BG2.2 | Stable isotopes and novel tracers in atmospheric and biogeosciences
EDI
Stable isotopes and novel tracers in atmospheric and biogeosciences
Co-organized by AS3
Convener: Getachew Adnew | Co-conveners: Jan Kaiser, Eliza Harris, Nerea Ubierna
Orals
| Thu, 18 Apr, 08:30–10:10 (CEST)
 
Room 2.95
Posters on site
| Attendance Thu, 18 Apr, 16:15–18:00 (CEST) | Display Thu, 18 Apr, 14:00–18:00
 
Hall X1
Orals |
Thu, 08:30
Thu, 16:15
We welcome contributions involving the use of stable isotopes of light elements (C, H, O, N, S) or novel tracers (such as COS) in field and laboratory experiments, the latest instrument developments, as well as theoretical and modelling activities, which advance our understanding of biogeochemical and atmospheric processes. We are particularly interested in the latest findings and insights from research involving:

- Isotopologues of carbon dioxide (CO2), water (H2O), methane (CH4), carbon monoxide (CO), oxygen (O2), carbonyl sulfide (COS), and nitrous oxide (N2O)
- Novel tracers and biological analogues
- Polyisotopocules including "clumped isotopes"
- Non-mass-dependent isotopic fractionation and related isotope anomalies
- Intramolecular stable isotope distributions ("isotopomer abundances")
- Quantification of isotope effects
- Analytical, methodological, and modelling developments
- Flux measurements

Orals: Thu, 18 Apr | Room 2.95

Chairperson: Nerea Ubierna
08:30–08:40
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EGU24-2219
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On-site presentation
Dan Yakir, Jonathan Muller, Rafael Stern, Rafat Qubaja, and Yasmin Bohak

Carbon monoxide (CO) is produced in living plants and can act as a stress-signaling molecule in both animals and plants. While CO emissions from soil, litter decomposition, and incomplete combustion have been extensively studied, there is a scarcity of research on CO flux from living vegetation, particularly under field conditions. We present the results of continuous CO fluxes measurements (together with those of water, CO2, and COS) using twig chambers in summer-droughted and in non-droughted (irrigated) Pinus halepensis trees across the seasonal cycle. We found significant CO emissions from leaves, which were correlated with environmental parameters (radiation, leaf temperature, and VPD). It peaked under the stressful summer conditions at the study site, when CO2 exchange and leaf conductance were at a minimum.  The CO fluxes were strongly correlated to twig transpiration and were enhanced under irrigated treatment. It is speculated that leaf CO emission is related to biotic reactions, such as heme degradation, which is enhanced under stress conditions and is possibly associated with photorespiration. Our results provide a rare, high-resolution, annual scale study of the environmental factors controlling leaf CO emissions under field conditions and indicate that including it in plant gas exchange studies may provide additional means to interpret their response to stress.

How to cite: Yakir, D., Muller, J., Stern, R., Qubaja, R., and Bohak, Y.: Leaf carbon monoxide emission under field conditions: a potential stress indicator?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2219, https://doi.org/10.5194/egusphere-egu24-2219, 2024.

08:40–08:50
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EGU24-1257
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ECS
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On-site presentation
Anna de Vries, Georg Wohlfahrt, Timo Vesala, and Kukka-Maaria Kohonen

Previous studies inferred a missing sink of carbonyl sulfide (COS) in high Northern latitudes. Boreal COS budgets, however, typically account solely for the contribution by forests and ignore any uptake that widespread wetland ecosystems may contribute. Here we present the first direct measurements of the ecosystem-atmosphere COS exchange of a boreal wetland and compare this with a needleleaf forest ecosystems. We then use these data to up-scale to the boreal region.

We found that the investigated wetland was a stable sink for COS during the vegetation period, taking up on average of 10 pmol m−2s−1COS. While this was just 64% of the forest COS uptake, upscaling to the boreal region using the ORCHIDEE land surface model revealed that the Northern wetland sink, c. 20 GgS/y, was on the same order of magnitude compared to the forest COS sink. Our results thus indicate that northern COS should not neglect contributions by wetland ecosystems.

How to cite: de Vries, A., Wohlfahrt, G., Vesala, T., and Kohonen, K.-M.: On the contribution of boreal wetlands to the Northern Hemisphere carbonyl sulfide sink, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1257, https://doi.org/10.5194/egusphere-egu24-1257, 2024.

08:50–09:00
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EGU24-15555
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ECS
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On-site presentation
Gerbrand Koren, Kim A. P. Faassen, Raquel González-Armas, Getachew Agmuas Adnew, Hella van Asperen, Hugo de Boer, Santiago Botía, Oscar Hartogensis, Lucas Hulsman, Ronald W. A. Hutjes, Sam P. Jones, Shujiro Komiya, Ingrid T. Luijkx, Wouter Mol, Michiel van der Molen, Robbert Moonen, Thomas Röckmann, and Jordi Vilà-Guerau de Arellano

Diurnal temperature and carbon dioxide ranges are key metrics to quantify the impact of regional climate changes in forests. These ranges depend on biophysical processes, surface heat, water and carbon exchange, and boundary-layer dynamics. A crucial and elusive process is the entrainment of air from the free troposphere and residual air layers into the atmospheric boundary layer. Here we provide observational constraints on entrainment for two contrasting measurement sites: the Amazon Tall Tower Observatory (ATTO) in central Amazonia and the Loobos flux tower (NL-Loo) in a temperate forest in the Netherlands. We used radio soundings, air samples from tall towers and aircraft data in combination with surface air measurements and ecophysiological data. Fluxes and concentrations were measured for biophysical-process tracers  CO2, O2/N2, δ13C, δ18O (in CO2) and δ18O (in water). These novel tracers are proposed to partition gross carbon and water fluxes and for estimating plant properties and we present a unique dataset with our interpretation. Our analysis enables us to unravel the role of entrainment on the diurnal ranges and how this is controlled by surface and entrainment fluxes. By means of a coupled forest-atmosphere model constrained by the comprehensive observations, we perform a sensitivity study on the surface flux partitioning (photosynthesis versus soil respiration; soil evaporation versus plant transpiration, sensible versus heat flux) under a wide range of leaf traits, surface and boundary-layer dynamic conditions. Our results are useful to assess the performance of carbon-climate models in tropical and temperate forests.

How to cite: Koren, G., Faassen, K. A. P., González-Armas, R., Adnew, G. A., van Asperen, H., de Boer, H., Botía, S., Hartogensis, O., Hulsman, L., Hutjes, R. W. A., Jones, S. P., Komiya, S., Luijkx, I. T., Mol, W., van der Molen, M., Moonen, R., Röckmann, T., and Vilà-Guerau de Arellano, J.: Tracing diurnal variations of carbon and water cycle tracers over a tropical and temperate forest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15555, https://doi.org/10.5194/egusphere-egu24-15555, 2024.

