Stable isotopes and other novel tracers, such as carbonyl sulfide (COS) and clumped isotopes, help to identify and quantify biological, chemical and physical processes that drive Earth's biogeochemical cycling, atmospheric processes and biosphere-atmosphere exchange. Recent developments in analytical measurement techniques now offer the opportunity to investigate these tracers at unprecedented temporal and spatial resolution and precision.
This session includes contributions from field and laboratory experiments, latest instrument developments as well as theoretical and modelling activities that investigate and use the isotope composition of light elements (C, H, O, N) and their compounds as well as other novel tracers for biogeochemical and atmospheric research.
Topics addressed in this session include:
- Stable isotopes in carbon dioxide (CO2), water (H2O), methane (CH4) and nitrous oxide (N2O)
- Novel tracers and biological analogues, such as COS
- Polyisotopocules ("clumped isotopes")
- Intramolecular stable isotope distributions ("isotopomer abundances")
- Analytical, method and modelling developments
- Flux measurements
- Quantification of isotope effects
- Non-mass dependent isotopic fractionation and related isotope anomalies
vPICO presentations: Tue, 27 Apr
Leaf water becomes enriched in heavier isotopes during transpiration, with the degree of enrichment dependent on evaporative conditions. However, there has been considerable uncertainty regarding the importance of gradients in isotope enrichment within leaves (i.e. a Péclet effect). That is, experimental studies show that evidence is approximately equally divided between the Péclet effect being important and being irrelevant for leaves. Our recent work demonstrates a link between the hydraulic design of leaves and the presence or otherwise of a Péclet effect. That is, with prior knowledge of the pathways of water movement through leaves, the most appropriate modelling framework can be selected and uncertainty in interpretation and prediction reduced.
Reducing uncertainty is important because the H218O composition of leaves is passed on to oxygen atoms in O2 and CO2 so terrestrial plants strongly influence isotopic composition of the atmosphere. Of particular interest is the interpretation of the Dole effect, the oxygen isotopic imbalance between atmospheric O2 and seawater. The ice core record of the Dole effect has been interpreted as an integrative proxy for the global balance between terrestrial and oceanic productivity, or more recently as an indication of the migration of terrestrial productivity towards and away from the equator. Both interpretations depend on highly uncertain leaf water isotope enrichment models. In light of the link between leaf hydraulic design and the Péclet effect, should we expect differences between species in the 18O of O2 produced by photosynthesis? Do we need to reinterpret the Dole effect?
How to cite: Barbour, M.: Leaf hydraulic design influences the development of isotope gradients in leaves, but are there subsequent effects on isotopes of atmospheric oxygen?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10413, https://doi.org/10.5194/egusphere-egu21-10413, 2021.
High precision measurements of triple isotopic composition of oxygen in the air trapped in ice cores is a useful tool to infer the global gross biosphere productivity in the past. The isotopic composition of oxygen is influenced by many physical, chemical and biological processes during consumption and production of oxygen by the oceanic and terrestrial biosphere. For an accurate quantification of the past biosphere productivity, it is thus important to determine the different fractionation processes occurring in the biosphere during respiration and photosynthesis processes.
We present here quantification of fractionation coefficients associated with δ180 and the D170 of 02 during respiration and photosynthesis within the terrestrial biosphere. The experimental set-up relies on closed biological chambers in which all the environmental parameters are controlled and measured. Triple isotopic composition of oxygen is regularly measured through sampling of small aliquots at a low frequency (4 h to 4 days). Seven 2-month long experiments were performed in order to check the reproducibility of our set-up and quantify uncertainty on the determination of the fractionation coefficients.
In order to improve our set-up for future experiments using different plants, we also present perspectives for a continuous measurement of the isotopic composition of oxygen using optical spectroscopy (Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS) technique). This instrument is currently being characterized and we will present its current performances.
Triple isotopic composition of oxygen in the atmospheric dioxygen to reconstruct the dynamic of global biosphere productivity in the past from measurements in biological chambers.
How to cite: Paul, C., Farradèche, M., Piel, C., Sauze, J., Romanini, D., Pasquier, N., Prié, F., Jacob, R., Jossoud, O., Dapoigny, A., Devidal, S., Milcu, A., and Landais, A.: Triple isotopic composition of oxygen in the atmospheric dioxygen to reconstruct the dynamic of global biosphere productivity in the past from measurements in biological chambers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7853, https://doi.org/10.5194/egusphere-egu21-7853, 2021.
How to cite: Ogee, J., Hirl, R., Ostler, U., Schäufele, R., Baca Cabrera, J., Zhu, J., Schleip, I., Wingate, L., and Schnyder, H.: Temperature-sensitive biochemical 18O-fractionation and humidity-dependent attenuation factor of leaf water 18O-enrichment are needed to predict 18O composition of cellulose, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15584, https://doi.org/10.5194/egusphere-egu21-15584, 2021.
Statistical evaluation of the correlation pattern between rising global temperature and stable water isotopes in precipitation.
Lukas Ditzel, Jonas Schramm, Matthias Gassmann
Department of Hydrology and Substance Balance, University of Kassel, Kurt-Wolters-Strasse 3, 34125 Kassel, Germany
Stable water isotopes in precipitation on the northern hemisphere are usually following a predictable pattern throughout the year, with high amounts in summer and low amounts of deuterium and 18O in the winter season. Backed by a richness of available date from the International Atomic Energy Agency (IAEA), one can mostly expect an annual sinusoidal form of isotope data, when looking at data for a certain region in the northern hemisphere.
