliminary results suggest that in the upper 50 cm soil depths, the Δ14C from incubations is indistinguishable from that of extracted microbial biomass. Below 50 cm, the Δ14C of the microbial biomass is more depleted than that of the incubations, either due to the stimulation of labile C decomposition in the incubations, or the inclusion of biomolecules from non-living cells in the biomass extractions. Work is ongoing to identify the source of the extracted biomass pool and additional methods for isolating specific, short-lived biomolecules such as RNA, are underway to unambiguously determine the Δ14C of organic molecules being assimilated by active microbial communities.

How to cite: Finstad, K., Nuccio, E., Grant, K., Pett-Ridge, J., and McFarlane, K.: Novel methods for determining the 14C age of microbially assimilated soil carbon, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2934, https://doi.org/10.5194/egusphere-egu23-2934, 2023.

X5.246
|
EGU23-11860
Negar Haghipour, Maarten Lupker, Lukas Wacker, Margot White, Lisa Bröder, and Timothy I. Eglinton

Radiocarbon measurements of dissolved organic carbon (DOC) can give us valuable information about origin and age of DOC, a major, yet little understood component in the global carbon cycle. One way to measure DOC in water is to remove dissolved inorganic carbon first, oxidize organic carbon with UV irradiation and ultimately analyses the formed inorganic CO2 for 14C. The main challenge of UV-Oxidation (UVox) methods is to extract the typically low concentrations of DOC with low blanks required for relatively high precision 14C measurements. A disadvantage of currently used UVox methods is that only one sample can be oxidized in a laborious process at the same time in large volume. Here we present a UV-Oxidation system where up to 12 water samples can be oxidized simultaneously in 12 separate quartz reactors arranged around a single UV lamp in a compact setup. The simple setup further uses helium instead of vacuum typically used by conventional extraction lines to speed up the extraction of the formed CO2 after oxidation. The key improvements of the new UVox setup are: 1) Reduced amount of water needed (30- 60 ml) as samples are measured for 14C with the Micadas gas ion source., 2) UV oxidation efficiency for standards is high (96%), 3) No KI trap is needed, 4) Required time for sample preparation of up to 12 samples is 4-6 h, 5) combined the CO2 from different reactors to one trap.  We obtained 2.6 ± 0.6 µgC with F14C= 0.27±0.05 for processing blank.  We will present the first measurments of DOC samples from Swiss lakes, Canadian Beaufort Sea and the reproducibility of the line.

How to cite: Haghipour, N., Lupker, M., Wacker, L., White, M., Bröder, L., and Eglinton, T. I.: A new UV-Oxidation set up for AMS radiocarbon analysis for small dissolved organic carbon in marine and fresh water samples, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11860, https://doi.org/10.5194/egusphere-egu23-11860, 2023.

X5.247
|
EGU23-8974
Soenke Szidat, Thomas Laemmel, Dylan Geissbühler, Sarah Rowan, Philip Gautschi, Franziska Lechleitner, and Lukas Wacker

Radiocarbon (14C) measurements of atmospheric greenhouse gases such as carbon dioxide (CO2) and methane (CH4) are central in our capability to identify their provenance. The 14C content of these gases provides more insight into the age of their sources and mainly allows the distinction between fossil and modern ones. 14CO2 measurements can be used to analyze the nature of anthropogenic emissions (mostly fossil), or to discern on what organic matter pool respiration is taking place in a given environment. 14CH4 can also be used to detect anthropogenic emissions (from leaks of natural gas, for example) as well as natural emissions produced by methanogenesis, for example from ruminants or in wetlands.

The 14C analysis of atmospheric gases is made challenging due to their usual low concentration. Thus making the use of appropriate sampling methods, preconcentration and extraction techniques necessary to reach a sufficient amount of carbon for Accelerator Mass Spectrometry (AMS) analysis. We propose here a general view of the techniques that were developed at the Laboratory for Ion Beam Physics (ETHZ, Zurich), and at the Laboratory for the Analysis of Radiocarbon with AMS (UNIBE, Bern) for the purpose of analyzing CO2 and CH4 in atmospheric samples. We then discuss the practicability and the potential bias introduction of each of them.

The techniques are as follows :

  • Automated Graphitization Equipment with Automated Loading Facility (AGE-ALF)
  • Automated Graphitization Equipment with Cryogenic Trap (AGE-CT)
  • Methane Preconcentration and Purification System (MPPS)

Generally, samples were collected in sampling bags, either in 5-15L capacity for CO2 or larger than 60L for CH4. Types of samples that are considered are atmospheric CO2 and CH4 samples, CO2 from soil respiration, and CO2 from cave air. The different techniques are presented, and 14C results from standard gases are compared between the extraction lines and two MICADAS AMS systems at ETHZ and UNIBE.

How to cite: Szidat, S., Laemmel, T., Geissbühler, D., Rowan, S., Gautschi, P., Lechleitner, F., and Wacker, L.: New developments in techniques for the sampling and analysis of atmospheric 14CO2 and 14CH4 at ETHZ and UNIBE, Switzerland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8974, https://doi.org/10.5194/egusphere-egu23-8974, 2023.

X5.248
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EGU23-1551
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ECS
|
Melina Wertnik, Lukas Wacker, Nicolas Brehm, and Caroline Welte

The unique laser ablation (LA) setup at ETH Zurich (Switzerland), coupled to a MICADAS accelerator mass spectrometer (AMS), enables rapid 14C analyses and has been successfully employed for a broad range of carbonate archives such as stalagmites (Welte et al., 2021), otoliths (Andrews et al., 2019), and shells of Arctica islandica. An 193 nm ArF excimer laser is used to liberate CO and CO2 from the sample surface by ablation. The gas is then flushed with helium into the gas ion source of the AMS for online measurement.

Advantages of the novel techniques are a significant reduction in labour-intensive sample preparation and the speed of measurement, which minimises the expensive beam-time of the AMS. However, as a transient signal is measured where each sampling location is only measured for a short duration, uncertainties associated with LA-AMS are significantly higher than for conventional measurement techniques. Still, it is possible to locate strong signals such as a growth stop or the bomb spike very rapidly and precisely using only two scans of the sample. Here we present the status of the setup and progress on data reduction aimed at reducing the larger uncertainties. Preliminary results from comparisons of parallel tracks on a stalagmite allow testing the data reduction strategy and will be shown.

Andrews, A. et al. (2019), Marine and Freshwater Research, https://doi.org/10.1071/mf18265

Welte, C. et al. (2021), Climate of the Past, 17(5), 2165–2177, https://doi.org/10.5194/cp-17-2165-2021

How to cite: Wertnik, M., Wacker, L., Brehm, N., and Welte, C.: Continuous Radiocarbon Records by Laser Ablation – Status Report, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1551, https://doi.org/10.5194/egusphere-egu23-1551, 2023.

Posters virtual: Tue, 25 Apr, 16:15–18:00 | vHall CL

Chairpersons: Negar Haghipour, Arne Ramisch
Geochronological applications to characterize Quaternary paleoenvironments
vCL.15
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EGU23-12675
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ECS
A new empirical reconstruction of paleoglacier flow lines for the last glacial cycle, spanning high-mountain Asia
(withdrawn)
Robin Blomdin, Irina Rogozhina, Jakob Heyman, Andrés Castillo-Llarena, Jogscha Abderhalden, and Lukas Hillisch