09:00–09:10
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EGU24-6354
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ECS
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On-site presentation
Pharahilda Steur, Hubertus A. Scheeren, Gerbrand Koren, Getachew A. Adnew, Wouter Peters, and Harro A. J. Meijer

We present multiple year records of the triple oxygen isotope signature Δ(17O) of atmospheric CO2 conducted with laser absorption spectroscopy, from Lutjewad in the Netherlands (53° 24’N, 6° 21’E) and Mace Head in Ireland (53° 20’ N, 9° 54’ W). Measurements were done on flask samples covering the period 2017-2022. The average uncertainty of 0.07 is about 3 times smaller than the total observed variability. A positive Δ(17O) originates from intrusions of stratospheric CO2, whereas values close to zero result from equilibration of CO2 and water, predominantly happening inside plants due to enhanced dissolution in the presence of carbonic anhydrase. A biosphere driven seasonal signal is, however, not observed in the records. Both records show significant interannual variability, of up to 0.3 . The total range covered by smoothed monthly averages from the Lutjewad record is -0.065 to 0.046 , which is significantly higher than the range of -0.009 to 0.036 that was simulated with a 3-D transport model. One of the major model uncertainties is the representation of the stratospheric influx of Δ(17O). We modified the model using the 100 hPa 60-90° North monthly mean temperature anomaly as a proxy to scale stratospheric downwelling. This results in a strong improvement of the correlation coefficient of the simulated and the observed year-to-year Δ(17O) variations at Lutjewad over 2019 and 2022 from 0.37 to 0.81 (N=22). To infer terrestrial carbon fluxes, the contribution of the stratosphere to the observed signal should therefore be considered. In fact, as the Δ(17O) of atmospheric CO2  seems to be dominated by stratospheric influx, it might be used as a tracer for stratosphere-troposphere exchange. To further study the potential of Δ(17O) of atmospheric CO2 as a tracer for stratosphere-troposphere exchange at Lutjewad, we installed a laser absorption spectrometer at the measurement station for in-situ measurements. At Lutjewad numerous other atmospheric species are monitored, such as N2O, Rn and 14C. This will enable us to deepen our knowledge on the mechanisms that drive the interannual variability of Δ(17O) of atmospheric CO2  that we observe at Lutjewad.

 
 

How to cite: Steur, P., Scheeren, H. A., Koren, G., Adnew, G. A., Peters, W., and Meijer, H. A. J.: Interannual variations in Δ(17O) of atmospheric CO2 suggest a strong link with stratospheric input, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6354, https://doi.org/10.5194/egusphere-egu24-6354, 2024.

09:10–09:20
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EGU24-13954
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ECS
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On-site presentation
JeongEun Kim, Jinho Ahn, and Sakae Toyoda

 Nitrous oxide (N2O), known for its ozone-depleting potential and characterized by a long residence time of 120 years in the atmosphere, is the third most significant anthropogenic greenhouse gas after CO2 and CH4. Primary sources of N2O include nitrification and denitrification processes in soils and aquatic systems, as well as from direct anthropogenic sources such as fossil fuel combustion and wastewater treatment plants. The increase in N2O emissions due to agricultural activities and urbanization is complex, given the high variability of these emissions. To characterize anthropogenic N2O sources, we collected air samples from tunnels and wastewater treatment plants. Additionally, to establish the background levels for Seoul, a megacity in South Korea, we collected ambient air from three sites (Mt Gwanak, Mt Nam, and Olympic Park) monthly throughout the year 2023. These air samples were measured for greenhouse gas concentrations (CO2, CH4, and N2O), and the stable isotopic compositions of N2O (δ15Nbulk, δ18O, and SP values) were analyzed using IRMS. The stable isotopic ratios of N2O emitted from the vehicles were determined as 6.0 ± 1.2 ‰ for δ15Nbulk, 34.4 ± 11.7 ‰ for δ18O, and 6.0 ± 4.2 ‰ for SP values. Furthermore, N2O from wastewater treatment plant water tank air exhibited variations dependent on dissolved oxygen levels. Notably, the stable isotopic compositions of N2O from anthropogenic sources were consistently depleted compared to the ambient air of Seoul (δ15Nbulk: 5.9± 0.2 ‰, δ18O: 43.8 ± 0.1 ‰, SP: 18.6 ± 0.3 ‰ (S.E.)). Intriguingly, while δ15Nbulk and δ18O values of ambient air were depleted relative to the global average, SP values exhibited a wide range and significant variability. This suggests the presence of pronounced spatial and temporal variabilities in N2O emissions, underscoring the need for further research to understand the extent of anthropogenic impacts.

How to cite: Kim, J., Ahn, J., and Toyoda, S.: Nitrous oxide emissions and stable isotopic composition in urban sources and ambient air in Seoul, South Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13954, https://doi.org/10.5194/egusphere-egu24-13954, 2024.

09:20–09:30
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EGU24-11359
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ECS
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On-site presentation
Lison Soussaintjean, Jochen Schmitt, Joël Savarino, Andy Menking, Edward Brook, Barbara Seth, Thomas Röckmann, and Hubertus Fischer

Ice cores represent the only direct paleo-atmospheric archive that allow the reconstruction of greenhouse gas concentrations such as N2O. However, processes in the ice can alter the atmospheric information stored in air bubbles, for example by adding extra N2O by in situ production. This in situ production of N2O is especially severe in mineral dust-rich ice core sections corresponding to glacial periods. Understanding the production process and its link to the mineral dust content is key to systematically detecting altered samples and correcting for the in situ contribution. Isotope analysis is particularly useful for characterizing these processes and thus isolating the paleoclimatic signal from archived data. 

We measured the bulk nitrogen and oxygen isotopic composition of N2O in Antarctic and Greenland ice cores from glacial periods. The isotopic signatures of N2O produced in situ, calculated using a mass balance approach, differ from that of the atmospheric N2O. In addition, enrichment or depletion in 15N and/or 18O relative to atmospheric values varies with drilling site, snow accumulation rate, and properties of the snow-ice transition. Interestingly, isotopic signatures of nitrate (NO3-) exhibit similar dependencies. It is well established that NO3- is drastically altered by post-depositional processes in low accumulation areas. Joint isotopic analysis of N2O and NO3- in samples from the EDC and EDML ice cores revealed a correlation between δ15N values of NO3- and in situ N2O, pointing to NO3- as a potential precursor for in situ production. While being linearly correlated, the nitrogen isotopic signature of NO3- is twice as enriched as in situ produced N2O. This suggests that the two N atoms of N2O originate from two distinct sources and only one is likely derived from nitrate.