Since the driving factor for isotopic enrichment or depletion is isotopic fractionation, the seasonal behavior is strongly correlated to air-temperature. The correlation between temperature and fractionation is strong enough to explain most of the greater deviations from the sinusoidal form like in arid regions. It occurs that globally rising temperatures, initiated by climate change, should have an impact on the sinusoidal form of the stable water isotope time series. We assumed, that rising temperatures will lead to higher contents of deuterium and 18O in the precipitation of the northern hemisphere. Due to the availability of data and the long time series, which are needed for robust answers, we focused our work on European and North-American data. First analyses showed a positive correlation between rising air-temperatures and isotopic content, but not all regions. Other effects like the elevation- and continental-effect were dampening the effect of rising global temperatures, especially in coastal regions or islands such as Ireland. More continental regions, however, are showing a rise for isotopic enrichment in precipitation. We analyzed this trend by the calculation of the trend-components of these time-series via Loess and validated them by using the Mann-Kendall-Test. Furthermore, we separated sets of data into monthly clusters and looked for rising temperature trends in every month over the size of the available time series. This second analysis was performed for the time series from weather stations in Berlin, Vienna and Krakow covering almost 40 years of monthly isotope data.
How to cite: Ditzel, L., Schramm, J., and Gaßmann, M.: Statistical evaluation of the correlation pattern between rising global temperature and stable water isotopes in precipitation., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15725, https://doi.org/10.5194/egusphere-egu21-15725, 2021.
The stable water isotopes (SWIs) (δ18O and δD) are used as an indicator of the intensity of the atmospheric hydrological cycle due to their large variability in time and space. Although data about vapor isotope ratio with high frequency and high resolution are now available by satellite observations and spectroscopic analyses, there is some room for discussion on the variability of isotope ratios in vapor and precipitation related to cloud microphysical processes.
Here, we incorporated SWI tracer into the latest version of a global cloud system resolving model (the Nonhydrostatic Icosahedral Atmospheric Model (NICAM)), iso-NICAM, and investigated the contribution of cloud microphysical processes to the variability of isotope ratios in precipitation and vapor. One of the merits used NICAM is that its physical process can cover from low spatial resolution to high spatial resolution. We conducted two mode simulations (GCM and CRM). The GCM mode simulation is based on the Arakawa-Schubert scheme as convective parameterization and a large-scale condensation scheme as the cloud physical process. In contrast, the CRM mode simulation is based on the a single-moment bulk cloud microphysics scheme with 6 water categories as cloud microphysical scheme, convective parameterization scheme was not used. These simulations are set to about 223 km of horizontal mesh resolution and 78 vertical layers. We conducted an AMIP-type climate experiment for one year from 1979.
The simulated precipitation δ18O showed the latitude effect pattern (high δ18O in low latitude region, low δ18O in high latitude region), but those values in the CRM mode was slightly lower than that in the GCM mode . The simulated precipitation δ18O in the CRM mode was lower in high altitude or inland regions compared with those in the GCM mode . Besides, the precipitation d-excess in the CRM mode shows large spatial variability compared with the GCM mode. Although the low spatial resolution was set in this study, these simulations indicated cloud microphysical processes are important for understanding the variability of isotope physics. We will conduct these simulations with finer spatial resolution and a more extended simulation period.
How to cite: Tanoue, M., Takano, Y., Yoshimura, K., and Yashiro, H.: Stable isotopes in precipitation and water vapor simulated by isotope-incorporated NICAM, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9376, https://doi.org/10.5194/egusphere-egu21-9376, 2021.
The hydrogen isotope composition (δ2H) of cellulose has been used to assess ecohydrological processes and carries metabolic information, adding new understanding to how plants respond to environmental change. However, experimental approaches to isolate drivers of δ2H variation is limited to the Yakir & DeNiro model (1990), which is difficult to implement and largely unvalidated. Notably, the two biosynthetic fractionation factors in the model, associated with photosynthetic (εA) and post-photosynthetic (εH) processes are currently accepted as constants, and the third parameter – the extent to which organic molecules exchange hydrogen (fH) with local water – is usually tuned in order to resolve the difference between modelled and observed cellulose δ2H values. Thus, by virtue, the metabolically interpretable parameter is only fH, whilst from theory, metabolic flux rates will also impact on the apparent fractionations. To overcome part of this limitation, we measured the δ2H of extracted leaf sucrose from fully-expanded leaves of seven species and a phosphoglucomutase ‘starchless’ mutant of tobacco to estimate the isotopic offset between sucrose and leaf water (εsucrose). Sucrose δ2H explained ~60% of the δ2H variation observed in cellulose. In general, εsucrose was higher (range: -203‰ to -114‰; mean: -151 ± 21‰) than the currently accepted value of -171‰ (εA) reflecting 2H-enrichment downstream of triose-phosphate export from the chloroplast, with statistical differences in εsucrose observed between species estimates. The remaining δ2H variation in cellulose was explained by species differences in fH (estimated by assuming εH = +158‰). We also tested possible links between model parameters and plant metabolism. εsucrose was positively related to dark respiration (R2=0.27) suggesting an important branch point influencing sugar δ2H. In addition, fH was positively related to the turnover time (τ) of water-soluble carbohydrates (R2=0.38), but only when estimated using fixed εA = -171‰. To decipher and isolate the “metabolic” information contained within δ2H values of cellulose it will be important to assess δ2H values of non-structural carbohydrates so that hydrogen isotope fractionation during sugar metabolism can be better understood. This study provides the first attempt at such measurements showing species differences in both source and sink processes are important in understanding δ2H variation of cellulose.
How to cite: Holloway-Philips, M., Baan, J., Nelson, D., Tcherkez, G., and Kahmen, A.: Measurements of leaf sucrose to explain variability in hydrogen isotope composition of leaf cellulose, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8918, https://doi.org/10.5194/egusphere-egu21-8918, 2021.