We additionally measured the site preference of 15N in N2O in ice core samples (SP = δ15Nα - δ15Nβ, where α is the central and β the terminal N atom in the N2O molecule). Previous work on SP suggests that SP might be indicative of the N2O formation pathway provided both N atoms are derived from the same N precursor. The SP signature in Vostok samples ranges from +57 to +242 ‰, and the δ15Nα values from +92 to +234 ‰, which is comparable to the δ15N values of NO3- at Vostok. Although similar reaction pathways were expected in different ice cores, in situ N2O from Taylor Glacier samples exhibits very different SP values from -17 to -7 ‰, with δ15Nα values from -45 to -32 ‰. Given that the difference in δ15N of NO3- is also up to 200 ‰ between these two locations, our findings suggest that the center-position nitrogen (α) of in situ N2O comes from NO3- and the terminal-position nitrogen (β) from another N-bearing compound. Thus, the SP signature seems to reflect not the N2O formation pathway but the difference in δ15N of the two nitrogen pools involved in the reaction.

Gaining a thorough understanding of the N2O production in ice marks a significant advancement towards interpretation of the N2O record and possibly correction for in situ production.

How to cite: Soussaintjean, L., Schmitt, J., Savarino, J., Menking, A., Brook, E., Seth, B., Röckmann, T., and Fischer, H.: Investigating the dust-induced N2O production in ice cores using bulk and position-specific isotope analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11359, https://doi.org/10.5194/egusphere-egu24-11359, 2024.

09:30–09:40
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EGU24-16376
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ECS
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On-site presentation
Sara Defratyka, Chris Rennick, Freya Wilson, Matthieu Clog, Andrew Houston, and Tim Arnold

Bulk isotopic signatures (δ13C-CH4 and δD-CH4) are widely used for determination of methane source types and relative contributions. For example, these measurements are implemented as additional tracers in top-down studies. However, for some sources, for example certain fossil fuels sources in Europe and waste sector, the bulk isotopic signatures are overlapping, thus some methane sources remain indistinguishable1–4.

The multiply substituted (clumped) isotopes can be used as additional tracers to better distinguish methane sources, and potentially, better understand methane sinks. Measurement of methane clumped isotopes, Δ13CH3D and Δ12CH2D2 is more challenging than measurements of bulk isotopes and requires more advanced instruments 3,5–8. Currently, a NERC project called POLYGRAM aims to develop the sample preparation (automated preconcentration) and measurement infrastructure to measure atmospheric air samples using High Resolution - Isotope Ratio Mass Spectrometer (HR-IRMS), to determine clumped isotopes from air samples collected at the world-recognised global monitoring sites at Cape Point, South Africa and station Zeppelin, Svalbard. Moreover, the project also aims to determine the clumped isotopes ratios of methane sources, like wetlands, agriculture or coal mines, as currently clumped isotopes database is constrained.

Use of custom-built preconcentrator is a key step in the measurement chain, as HR-IRMS requires ultra-pure methane samples to measure clump isotopes. For ambient air studies, our aim is to obtain, at ambient pressure, a 150 ml sample containing at least 1% of methane from hundreds of litres of ambient air, where CH4 mole fraction is less than 2 ppm. To achieve it, we aim to concentrate methane in our sample by up to 62500 times. Additionally, we develop our preconcentrator to prepare samples containing at least 1% of methane from gas samples containing <1% CH4, like air in coal mines, landfill emissions, etc. During the conference, we will be focused on overcoming technical and scientifical challenges and made progress in developing CH4 preconcentrator. We will present the results of validation exercises to ensure repeatability and lack of fractionation effects, both for ambient air and methane source samples.

References:

  • Turner, A. J., Frankenberg, C. & Kort, E. A. Interpreting contemporary trends in atmospheric methane. Proc. Natl. Acad. Sci. 116, 2805–2813 (2019).
  • Saunois, M. et al. The Global Methane Budget 2000–2017. Earth Syst. Sci. Data 12, 1561–1623 (2020).
  • Chung, E. & Arnold, T. Potential of Clumped Isotopes in Constraining the Global Atmospheric Methane Budget. Glob. Biogeochem. Cycles 35, (2021).
  • Menoud, M. et al. New contributions of measurements in Europe to the global inventory of the stable isotopic composition of methane. Earth Syst. Sci. Data 14, 4365–4386 (2022).
  • Douglas, P. M. J. et al. Methane clumped isotopes: Progress and potential for a new isotopic tracer. Org. Geochem. 113, 262–282 (2017).
  • Haghnegahdar, M. A., Schauble, E. A. & Young, E. D. A model for 12CH2D2 and 13CH3D as complementary tracers for the budget of atmospheric CH4. Glob. Biogeochem. Cycles 31, 1387–1407 (2017).
  • Sivan, M. & Röckmann, T. Extraction, purification, and clumped isotope analysis of methane (Δ13CDH3 and Δ12CD2H2) from sources and the atmosphere. (2023).
  • Haghnegahdar, M. A. et al. Tracing sources of atmospheric methane using clumped isotopes. 120, (2023).

How to cite: Defratyka, S., Rennick, C., Wilson, F., Clog, M., Houston, A., and Arnold, T.: Development and verification of preconcentrator to measure clumped isotopologues (Δ13CH3D and Δ12CH2D2) of methane from the atmosphere and sources, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16376, https://doi.org/10.5194/egusphere-egu24-16376, 2024.

09:40–09:50
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EGU24-13219
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ECS
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On-site presentation
Orestis Gazetas, Andrew Houston, Matthieu Clog, Issaku Kohl, and Fin Stuart

The Witwatersrand Basin is a well-known area due to the immense gold mineralisation and mining activities, which have been ongoing since the late 19th century. The Virginia Gas Field, located in the southernmost extent of the basin, has recently gained further attention due to the discovery of gases with remarkable helium content of up to 12% and methane content between 75-99%. While the helium generation is likely straightforward and linked to the U-rich Dominion (2.9-3.0 Ga) and Central Rand (2.7-2.8 Ga) groups (Lippmann-Pipke et al., 2003), the origin of methane seems more complex but ultimately significant, with economic potential and implications for the evolution of life .

Stable isotopic compositions of carbon and hydrogen (δ13C and δD) along with molecular compositions (C1/C2+) are traditionally considered useful for understanding the origin of methane in natural gas reservoirs but can often be ambiguous or misleading. The recent development of HR-IRMS allows us to delve deeper into the distribution of isotopes beyond bulk ratios by introducing two additional tracers, the clumped isotopic compositions Δ13CH3D and Δ12CH2D2. These novel tracers offer two additional dimensions which can potentially provide insights into the formation pathways and formation or re-equilibration temperature of methane.