Water vapor has a fundamental role in weather and climate, being the strongest natural greenhouse gas in the Earth’s atmosphere. The main source of water vapor in the atmosphere is ocean evaporation, which transfers a large amount of energy via latent heat fluxes. In the past, evaporation was intensively studied using stable isotopes because of the large fractionation effects involved during water phase changes, providing insights on processes occurring at the air-water interface. Current theories describe evaporation near the air-water interface as a combination of molecular and turbulent diffusion processes into separated sublayers. The importance of those two sublayers, in terms of total resistance to vapor transport in air, is expected to be dependent on parameters such as moisture deficit, temperature and wind speed. Non-equilibrium fractionation effects in isotopic evaporation models are then expected to be related to these physical parameters. In the last 10 years, several water vapor observations from oceanic expeditions were focused on the impact of temperature and wind speed effect, assuming the influence of those parameters on non-equilibrium fractionation in the marine boundary layer. Wind speed effect is expected to be small on total kinetic fractionation and was discussed at length but was not completely ruled out. With a gradient-diffusion approach (2 heights above the ocean surface) and Cavity Ring-Down Spectroscopy we have estimated non-equilibrium fractionation factors for 18O/16O during evaporation, showing that the wind speed effect can be detected and has no significant impact on kinetic fractionation. Results obtained for wind speeds between 0 and 10 m s-1 in the North Atlantic Ocean are consistent with the Merlivat and Jouzel (1979) parametrization for smooth surfaces (mean ε18=6.1‰). A small monotonic decrease of the fractionation parameter is observed as a function of 10 m wind speed (slope ≅ 0.15 ‰ m-1 s), without any evident discontinuity. However, depending on the data filtering approach it is possible to highlight a rapid decrease of the kinetic fractionation factor at low wind speed (≤ 2.5 m s-1). An evident decrease of fractionation factor is also observed for wind speeds above 10 m s-1, allowing to hypothesize the possible effect of sea spray in net evaporation flux. Considering the average wind speed over the oceans, we conclude that a constant kinetic fractionation factor for evaporation is a more simple and reasonable solution than a wind-speed dependent parametrization.
Merlivat, L., & Jouzel, J. (1979). Global climatic interpretation of the deuterium‐oxygen 18 relationship for precipitation. Journal of Geophysical Research: Oceans, 84(C8), 5029-5033.
How to cite: Zannoni, D., Steen-Larsen, H. C., Peters, A., and Sveinbjörnsdóttir, Á. E.: Kinetic effects during ocean evaporation: observed relationship with wind speed , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5516, https://doi.org/10.5194/egusphere-egu21-5516, 2021.
We demonstrate the possibilities for continuous high precision in situ measurements of δ13C(CH4) and δ2H(CH4) for understanding regional CH4 emissions and explain how advances in nascent measurement techniques looking at ‘clumped’ CH4 might improve our understanding on the global scale.
‘Boreas’ is a new fully automated sample-preparation coupled dual laser spectrometer system developed at the National Physical Laboratory, able to make accurate and precise simultaneous measurements of δ13C(CH4) and δ2H(CH4) through the measurement of isotopologue ratios of CH4. Average daily repeatabilities of <0.08 ‰ for δ13C (n=10, 1 SD) and <1‰ δ2H of a compressed ‘background’ air sample (1.9 ppm dry air amount fraction CH4) are achieved, making the measurements comparable to bulk isotope ratio mass spectrometry. These measurements are interspersed with air sample measurements from the roof of our building in west London, and we show the possibility to differentiate potential sources of CH4 under different meteorological conditions.
We use a particle dispersion model (the Met Office’s NAME) and inverse method to predict the possible impact of the new continuous isotope ratios measurements on quantification of emissions from individual source sectors, should the technique be deployed to a tall tower network of monitoring sites in the UK.
Finally, our theoretical analysis is extended beyond the most abundant isotopologues of CH4 to look at how analysis of the clumped isotopes might be able to impact our understanding of interannual variability in the global CH4 burden. We incorporate measurements from emission sources and information on reaction rates into a global box model (with an inverse method) to show the added value of strategic ∆CH2D2 and ∆13CH3D ambient air measurements relative to bulk isotope ratios alone.
How to cite: Rennick, C., Chung, E., Arnold, T., Safi, E., Drinkwater, A., Dylag, C., Mussell Webber, E., Pearce, R., Lowry, D., and Manning, A.: Novel stable isotopic measurements for understanding atmospheric methane, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15547, https://doi.org/10.5194/egusphere-egu21-15547, 2021.
We present the first spatially varying map of the δD-CH4 signature of wetland methane emissions and model its impact on atmospheric δD-CH4. The δD-CH4 signature map is derived by relating the δD-H2O of precipitation to the measured δD-CH4 of methane wetland emissions at a variety of wetland types and locations. Since the δD-H2O of precipitation is highly latitude-dependent, including this spatial variation has the potential to have a large impact on the distribution of δD-CH4 observed in the atmosphere. This latitude-dependence means that wetland emissions at different latitudes can have very different impacts on atmospheric δD-CH4, which could provide a useful way to constrain the location of wetland methane emissions in future inverse modelling studies. Here, we assess the implications for model studies on the differences that arise by treating δD-CH4 wetland source signatures as globally uniform rather than accounting for the large spatial variation. We also assess the potential for δD-CH4 to provide an independent constraint on wetland emissions over the more abundant and widely measured δ13C-CH4.
How to cite: Stell, A., Douglas, P., Rigby, M., and Ganesan, A.: The impact of spatially varying wetland source signatures on the atmospheric variability of dD-CH4, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12630, https://doi.org/10.5194/egusphere-egu21-12630, 2021.
Clumped isotope analysis is a powerful tool to constrain methane's origin in various geological, biogeochemical, and environmental settings. The extremely low abundance of 12CH2D2 and 13CH3D isotopologues poses a challenge for the existing analytical systems. Mole fraction enhancement and cleaning of the environmental samples are necessary to fully exploit the potential of modern analyzers, requiring 50 to 1000 μmol of pure CH4. To enable high-precision Δ12CH2D2 and Δ13CH3D analysis with dual-QCL (8.6 μm and 9.3 μm) absorption spectroscopy in a multipass cell (400 m), we have developed a new automated cryogen-free unit for methane Cleaning and Extraction – CleanEx.