For this study, we measured bulk and clumped isotopic compositions along with molecular compositions for samples collected from shallow boreholes (300-700m depth) within the Virginia gas field production area. Here, we present evidence that the bulk and clumped isotopic compositions are governed by the microbial cycling of CH4 due to the presence of ancient microbial communities of methanogens and methanotrophs at depths below 1km (Omar et al., 2003). We also consider the possibility of mixing microbial methane with abiotic gas resulting from water-rock interactions occurring in the deep subsurface.

References

1. Lippmann-Pipke, J., Stute, M., Torgersen, T., Moser, D.P., Hall, J., Lin, L., Borcsik, M., Bellamy, R.E.S. and Onstott, T.C., 2003. Dating ultra-deep mine waters with noble gases and 36Cl, Witwatersrand, South Africa. Geochimica Cosmoshimica Acta, 67, pp.4597-4619.

2. Omar, G.I., Onstott, T.C. and Hoek, J., 2003. The origin of deep subsurface microbial communities in the Witwatersrand Basin, South Africa as deduced from apatite fission track analyses. Geofluids, 3(1), pp.69-80.

 

How to cite: Gazetas, O., Houston, A., Clog, M., Kohl, I., and Stuart, F.: Deciphering the origin of methane in fracture fluids at Virginia gas field using clumped isotope tracers., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13219, https://doi.org/10.5194/egusphere-egu24-13219, 2024.

09:50–10:00
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EGU24-20419
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ECS
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On-site presentation
Alessandro Zanchetta, Steven van Heuven, Jin Ma, Maarten Krol, and Huilin Chen

Carbonyl sulfide (COS) is a long-lived sulfur compound present in the atmosphere with an average mole fraction of around 450-500 ppt, and is considered as a potential tracer to partition gross primary production (GPP) and net ecosystem exchange (NEE) in plants’ photosynthesis, possibly by satellite observations. However, its sources and sinks  are not fully understood, and remote sensing observations of COS still require validation and need to be linked with a reference measurement scale, e.g., NOAA’s. In this work, we present vertical profiles of COS mole fractions obtained in Trainou, France (47°58' N, 2°06' E) in June 2019, in Kiruna, Sweden (67°53' N, 21°04' E) in August 2021, and in Sodankylä, Finland (67°22'N, 26°37'E) in August 2023 using AirCore samplers and two versions of the lightweight stratospheric air (LISA) sampler. Additionally, simultaneous measurements of CO2, CO, CH4 and N2O have been made. Measurement methods (i.e., LISA vs AirCore) will be compared. Moreover, the retrieved COS profiles will be compared with COS FTIR remote sensing observations and COS simulations from the TM5-4DVAR modeling system, to get a better understanding of the behavior of these species in the stratosphere, i.e., the sources and the sinks of COS, as well as vertical structures due to atmospheric transport. Furthermore, these stratospheric observations could be used to estimate the stratospheric lifetime of COS. These findings will improve our understanding of the budget and the variabilities of COS in the stratosphere, and advance the use of remote sensing observations of COS from satellite and ground-based spectrometers to study the global cycle of COS.

How to cite: Zanchetta, A., van Heuven, S., Ma, J., Krol, M., and Chen, H.: Stratospheric observations of carbonyl sulfide using AirCore and LISA, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20419, https://doi.org/10.5194/egusphere-egu24-20419, 2024.

10:00–10:10
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EGU24-15916
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ECS
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On-site presentation
Sean Clarke, Henry Holmstrand, Krishnakant Budhavant, Manoj Remani, and Örjan Gustafsson

Sulfate aerosols are short lived climate forcers that cool the climate, but at the cost of human health and the environment. Their short lifetime leads to an unequal global distribution, with massive emissions in South Asia, resulting in some of the highest atmospheric loadings. These emissions originate from natural and anthropogenic sources, with their relative contributions uncertain, due to emissions being short lived and diffuse. However, the stable isotopic composition (δ34S), holds some promise of improved apportionment of sulfate sources. The aim was to leverage this isotopic composition to distinguish sources of sulfate aerosols intercepted at the Maldives Climate Observatory Hanimaadhoo (MCOH). This site is strategically located to intercept a wide footprint of the outflow from South Asia.

The results demonstrated that non-sea salt sulfate was largely of anthropogenic origin, contributing 93±21%, 85±14%, 61±20% in winter, spring, and summer, respectively. This study also found a moderate to strong correlation (r2 = 0.68) between continental anthropogenic (winter and spring) sulfate (δ34S) and fossil fuel black carbon (δ13C, Δ14C). This study provides improved constraints on sulfate sources in South Asia using stable δ34S isotopic analysis, which builds a foundation for future investigations aimed at unravelling the nexus of sulfate emissions in South Asia.

How to cite: Clarke, S., Holmstrand, H., Budhavant, K., Remani, M., and Gustafsson, Ö.: Source apportionment of sulfate aerosols over South Asia using δ34S, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15916, https://doi.org/10.5194/egusphere-egu24-15916, 2024.

Posters on site: Thu, 18 Apr, 16:15–18:00 | Hall X1

Display time: Thu, 18 Apr, 14:00–Thu, 18 Apr, 18:00
Chairperson: Nerea Ubierna
X1.27
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EGU24-10052
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ECS
Kim Faassen, Ingrid Luijkx, Jordi Vilà-Guerau de Arellano, Raquel González-Armas, Bert Heusinkveld, Ivan Mammarella, and Wouter Peters

The ratios of atmospheric tracers are often used to interpret the local CO2 budget, where measurements at a single height are assumed to represent local flux signatures. Alternatively, these signatures can be derived from direct flux measurements or using fluxes derived from measurements at multiple heights. In this study, we contrast interpretation of surface CO2 exchange from tracer ratio measurements at a single height versus measurements at multiple heights. Specifically, we analyse the ratio between atmospheric O2 and CO2 (exchange ratio, ER) above a forest canopy. We consider two alternative approaches: the exchange ratio of the forest (ERforest) obtained from the ratio of the surface fluxes of O2 and CO2, derived from their vertical gradients measured at multiple heights, and the exchange ratio of the atmosphere (ERatmos) obtained from changes in the O2 and CO2 mole fractions over time measured at a single measurement height. We investigate the diurnal cycle of both ER signals, with the goal to relate the ERatmos signal to the ERforest signal and to understand the biophysical meaning of the ERatmos signal. We combined CO2 and O2 measurements from Hyytiälä, Finland during spring and summer of 2018 and 2019 with a conceptual land-atmosphere model and a theoretical relationship between ERatmos and ERforest to investigate the behaviour of ERatmos and ERforest during different environmental conditions. We show that the ERatmos signal rarely directly represents the forest exchange, mainly because it is influenced by entrainment of air from the free troposphere into the atmospheric boundary layer. The resulting ERatmos signal is not the average of the contributing processes, but rather an indication of the influence of large scale processes such as entrainment or advection. We conclude that the ERatmos only provides a weak constraint on local scale surface CO2 exchange, because large scale processes confound the signal. Single height measurements therefore always require careful selection of the time of day and should be combined with atmospheric modelling to yield a meaningful representation of forest carbon exchange. More generally, we recommend to always measure at multiple heights when using multi-tracer measurements to study surface CO2 exchange.