The unit can process up to 18 liters of sample air at a high flow rate of 900 ml min−1. Methane (TBP = −161 °C) is separated from major air components on a high capacity trap filled with HayeSep D (Trap 1, −176 °C). Sequential desorption and transfer to a second trap (Trap 2, −181°C) ensure complete O2 and Ar removal. Substances with a higher boiling point, i.e., CO2, N2O, H2O, CnHm, remain on Trap 1 to be removed at a later conditioning phase. CleanEx demonstrates equal performance for gas mixtures with initial methane mole fraction ranging from 2 ppm up to 2%. In contrast to the previously developed single trap TREX system (Eyer et al., 2016), atmospheric O2 and Ar are effectively separated by cryo-focusing of CH4 on the second trap. Ongoing work is focused on the separation of atmospheric gases with boiling points close to methane, e.g., Kr (TBP = −153 °C).
We present the instrument design, performance, and details of its operation. Fractionation effects, methane recovery efficiency, and implications for high-precision δ13C-CH4, δD-CH4, Δ13CH3D, and Δ12CH2D2 analyses are being discussed.
Acknowledgments. This work was supported by the Swiss National Science Foundation (SNSF) under R'Equip project QCL4CLUMPS (no. 206021_183294) and the project STELLAR (grant no. 19ENV05; Stable isotope metrology to enable climate action and regulation) which has received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme.
Eyer, S., Tuzson, B., Popa, M. E., van der Veen, C., Röckmann, T., Rothe, M., Brand, W. A., Fisher, R., Lowry, D., Nisbet, E. G., Brennwald, M. S., Harris, E., Zellweger, C., Emmenegger, L., Fischer, H., and Mohn, J.: Real-time analysis of δ13C- and δD-CH4 in ambient air with laser spectroscopy: method development and first intercomparison results, Atmos. Meas. Tech., 9, 263–280, https://doi.org/10.5194/amt-9-263-2016, 2016.
How to cite: Prokhorov, I. and Mohn, J.: Cryogen-free fully automated preconcentration unit to enable Δ13CH3D and Δ12CH2D2 analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-132, https://doi.org/10.5194/egusphere-egu21-132, 2021.
Due to the potential to fingerprint emissions, carbon stable isotopes are considered a powerful tool to get insight into sources of air pollutants and to study their atmospheric life cycle. Including the independent isotopic knowledge into chemical models, not only concentration but also isotope ratios can be predicted. This provides the possibility to differentiate the impact of source strength from that of chemical reactions in the atmosphere. In a recent study comparing Lagrangian-particle-dispersion-simulations with ambient observations, Betancourt et al.  (ACPD2020) found that the observed isotopic age of levoglucosan, a biomass burning tracer, agrees well with the isotopic age derived from back-plumes analyses. This showed that the wintertime aerosol burden from domestic heating observed in residential areas of North-Rheine-Westphalia, Germany, is of local or regional origin. Error analyses though indicated that the largest source of uncertainty was the limited information on emission isotope ratios.
In this work, the stable isotope ratios of levoglucosan in aerosol particles emitted from the combustion of 18 different biomass fuels typically used for domestic heating in Western and Eastern Europe (soft and hard woods, brown coals and corn cobs, respectively) were measured by Thermal Desorption- Two-Dimensional Gas Chromatographie- Isotope Ratio Mass Spectrometry (TD-2DGC-IRMS). Additionally to the compound specific measurements, isotopic ratios of total carbon in the fuel parent material, in the precursor cellulose, as well as in sampled aerosol particles were determined.
Levoglucosan δ13C was found to vary between -23.6 and -21.7‰ for the C3 plant samples, showing good agreement with Sang et al  (EST2012). The brown coal and the C4 plant samples were isotopically heavier, showing isotopic ratios in the range of -21,1 to -18.6‰ and -12.9‰, respectively. In this presentation, the observed levoglucosan δ13C will be discussed with respect to the carbon isotopic composition of the parent materials. The potential of using compound specific δ13C measurements of levoglucosan for improved source apportionment will be addressed.
How to cite: Khundadze, N., Küppers, C., Kammer, B., Garbaras, A., Masalaite, A., Wissel, H., Luecke, A., Kiendler-Scharr, A., and Gensch, I.: Benchmarking source specific isotopic ratios of levoglucosan to better constrain the contribution of domestic heating to the air pollution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10342, https://doi.org/10.5194/egusphere-egu21-10342, 2021.
Anthropogenic activities, particularly fertilisation, have resulted in significant increases in reactive nitrogen (rN) in soils globally, leading to eutrophication, acidification, poor air quality, and emissions of the important greenhouse gas N2O. Understanding the partitioning of rN losses into different environmental compartments is critical to mitigate negative impacts, however, loss pathways are poorly quantified, and potential changes driven by climate warming and societal shifts are highly uncertain. We present a coupled soil-atmosphere isotope model (IsoTONE; ISOtopic Tracing Of Nitrogen in the Environment) to partition rN losses into leaching, harvest, NH3 volatilization, and production of NO, N2 and N2O based on a global dataset of soil δ15N, as well as numerous other geoclimatic and experimental datasets. The model was optimized in a Bayesian framework using a time series of N2O mixing ratios and isotopic compositions since the preindustrial era, as well as a global dataset of N2O emission factors (EF). The posterior model results showed that the total anthropogenic flux in 2020 (7.8 Tg N2O-N a-1) was dominated by indirect emissions resulting from N deposition, while the growth rate and trend in anthropogenic N2O was driven by both direct N fertilisation and deposition inputs. In contrast, inputs from fixation N drive natural N2O emissions, and were responsible for subdecadal interannual variability in total emissions.
Total N gas (N2O + NO + N2) production and N2O losses were strongly dependent on geoclimate and thus spatially variable, therefore the spatial pattern of N inputs strongly impacted resulting EFs and total N2O emissions. The area-weighted global EF for N2O was 1% of anthropogenic N inputs in 2020, similar to the current IPCC default of 1.4%, however the N input-weighted global EF was 4.3%. Shifts in fertilisation inputs from the temperate Northern hemisphere towards warmer regions with higher EFs such as India and China have led to accelerating N2O emissions (1.02±0.7 Tg N2O-N a-1). In addition, N2O emissions have increased over the past decades due to climate warming (0.76±0.4 Tg N2O-N a-1). Predicted increases in fertilisation in India and Africa in the coming decades could further accelerate N2O-driven climate warming, unless mitigation measures are implemented to increase fertiliser N use efficiency and reduce N2O emission factors.