How to cite: Faassen, K., Luijkx, I., Vilà-Guerau de Arellano, J., González-Armas, R., Heusinkveld, B., Mammarella, I., and Peters, W.: Atmospheric O2 and CO2 measurements at a single height provide weak constraint on the surface carbon exchange., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10052, https://doi.org/10.5194/egusphere-egu24-10052, 2024.

X1.28
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EGU24-5556
Sergio Gurrieri and Roberto M.R. Di Martino

Climate change is intricately linked to the carbon cycle. Both phenomena are examined across various temporal and spatial scales to clarify the processes of carbon exchange between the atmosphere and the Earth's surface in response to increasing greenhouse gas emissions, primarily CO2. Anthropogenic CO2 emissions emerge as the main driver of global warming, while natural CO2 emissions into the atmosphere constitutes approximately 1% of annual CO2 emissions, mainly resulting from volcanic activity.

This study relies on datasets gathered during surveys at Etna volcano and the Madonie mountains, Italy, to identify spatial variations in stable isotope composition and the concentration of airborne CO2. The dataset was collected along a path specifically designed from the urban areas of Catania and Cefalù, both in Italy, to high altitudes (i.e., ~2200 m a.s.l.) at Mount Etna and the Madonie mountains, Italy, respectively. This dataset facilitates exploration of spatial variations in the sources of atmospheric CO2 and patterns in the isotopic composition and concentration of airborne CO2 with altitude.

The study's findings indicate that the primary sources of airborne CO2 exhibit a biogenic isotopic carbon signature at Etna and the Madonie mountains, although a more 13C-enriched CO2 source influences the isotopic signature of airborne CO2 at Mount Etna. The concentration of airborne CO2 and the carbon isotopic signature remain independent of altitude. However, a high correlation between altitude and oxygen isotopic signature suggests that variations in hydrology significantly impact the airborne CO2.

Furthermore, the study underscores the complex relationship between environmental variables and airborne CO2 concentration, indicating that the pattern in airborne CO2 cannot be comprehensively investigated solely through concentration analysis due to the high background CO2 concentration compared to relative spatial variations. Additionally, the carbon isotopic signature of CO2 enables the differentiation of multiple sources of CO2 at Mount Etna and the distinction of 13C-enriched volcanic CO2 from background air at low airborne CO2 concentrations.

How to cite: Gurrieri, S. and Di Martino, R. M. R.: Spatial Isotopic Analysis of Airborne CO2: Insights from Etna Volcano and Madonie Mountains, Italy, Surveys, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5556, https://doi.org/10.5194/egusphere-egu24-5556, 2024.

X1.29
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EGU24-20240
Naizhong Zhang, Ivan Prokhorov, Nico Kueter, Stefano Bernasconi, Mayuko Nakagawa, Alexis Gilbert, Yuichiro Ueno, Béla Tuzson, Lukas Emmenegger, and Joachim Mohn

Bulk isotope analytical methods of CH4 quantify carbon and hydrogen isotope ratios (δ13C and δD) to provide information on the sources and sinks of CH4 in natural environments. A more extensive tracing of CH4 pathways, especially when multiple processes and sources are involved, has been realized by novel measurements techniques capable of methane clumped isotope analysis (termed as Δ13CH3D and Δ12CH2D2) during the past decade. These paired datasets can either be used as proxy for exploring CH4 formation temperatures under thermodynamic equilibrium, or studying contributions of kinetically controlled processes during CH4 formation and consumption1.

Currently, methane clumped isotope analysis is performed by two different techniques: isotope-ratio mass spectrometry (e.g. 253 Ultra from Thermo Fisher Scientific2 or Panorama from Nu Instruments1) or laser absorption spectroscopy (e.g. QCLAS from Aerodyne Research3,4), both of which have demonstrated a precision better than 0.5‰ for Δ13CH3D and 1.5‰ for Δ12CH2D2, which is sufficient for most applications. This work will provide insights about the main instrumental features, measurement protocols and performance of the 253 Ultra HR-IRMS at Tokyo Institute of Technology (Japan)2,5, and the QCL absorption spectrometer at Empa (Switzerland)4. Furthermore, advantages and limitations of both techniques during current applications in natural methane samples are discussed. Finally, perspectives for future applications at low CH4 concentrations, such as atmospheric monitoring, are provided.

 

References:

  • Young et al., 2017, Geochimica et Cosmochimica Acta; 2. Dong et al., 2020, Thermo Scientific white paper; 3. Gonzalez et al., 2019, Analytical Chemistry; 4. Prokhorov and Mohn, 2022, Analytical Chemistry; 5. Zhang et al., 2021, Geochimica et Cosmochimica Acta

How to cite: Zhang, N., Prokhorov, I., Kueter, N., Bernasconi, S., Nakagawa, M., Gilbert, A., Ueno, Y., Tuzson, B., Emmenegger, L., and Mohn, J.: Pros and cons of methane clumped isotope analysis by high-resolution isotope-ratio mass spectrometry and laser absorption spectroscopy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20240, https://doi.org/10.5194/egusphere-egu24-20240, 2024.

X1.30
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EGU24-21410
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ECS
Santiago Botía, Shujiro Komiya, Sam P. Jones, Ingrid Chanca, Viviana Horna, Gisela Dajti, Getachew A. Adnew, Sipko Bulthuis, Jochen Schöngart, Maria Teresa Fernandez Piedade, Florian Wittmann, Daniel Magnabosco Marra, Michael Rothe, Heiko Mossen, Armin Jordan, Thomas Röckmann, Jost Lavric, Carlos Sierra, Susan Trumbore, and Hella van Asperen

The decreasing global trend in 𝛿13𝐶 − 𝐶𝐻4 suggests that rising biogenic sources of methane are a plausible explanation for the current methane atmospheric growth rate. Furthermore, tropical wetlands represent one of the largest sources of uncertainty in the global methane budget and the Amazon basin plays a crucial role in this context as approximately 20% of its area is annually flooded. However, the availability of methane isotopic composition data for tropical wetlands is scarce, undermining our understanding of these tropical sources.