How to cite: Harris, E., Yu, L., Wang, Y. P., Mohn, J., Bai, E., Barthel, M., Six, J., Bauters, M., Boeckx, P., Dorich, C., Farrell, M., Henne, S., Krummel, P., Loh, Z., Steinbacher, M., Zellweger, C., Wells, N. S., Bahn, M., and Rayner, P.: Spatial changes in nitrogen inputs drive short- and long-term variability in global nitrous oxide emissions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-804, https://doi.org/10.5194/egusphere-egu21-804, 2021.
Urban polar areas can be subject to severe pollution in winter, linked to sharp temperature inversions that trap pollutants close to the surface. However, the formation of secondary aerosols (sulphates, nitrates, organics) in these cold and dark conditions and the role of the Arctic boundary layer are still poorly understood. To address this issue, an intensive international measurement campaign, called ALPACA (ALaskan Pollution And Chemical Analysis), will be conducted in January/February 2021 in and around Fairbanks, Alaska. Among the various atmospheric chemical and physical measurements, gas and particles collections will be carried out for multiple isotopic analyses.
The use of stable isotopes over the past decades has demonstrated its ability to provide information relevant for tracing emission sources, individual chemical processes and budgets of atmospheric trace gases. Of particular interest is the propagation of the ozone distinctive oxygen-17 anomaly (Δ17O) into the reactive nitrogen cycle which has led to a better understanding of nitrate formation pathways in various environments. However, there remain some difficulties to interpret the isotopic composition of the nitrate, mainly due to the lack of clearly established understanding about the link between the oxygen and nitrogen isotopic composition of the nitrogen oxides (NOx = NO + NO2), the precursors of nitrate in the atmosphere, and the chemical state of the atmosphere.
In order to interpret more quantitatively the fate of reactive nitrogen using isotopic records, we have developed an effective active method to trap atmospheric NO2 on denuder tubes and have measured, for the first time, its multi-isotopic composition (δ15N, δ18O, and Δ17O). The δ15N values of NO2 trapped at our site in Grenoble, France, show little variability (-11.8 to -4.9 ‰) with negligible N isotopefractionations during the NO and NO2 interconversion due to high NO2/NOx ratios. The main sources of NOx emissions are estimated using a stable isotope model applied to our δ15N measurements; the results indicate the predominance of traffic NOx emissions in this area. The Δ17O values exhibit an important diurnal cycle with a late morning peak at (39.2 ± 1.7) ‰ and a night-time decrease with a late-night minimum at (20.5 ± 1.7) ‰. On top of this general diurnal cycle, Δ17O also shows substantial variability during the day (from 29.7 to 39.2 ‰), certainly driven by changes in the O3 to peroxyl radicals ratio. The night-time decay of Δ17O(NO2) appears to be driven by slow removal of NO2, mostly from its conversion into N2O5, and its formation from the reaction between O3 and emitted NO. As expected, our Δ17O(NO2) values measured towards the end of the night are quantitatively consistent with typical values of Δ17O(O3).
These preliminary results are very promising for the use of Δ17O of NO2 as a probe of the atmospheric oxidative activity and for the interpretation of NO3- isotopic composition records. In the future, samplings and multi-isotopic analysis of atmospheric nitrate performed in parallel with those of NO2 will be of great interest for the study of the full reactive nitrogen cycle.
How to cite: Albertin, S., Bekki, S., and Savarino, J.: Nitrogen isotopes (δ15N) and oxygen isotope anomalies (Δ17O, δ18O) in atmospheric nitrogen dioxide : a new perspective for isotopic constraints on oxidation and aerosols formation processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2634, https://doi.org/10.5194/egusphere-egu21-2634, 2021.
Biogenic gases carbon dioxide, methane and nitrous oxide are regularly analysed in many environments to understand elemental cycling and processes through the ecosphere. They are also of interest to atmospheric chemists for their role in climate change. The Isoprime Tracegas has been key to a large amount of studies providing data on the isotopes of these key dynamic molecules. We shall review some of the notable publications and modifications in the field of atmospheric gas monitoring.
The development of the isoprime precisION mass spectrometer has permitted a new generation of control and automation of the mass spectrometer and integrated peripherals. This has greatly improved the accessibility and versatility of the instruments as a whole.
Taking advantage of the inherent benefits of the isoprime precisION the iso FLOW GHG has been developed for high performance analysis of CO2, N2O and CH4 and has the capacity to be rapidly customised for specific needs with options for N2 and N2O, Hydrogen isotopes in CH4 and denitrifier analysis.
How to cite: Barker, S., Hackett, P., Price, W., and Rosenthal, K.: Analysis and Monitoring atmospheric gases in a high performing and versatile isotope ratio instrument, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15608, https://doi.org/10.5194/egusphere-egu21-15608, 2021.
The stable HCNOS isotope compositions can be reported in various ways depending on scientific domain and needs. The most common notations are 1) the isotope ratio of two stable isotopes; 2) isotope delta value, and 3) atom fraction of one or more of the isotopes. Frequently recalculations between these notations are required for certain applications, particularly when merging different data sets. All these recalculations require using the absolute isotope ratio for the zero points of the stable isotope delta scales (Rstd). However, several Rstd with very contrasting values have been proposed over time and there is no common agreement on which values should be used word-wide (Skrzypek and Dunn, 2020a).
Differences in the selection of Rstdvalue may lead to significant differences between different data sets recalculated from delta value to other notations. These differences in Rstd have a significant influence also on the normalization of raw values but only when the normalization is conducted versus the working standard gas value. We proposed a user-friendly EasyIsoCalculator (http://easyisocalculator.gskrzypek.com) that allows recalculation between the main expressions of isotope compositions using various Rstd and aids for identification of potential inconsistencies in recalculations (Skrzypek and Dunn, 2020b).