In this study, we present results from two sampling campaigns during the dry season, one in September 2019 and the other in August 2022. During each campaign, we collected air samples at different locations within the area around the Amazon Tall Tower Observatory (ATTO), such as in a black-water seasonally flooded forest (i.e. igapó), in an upland swampy valley (i.e. baixio), at the Uatumã black-water river and on the 80-m tower located on the upland terra-firme forest at the ATTO site. Air samples were collected with pressurized glass flasks and pre-evacuated vials and were analyzed for the isotopic composition of methane (𝛿13𝐶 and 𝛿𝐷 ) with gas source isotope ratio mass spectrometer. We estimated isotopic source signatures of CH4 emissions from the four different sites using the intercept of an orthogonal fit in a Keeling plot.

Relative to the Amazon atmospheric background value of -59 ‰ per mill (Beck et al., 2012), our isotopic source signatures are more depleted in 𝛿13𝐶 ranging from -60 ‰ to -68 ‰, which confirms -as expected- a strong wetland-related biogenic source. Within this range, methane source signatures from areas near the Uatumã river (-68 ‰) and a periodically flooded valley (representing small streams of the region) have more depleted signatures (- 66 ‰). Using this range of source 𝛿13𝐶 signatures we explore the possibility of identifying different biogenic sources at the Tower based on continuous measurements (in-situ) of

𝛿13𝐶 − 𝐶𝐻4 and a Lagrangian atmospheric transport model to obtain the isotopic background (i.e. the isotopic signature of the air masses before entering the continent). Our results contribute valuable insights into the methane isotopic signature for different ecosystem types in central Amazonia, which could serve as a reference for measurement-based source attribution studies as well as a based on measurements and also for atmospheric transport modeling estimates.

How to cite: Botía, S., Komiya, S., Jones, S. P., Chanca, I., Horna, V., Dajti, G., Adnew, G. A., Bulthuis, S., Schöngart, J., Fernandez Piedade, M. T., Wittmann, F., Marra, D. M., Rothe, M., Mossen, H., Jordan, A., Röckmann, T., Lavric, J., Sierra, C., Trumbore, S., and van Asperen, H.: Characterization of the isotopic signature in methane from several biogenicsources in the central Amazon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21410, https://doi.org/10.5194/egusphere-egu24-21410, 2024.

X1.31
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EGU24-3338
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ECS
Xuechao Qin, Xinyuan Dong, Congqiang Liu, Rongfei Wei, Zhenghua Tao, Hua Zhang, and Qingjun Guo

Mercury (Hg) is highly toxic and the only heavy metal that can exist in the atmosphere in gaseous form. When atmospheric Hg mixes with aerosols, it forms particulate-bound mercury (PBM). PBM can be transported and settle down quickly across regions, posing serious threats to ecosystems globally. Despite these concerns, tracking the sources and transport of atmospheric Hg remains challenging due to its global dispersal nature. However, the three-dimensional fractionation of Hg isotopes provides a feasible approach for addressing this issue. In this study, PBM2.5 and PBMTSPsamples were collected simultaneously in rural, suburban, urban, industrial, and coastal areas of the Beijing-Tianjin-Hebei (BTH) region, which is influenced by severe atmospheric pollution and the East Asian monsoon. Due to the significant influence of anthropogenic sources, the concentrations of PBM2.5 and PBMTSP were highest in the industrial and coastal areas, followed by the urban, suburban, and rural areas. The δ202Hg values of PBM2.5 and PBMTSP at the five sites were negative, overlapping with the values of most anthropogenic sources. However, most PBM2.5 and PBMTSP samples showed significantly positive Δ199Hg, significantly higher than the values of emission sources,especially for PBM2.5. The mass-independent fractionation (MIF) of Hg and sulfur isotopes showed that strong photochemical reduction happened during long-distance transport, making Δ199Hg have a positive shift. The positive changes in Δ200Hg may be due to ozone-mediated oxidation during the transport process, as shown by the interesting relationships between O3, Δ199Hg, and Δ200Hg in PBM2.5. Additionally, the analysis of backward trajectories unveiled the influence of air masses originating northwest of the BTH region through high-altitude transport. The cross-border transport of PBM, influenced by westerly and northwesterly air masses from Central Asia and Russia, markedly impacted  PBM pollution in the BTH region. Furthermore, these air masses, upon reaching the BTH area, would transport heightened PBM concentrations to the ocean through the winter monsoon. Conversely, during the summer, southeastward air masses transported from the ocean by the summer monsoon acted to mitigate the inland PBM pollution. The study results show that significant positive odd-MIF of PBM can occur in places with intensive anthropogenic emissions rather than being limited to remote areas. It implies that the odd-MIF resulting from atmospheric transport has likely been significantly undervalued. Our research offers valuable perspectives on the transport, transformation, and circulation of Hg in the environment.

How to cite: Qin, X., Dong, X., Liu, C., Wei, R., Tao, Z., Zhang, H., and Guo, Q.: Mass-Independent Fractionation Reveals the Sources and Transport of Atmospheric Particulate Bound Mercury, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3338, https://doi.org/10.5194/egusphere-egu24-3338, 2024.

X1.32
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EGU24-548
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ECS
Amelia Bond, Markus M. Frey, Jan Kaiser, Alina Marca, and Freya Squires

Photolysis of snowpack nitrate results in emission of the reactive nitrogen species NOx and HONO. These are important pre-cursors of HOx radicals and ozone, and thereby affect the oxidising capacity of the lower atmosphere above remote snow-covered areas. This is of particular importance in the polar regions as the usual OH radical formation pathway (ozone photolysis and reaction of O(1D) with H2O) is limited by the low water vapour concentration. Isotope analysis of atmospheric reactive nitrogen species and snow nitrate is proving to be a crucial tool for elucidating mechanisms of reactive nitrogen cycling in and above snow.

The first snowpit profiles of nitrate stable isotopes (δ15N, δ18O) and concentration at Halley VI Research Station in coastal Antarctica will be presented. The observed isotope fractionation provides evidence of photochemical loss of nitrate and allows estimation of the photolytic isotope fractionation constant at the site. At this high accumulation site, the peak in nitrate concentration from the previous summer is preserved below the snow surface, unlike at low accumulation sites on the Antarctic Plateau. Combining measurements of nitrate concentration and its isotopic compositions preserved in snow helps disentangle the isotope signature of seasonal changes in atmospheric nitrate sources from post-depositional isotope fractionation occurring even at high snow accumulation sites.