Skrzypek G., Dunn P. 2020a. Absolute isotope ratios defining isotope scales used in isotope ratio mass spectrometers and optical isotope instruments. Rapid Communications in Mass Spectrometry 34: e8890.
Skrzypek G., Dunn P., 2020b. The recalculation of the stable isotope expressions for HCNOS – EasyIsoCalculator. Rapid Communications in Mass Spectrometry 34: e8892.
How to cite: Skrzypek, G. and Dunn, P.: Recalculations between different expressions of stable HCNOS isotope results – is it easy?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9774, https://doi.org/10.5194/egusphere-egu21-9774, 2021.
Carbonyl sulfide (COS) is the most abundant sulfur-containing trace gas in the atmosphere, with an average mixing ratio of 500 parts per trillion (ppt). It has a relatively long lifetime of about 2 years, which permits it to travel into the stratosphere. There, it likely plays an important role in the formation of stratospheric sulfur aerosols (SSA), which have a cooling effect on the Earth’s climate. Furthermore, during photosynthetic uptake by plants, COS follows essentially the same pathway as CO2, and therefore COS could be used to estimate gross primary production (GPP). Unfortunately, significant uncertainties still exist in the sources, sinks and global cycling of COS, which need to be overcome. Isotopic measurements of COS could be a promising tool for constraining the COS budget, as well as for investigating its role in the formation of stratospheric sulfur aerosols.
Within the framework of the COS-OCS project, we developed a new measurement system at Utrecht University, that can measure d33S and d34S from COS from small air samples of 2 to 5 L. The aim of the project is to perform a global-scale characterization of COS isotopes by measuring seasonal, latitudinal and altitudinal variations in the troposphere and stratosphere. We will present the newest results from a series of semi-continuous outside air measurements in the Netherlands during the fall and early winter of 2020/2021. The measurement results are interpreted with the help of backward trajectory analyses to characterize the influence of different wind directions and air origins on the COS concentration and isotopic composition.
How to cite: Baartman, S. L., Popa, M. E., Krol, M., and Röckmann, T.: Isotopic Measurements of Carbonyl Sulfide: The First Results from Semi-continuous Outside Air Measurements in the Netherlands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8656, https://doi.org/10.5194/egusphere-egu21-8656, 2021.
Carbonyl sulfide (OCS), the most abundant sulfur-containing gas in the ambient atmosphere, possesses great potential for tracer of the carbon cycle. Sulfur isotopic composition (34S/32S ratio, δ34S) on OCS is a feasible tool to evaluate the OCS budget. We applied the sulfur isotope measurement for the tropospheric OCS cycle and distinguished OCS sources from oceanic and anthropogenic emissions.
Here, we present a developed measurement system of δ34S of OCS and the result of latitudinal (north-south) observations of OCS within Japan using the method. The OCS sampling system was carried to three sampling sites in Japan: Miyakojima (24°8’N, 125°3’E), Yokohama (35°5’N, 139°5’E), and Otaru (43°1’N, 141°2’E). The observed δ34Sof OCS ranging from 9.7 to 14.5‰ reflects the tropospheric OCS cycle. Particularly in winter, latitudinal decreases in δ34Svalues were found to be correlated with increases in OCS concentrations, resulting in an intercept of (4.7 ± 0.8)‰ in the Keeling plot approach. This trend suggests the transport of anthropogenic OCS emissions from the Asian continent to the western Pacific by the Asian monsoon outflow.
The estimated background δ34S of OCS in eastern Asia is consistent with the δ34S of OCS previously reported in Israel and the Canary Islands, suggesting that the background δ34S of OCS in the Northern Hemisphere ranges from 12.0 to 13.5‰. Our constructed sulfur isotopic mass balance of OCS revealed that anthropogenic sources, not merely oceanic sources, account for much of the missing source of atmospheric OCS. This sulfur isotopic constraint on atmospheric OCS is an important step together with isotopic characterizations and analysis using a chemical transport model, will enable detailed quantitative OCS budget and estimation of gross primary production.
How to cite: Kamezaki, K., Hattori, S., and Yoshida, N.: Isotopic constraints on the tropospheric carbonyl sulfide budget, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2214, https://doi.org/10.5194/egusphere-egu21-2214, 2021.
Carbonyl sulfide (COS) is the most abundant reduced sulfur gas in the atmosphere and is used as a tracer for gross primary production (GPP) of terrestrial ecosystems and stomatal conductance of leaves. At present, its usefulness is limited by the uncertainties in the estimation of its sources and sinks. In this study, we aim to understand the COS budget using atmospheric COS enhancements at the Lutjewad tower (53°24’N, 6°21’E, 1m a.s.l.) and atmospheric measurements of COS in the province of Groningen using a mobile van. We infer the sources and sinks of COS using continuous in situ mole fraction profile measurements of COS at Lutjewad. We determined the nighttime COS fluxes to be -3.0 ± 2.6 pmol m-2 s-1 using the radon-tracer correlation approach. We observed enhancements of COS mole fractions on the order of 100 ppt (lasting a few days) to 1000 ppt (lasting a few hours) at three occasions. To quantify potentially unidentified COS sources, we have made additional measurements by collecting air flasks that were analyzed later in the laboratory and with a continuous quantum cascade laser spectrometer. We have identified multiple COS sources, such as biodigesters, sugar production facilities and silicon carbide production facilities. Furthermore, we simulate the Lutjewad COS mole fractions in a Lagrangian model framework to quantitatively understand the COS sources and sinks. These results are useful for improving our understanding of the sources and sinks of COS, contributing to the use of COS as a tracer for GPP.
How to cite: Zanchetta, A., Kooijmans, L. M. J., van Heuven, S., Scifo, A., Scheeren, B., Mammarella, I., Karstens, U., Meijer, H. A. J., Krol, M., and Chen, H.: Identification and quantification of sources and sinks of carbonyl sulfide, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12395, https://doi.org/10.5194/egusphere-egu21-12395, 2021.
The atmospheric trace gas ‘Carbonyl Sulfide (COS)’ has been identified as a possible tracer to estimate global Gross Primary Production (GPP). This is because COS is taken up similarly to CO2 uptake through plant stomata and has almost no respiration. In addition to vegetation activity, COS is removed by soil and chemical reaction in the atmosphere. It enters the atmosphere by emission from oceans and anthropogenic sources (e.g., rayon production). Plants play an important role in the seasonal COS drawdown, but the models that simulate COS biosphere exchange have considerable uncertainty due to lack of observation. The uncertainty is mainly related to the poorly defined ambient COS mixing ratio and enzyme activity, processes that control COS uptake. The ambient COS molecules diffuse into stomatal pores and mesophyll cells, where the molecules are hydrolyzed by the enzyme Carbonic Anhydrase (CA). Due to the lack of understanding of CA activity, previous studies scaled the COS mesophyll uptake with the maximum Rubisco deposition velocity (Vmax), relevant for photosynthesis, and only used the associated temperature response.
This study will improve the estimation of COS vegetation uptake in the Simple Biosphere model version 4 (SiB4), corresponding to different COS mixing ratios from an atmospheric inversion and various environmental conditions. COS flux observations from Europe and North America will be applied. We aim to identify and present: (i) the response of the COS uptake to varying COS mixing ratios and environmental conditions (temperature, humidity, and light), (ii) application of the relationships derived by (i) to the estimation of global COS uptake by the SiB4 model, (iii) investigate the implications for SiB4 calculation of CO2 photosynthesis by the SiB4 model. Unlike the original SiB4 model, where CA uptake is proportional to Vmax and the temperature response identical for all plant types and environments, we will show the nonlinear CA responses to COS mixing ratio, temperature, humidity and light.
How to cite: Cho, A., Kooijmans, L., and Krol, M.: Improved estimation of global vegetation uptake of carbonyl sulfide (COS) in a biosphere model (SiB4) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12944, https://doi.org/10.5194/egusphere-egu21-12944, 2021.
The uptake of carbonyl sulfide (COS) in plants is strongly dependent on stomatal conductance. The COS uptake is therefore strongly related to the photosynthetic uptake of CO2 in plants. As there is a gap in the COS budget with a source missing (or an overestimated sink) in tropical regions, this asks for evaluation of all sources and sinks of COS to be able to apply COS as a photosynthetic tracer. The COS uptake by vegetation and soil is simulated by the Simple Biosphere Model (SiB4) but it has not been validated against ecosystem and vegetation fluxes across different biomes. We evaluated the SiB4 COS biosphere flux with observations and updated it with the latest insights, with the aim to get the best possible estimate of the global COS biosphere sink. Overall, we find good agreement of simulated diurnal and seasonal cycles of COS ecosystem fluxes with flux observations made over grasslands, evergreen needleleaf forest and deciduous broadleaf forests over Europe and Northern America. We improved the simulations of COS soil exchange with the implementation of the Ogee et al. (2016) soil model such that SiB4 is now capable of simulating COS emissions from soils. We found that accounting for varying COS mixing ratios (retrieved from an inversion by the TM5-4DVAR model) plays a large role in determining the global COS biosphere sink. With these modifications to the model, we find an average underestimation of the COS biosphere flux of 11 % compared to observations. Furthermore, our model modifications caused a drop in the global COS biosphere sink from 967 Gg S yr-1 in the original model to 788 Gg S yr-1 in the updated version. The largest drop in fluxes is over the tropical regions, mostly driven by lower COS mixing ratios and contributes towards closing the gap in the COS budget. However, given the underestimation of COS uptake in the boreal and temperature regions, it is unlikely that the remaining gap in the COS budget is caused by an overestimated tropical biosphere sink.
How to cite: Kooijmans, L., Cho, A., Ma, J., Baker, I., Kaushik, A., and Krol, M.: Validation and development of carbonyl sulfide biosphere exchange in the Simple Biosphere Model (SiB4), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8794, https://doi.org/10.5194/egusphere-egu21-8794, 2021.
17O-excess (Δ17O = δ17O − 0.52 × δ18O) of sulfate trapped in Antarctic ice cores has been proposed as a potential tool for assessing past oxidant chemistry, while insufficient understanding of atmospheric sulfate formation around Antarctica hampers its interpretation. To probe influences of regional specific chemistry, we compared year-round observations of Δ17O of non-sea-salt sulfate in aerosols (Δ17O(SO42−)nss) at Dome C and Dumont d’Urville, inland and coastal sites in East Antarctica, throughout the year 2011. Although Δ17O(SO42–)nss at both sites showed consistent seasonality with summer minima (~1.0 ‰) and winter maxima (~2.5 ‰) owing to sunlight-driven changes in the relative importance of O3-oxidation to OH- and H2O2-oxidation, significant inter-site differences were observed in austral spring–summer and autumn. The co-occurrence of higher Δ17O(SO42–)nss at inland (2.0 ± 0.1 ‰) than the coastal site (1.2 ± 0.1 ‰) and chemical destruction of methanesulfonate (MS–) in aerosols at inland during spring–summer (October to December), combined with the first estimated Δ17O(MS–) of ~16 ‰, implies that MS– destruction produces sulfate with high Δ17O(SO42–)nss of ~12 ‰. If contributing to the known post-depositional decrease of MS– in snow, this process should also cause a significant post-depositional increase in Δ17O(SO42–)nss over 1 ‰, that can reconcile the discrepancy between Δ17O(SO42–)nss in the atmosphere and ice.
How to cite: Ishino, S., Hattori, S., Legrand, M., Chen, Q., Alexander, B., Shao, J., Huang, J., Jaegle, L., Jourdain, B., Preunkert, S., Yamada, A., Yoshida, N., and Joel, S.: Regional characteristics of atmospheric sulfate formation in East Antarctica imprinted on 17O-excess signature, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2527, https://doi.org/10.5194/egusphere-egu21-2527, 2021.