How to cite: Bond, A., Frey, M. M., Kaiser, J., Marca, A., and Squires, F.: Isotope analysis of snowpack nitrate in coastal Antarctica; evidence of nitrate photolysis and preservation., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-548, https://doi.org/10.5194/egusphere-egu24-548, 2024.

X1.33
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EGU24-4515
Qingjun Guo, Xiaokun Han, Xinyuan Dong, Xuechao Qin, and Rongfei Wei

Air pollution has become a serious problem in some parts of the world. The mechanism of sulfate formation during haze events is still not clear. This research looks at the different sulfur isotope compositions of sulfate in PM2.5 (from 2015 to 2016) in Beijing and in seasonal samples of PM2.5, PM1.0, and TSP from rural, suburban, urban, industrial, and coastal areas of North China (in 2017). The goal is to figure out the mechanism by which SO2 oxidizes at different levels of air pollution. An obvious seasonal variation (with positive values in spring, summer, and autumn and negative values in winter) is shown by the Δ33S values of sulfate in aerosols, except for those samples collected in rural areas. The Δ33S value (S-MIF) of sulfate in PM2.5 shows a pronounced seasonality, with positive values in spring, summer, and autumn and negative values in winter. The negative Δ33S changes that happen during winter haze events are mostly caused by SO2 being oxidized by H2O2 and transition metal ion catalysis (TMI) in the troposphere, which is most likely caused by coal burning. The positive Δ33S results observed on clean days are mainly attributed to tropospheric SO2 oxidation and stratospheric SO2 photolysis. These results provide important information on sulfate formation during haze events and clean days.

How to cite: Guo, Q., Han, X., Dong, X., Qin, X., and Wei, R.: Sulfate formation in haze pollution using multiple sulfur isotopes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4515, https://doi.org/10.5194/egusphere-egu24-4515, 2024.

X1.34
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EGU24-13866
Akshay Nataraj, Susan Fortson, Frederic Despagne, Julio Lobo Neto, and Doug Baer

Stable isotope analysis of water 2H2O and H218O are powerful tracers to understand the different hydrological processes like ecohydrological processes, and hydroclimatic processes [1]. The measurement of δ2H and δ18O in water samples using laser-based absorption techniques is adopted increasingly in hydrologic and environmental studies. In contrast to the conventional Isotope ratio mass spectrometry (IRMS) technique, optical absorption spectroscopic techniques allow the realization of isotopologue-specific, non-destructive, and compact spectrometers with short analysis times with high-precision capabilities.

ABB’s ultraportable water analyzers are compact, portable field-deployable laser spectrometers capable of making continuous, high-frequency measurements of δ18O and δ2H from multiple water sources. The instrument is based on Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) technique [2]. These analyzers are capable of measuring liquid water (GLA132-LWIA) or vapor (GLA132-WVIA).  They are rugged and designed to handle both natural and isotopically enriched water samples.  Users can leverage the precision and speed of the GLA132-LWIA by coupling it with a portable auto-injector to perform automated, unattended injection patterns on multiple samples.

An important asset of this innovative approach based on OA-ICOS technology coupled with the portable auto-injector technology is its sample throughput, which allows one to measure approximately 90 samples a day corresponding to 720 injections each with a sample volume of 0.5 µL per injection per day. The precision (1σ) achieved corresponds to 0.6 ‰ for δ2H and 0.2 ‰ for δ18O. The analyzer’s ease of use, field portability, durability, and high throughput make it an excellent choice for reliable, high-performance measurement of freshly collected samples in the field, thereby opening a plethora of applications to understand the different processing governing the earth’s climate.

[1] Tian, C.,et al., Sci Rep 8, 6712 (2018). https://doi.org/10.1038/s41598-018-25102-7

[2] A. O’Keefe, et al., Chemical Physics Letters, vol. 307, no. 5, pp. 343–349, Jul. 1999, doi: 10.1016/S0009-2614(99)00547-3.

How to cite: Nataraj, A., Fortson, S., Despagne, F., Lobo Neto, J., and Baer, D.: Laser absorption spectroscopy-based ultraportable analyzer for δ18O and δ2H in water., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13866, https://doi.org/10.5194/egusphere-egu24-13866, 2024.

X1.35
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EGU24-7270
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ECS
Davide Iazzetta and Mauro Rubino

We present a project aiming to provide a new estimate of the parameter known as "climate sensitivity" (symbol γL in the models) which is essential to constrain models of future climate change. This parameter describes how the amount of carbon sequestered by terrestrial ecosystems depends on temperature. Predictions of future climate by models show significant uncertainties associated with the estimates of carbon sequestration by terrestrial ecosystems with future temperature increases. Quantifying γL with data measured in the industrial era is very complicated because the terrestrial part of the carbon cycle is dominated by the effect of the increase in atmospheric CO2 (the so-called anthropogenic “fertilization” or CO2 concentration feedback, symbol βL in the models), while the effect of temperature is smaller. We will derive γL from measurements of ultra-trace gases trapped in polar ice cores in pre-industrial times.

The Little Ice Age (i.e. the period that roughly covers the centuries 1400-1800 AD) was characterized by temperatures lower than the average of the last millennium, due to intense volcanic activity and reduced solar activity. The global decrease in temperature has coincided with a decrease in the atmospheric concentration of CO2, mainly caused by sequestration from terrestrial ecosystems. Low CO2 concentrations contributed negligibly to the decrease in temperature, making the Little Ice Age a suitable time to derive γL.

Why CO2 decreased during the Little Ice Age is debated. On the one hand, considerations deriving from models that simulate the amount of carbon present in terrestrial ecosystems suggest that primary productivity increased during the Little Ice Age because of an anthropogenic effect. This increase would have been caused by pandemics and colonial conquests in America which led to a depopulation of cultivated lands and a regrowth of tree species. On the other hand, measurements of carbonyl sulphate (COS) and numerical calculations capable of closing the COS budget suggest that primary productivity naturally decreased during the Little Ice Age. In this second case, the decrease in CO2 would be caused by the fact that the respiration of terrestrial ecosystems decreased to a greater extent than the decrease in primary productivity. Therefore, if this second hypothesis is correct, it would be possible to derive γL from COS data covering the Little Ice Age.

Unfortunately, COS measurements covering the Little Ice Age have great uncertainty. It is therefore necessary to carry out new measurements of COS concentration during the Little Ice Age. The COS measurements will be accompanied by CO2 and δ13C-CO2 measurements, necessary to confirm, on the one hand, the working hypothesis, and, on the other, the quality of the ice samples used. Finally, future developments could build on measurements of COS isotopes in ice samples.

Rubino M., et al. Terrestrial uptake due to cooling responsible for low atmospheric CO2 during the Little Ice Age, Nature Geoscience, 9, 691-694 (2016)

How to cite: Iazzetta, D. and Rubino, M.: Quantification of the climate sensitivity of terrestrial ecosystems through the analysis of ultra-trace gases in ice cores over the last millennium, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7270, https://doi.org/10.5194/egusphere-egu24-7270, 2024.

X1.36
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EGU24-10688
Nerea Ubierna, Sophie L. Baartman, María Elena Popa, Jérôme Ogée, Maarten C. Krol, and Lisa Wingate

Anthropogenically emitted CO2 is warming the earth’s climate to temperatures that already exceed pre-industrial levels by more than 1.2 oC. Terrestrial vegetation has slowed the rate of climate change by removing part of this anthropogenic emission. Accurate estimations of the present and future terrestrial carbon sink are still needed for forecasting climate and for informing policies for climate stabilization. This requires precise knowledge of the photosynthetic C uptake over land (gross primary production, GPP), independently of the C released through plant and soil respiration. The gas carbonyl sulfide (COS) has emerged as a promising tracer for GPP. This is because both CO2 and COS are a substrate for carbonic anhydrase (CA), the first enzyme involved in photosynthesis, so that the uptake by foliage of COS and CO2 often covaries. Estimating GPP from COS measurements and atmospheric budgets also requires quantifying ocean and industrial COS sources, which is challenging. Isotopic constrained COS tropospheric mass balances can help quantify the relative contribution of these sources if the isotope discrimination during COS uptake by terrestrial vegetation (the main COS sink) is known. However, little is known about plant-atmosphere COS isotope exchange; measurements are challenging and theory to interpret these measurements is limited. Herein, we present a new comprehensive model for discrimination during COS uptake by plants (∆34S) and use it to revisit existing COS isotope datasets and atmospheric budgets. Our ∆34S model expands Davidson et al. (2022) pioneer framework by accounting for leaf COS production. By analogy with the well-established model for photosynthetic discrimination against 13CO2, Davidson et al. ∆34S model stated that COS discrimination occurs as COS diffuses into the leaf and binds to CA. Leaf COS emission was not considered, although it has been reported in species ranging from bryophytes to wheat and trees. Because it is uncertain where these emissions occur, we tested different leaf-level COS emission scenarios - including zero emissions - in various leaf compartments (cuticle, intercellular space, cytosol), alone or in combination. We used this comprehensive model to generate predictions for ∆34S in C3 and C4 species and discussed implications for determining a global plant uptake fractionation factor. Our mechanistic model provides a framework to interpret vegetation-atmosphere COS isotope exchange that can prove useful to improve COS uptake-based GPP estimates and our understanding of plant function, especially when combined with other isotopes (C, O, H).

How to cite: Ubierna, N., Baartman, S. L., Popa, M. E., Ogée, J., Krol, M. C., and Wingate, L.: A comprehensive model for COS isotope discrimination during leaf COS uptake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10688, https://doi.org/10.5194/egusphere-egu24-10688, 2024.

X1.37
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EGU24-16015
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ECS
Felix M. Spielmann, Albin Hammerle, Katharina Scholz, Gil Putz, Lorenz Hänchen, Anna De-Vries, and Georg Wohlfahrt

The gross primary productivity (GPP), which represents the gross uptake of carbon dioxide (CO2) by plants, cannot be directly measured at the ecosystem level. It must instead be inferred either by applying models or by measuring proxies. A notable proxy is the trace gas carbonyl sulfide (COS), which is particularly interesting because it follows a pathway into plant leaves similar to CO2 and, unlike CO2, is generally not reemitted.

To utilize COS as a tracer for GPP, the leaf relative uptake (LRU)—the ratio of the deposition velocities of COS to CO2 at the leaf level—must be known a priori. Initial studies suggested that LRU values were relatively constrained, around 1.7. However, it has been observed that LRU varies between plant species and is influenced by environmental factors such as drought, vapor pressure deficit (VPD), and photosynthetically active radiation (PAR).

The variation in LRU related to PAR is due to COS primarily being catalyzed by the enzyme carbonic anhydrase in a light-independent reaction, contrasting with CO2 uptake via photosynthesis, which is dependent on PAR. Consequently, LRU increases under lower light conditions, even when stomatal control on both gases is similar.

This light dependency prompts questions about LRU variation within canopies. While most LRU chamber measurements have been conducted under laboratory conditions or in canopy crowns, additional data on LRU variability within canopies, particularly in lower light conditions, are necessary. A comprehensive understanding of LRU, encompassing both crown and shadow-adapted leaves at various canopy positions and considering stand species composition, is essential for accurately calculating GPP at the ecosystem scale using eddy covariance (EC) measurements.

To investigate how LRU varies within the canopy, particularly in response to environmental factors like PAR and VPD, and to compare the LRUs from different chamber measurements to EC measurements, we conducted a measurement campaign in an Austrian Pine forest. This included ongoing eddy covariance measurements of COS, CO2, and H2O, supplemented by manual measurements of the same gases using branch chambers at three levels within the Pinus sylvestris canopy and three additional chambers of Juniperus communis.

Above 400 µmol photons m² s PAR, where we consider the LRU to be light independent, the LRU reached 1.61±0.3 at the top of the crown and decreased to 1.55±0.4 and 1.56±0.3 going consecutively deeper into the canopy of Pinus sylvestris. In contrast, the LRU of Juniperus communis in the understory was notably lower, at 1.41±0.4. Between 100 and 400 µmol photons m² s PAR, the LRUs increased to 1.81±0.3 and 1.69±0.5 for the upper and middle canopy layers, respectively, while decreasing to 1.43±0.2 and 1.19±0.2 in the lower parts of Pinus sylvestris and Juniperus communis, respectively. This decrease in LRU deeper within the canopy is attributed to a greater reduction in COS compared to CO2 deposition velocity of the leaves. The median LRU above 800 µmol photons m² s PAR, based on classical daytime flux partitioning for the summer month of 2022, was 2.5±0.7, indicating the need for further investigation into the observed discrepancy in LRU.

How to cite: Spielmann, F. M., Hammerle, A., Scholz, K., Putz, G., Hänchen, L., De-Vries, A., and Wohlfahrt, G.: From over to under, a story about the vertical within-canopy variation of the leaf relative uptake rate of COS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16015, https://doi.org/10.5194/egusphere-egu24-16015, 2024.