Oxygen-17 anomaly (Δ17O) has been used as a probe to constrain the relative importance of different pathways leading to sulfate formation. Here, we report the Δ17O values in atmospheric sulfate collected at a remote site in the Mt. Everest region to decipher the possible formation mechanisms of sulfate in such a pristine environment. The Δ17O in non-dust sulfate show higher values than most existing data in modern atmospheric sulfate. The seasonality of Δ17O in non-dust sulfate exhibits high values in the pre-monsoon and low values in the monsoon, opposite to the seasonality in Δ17O for both sulfate and nitrate (i.e., minima in warm season and maxima in cold season) observed from diverse geographic sites. This high Δ17O in non-dust sulfate found in this region clearly indicates the important role of the S(IV) + O3 pathway in atmospheric sulfate formation promoted by high cloud water pH conditions. In turn, this study highlights observational evidence that atmospheric acidity plays an important role in controlling sulfate formation pathways particularly for dust-rich environments.
How to cite: Hattori, S., Wang, K., Lin, M., Ishino, S., Alexander, B., Kamezaki, K., Yoshida, N., and Kang, S.: Isotopic evidence for importance of atmospheric acidity on sulfate formation in the Mt. Everest region, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3649, https://doi.org/10.5194/egusphere-egu21-3649, 2021.
Anthropogenic and biogenic activities, along with the fluxes of sea salt, volcanic, wildfire and oceanic sulfate-reducing microorganisms (SRM), contribute significantly to the atmospheric sulfur budget.(1,2)
There is still uncertainty and debate between studies about the magnitude of the importance of oceanic hydrogen sulfide (H2S) produced by SRM, as well as its ability to diffuse to the upper water column and its contribution to the atmospheric sulfur budget. While some studies believe that the majority of H2S is re-oxidized and is less likely to reach the atmosphere (3,4), there is evidence of the existence of H2S in the upper water columns and even in the atmosphere (2,5). H2S produced by SRM, emitted to the atmosphere, along with the anthropogenic sulfur dioxide (SO2) and dimethyl sulfide (DMS), undergo atmospheric oxidation processes. Sulfate (SO42-), as one of the main oxidized products, may nucleate with water vapor, ammonia and organic oxides (6,7), and subsequently grow to bigger particle sizes. These particles affect the climate directly and indirectly and change the radiation balance of the Earth-atmosphere system. (8,9,10)
This study assessed the seasonal trends of major atmospheric sulfur species including SO2, sulfate, and biogenic and anthropogenic sulfate of gas, aerosol and precipitation samples, collected by Canadian Air and Precipitation Monitoring Network (CAPMoN), Environment of Canada, at Saturna Island, B.C, between 1998-2010. We then explored the oceanic phytoplankton activities and DMS production, based on sulfur isotope composition and found the importance of DMS contribution to the summertime atmospheric sulfur budget. A handful of samples (~10-30%) displayed negative sulfur isotope compositions, outside the range of anthropogenic and biogenic isotope values. Potential factors that could produce such negative sulfur isotope composition values include isotopic fractionation, fluxes from mineral dust events, volcanic eruptions, wildfires and microbial sulfate reduction (MSR). Our study found that MSR was the only feasible explanation for these very negative sulfur isotope compositions in non-sea salt sulfate samples. H2S in our study was a 4th potential contributor to the atmospheric sulfur budget, along with the 3 major sources of anthropogenic, biogenic DMS, and sea-salt sulfate, in this long-term atmospheric sulfur study.
How to cite: mostafaei, M., Norman, A.-L., and Mohamed, F.: Exploring the atmospheric sulfur trends and the potential contribution of sulfate-reducing microorganism activities to the atmospheric sulfur budget at Saturna Island, B.C, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10534, https://doi.org/10.5194/egusphere-egu21-10534, 2021.
We present long-term results of δ13C-CO2, δ18O-CO2, δ17O-CO2 and “excess” 17O-CO2 or Δ17O-CO2 measurements in whole air flask samples collected at Lutjewad monitoring station in the Netherlands using an Aerodyne Quantum Cascade Dual-Laser Spectrometer system (QCDLAS). The station is located at the Dutch Wadden sea coast (6.353°E, 53.404°N) in a rural environment. The flask samples have been collected at 60 m altitude at a bi-weekly rate, spanning from July 2016 until the end of 2020. The location of Lutjewad station allows to measure clean marine background air from the north-northwest (~15% of the time) in contrast to continental air from a prevalent south-westerly direction (~50% of the time). Our observations include the summers of 2018 and 2019 which saw exceptionally hot and dry conditions in large parts of Europe, including the Netherlands.
The Δ17O-CO2 anomaly is defined as the deviation from normal mass dependent fractionation reflected in CO2 equilibrated with water, occurring over water bodies, but mainly in plant leaves. Atmospheric Δ17O-CO2 has been used as a parameter to study gross primary production (GPP), notably as a function of water availability. Here, the determination of Δ17O-CO2 is derived from the direct measurement of δ17O-CO2 next to δ18O-CO2 (Δ17O = ln(δ17O +1)-0.5229×ln(δ18O +1)). Using the summer 2018 and 2019 results we investigate the potential of using the Δ17O-CO2 signal derived from QCDLAS measurements from Lutjewad as a tracer for suppressed plant assimilation due to water stress.
How to cite: Steur, F., Scheeren, B., Peters, W., and Meijer, H.: Long-term observations of δ13C-CO2, δ18O-CO2, δ17O-CO2 and “excess” 17O-CO2 by Quantum Cascade Dual-Laser Absorption Spectrometry in whole air flask samples from Lutjewad station, the Netherlands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15139, https://doi.org/10.5194/egusphere-egu21-15139, 2021.
Mid-infrared optical absorption spectroscopy techniques, in particular with quantum cascade lasers (QCLs), allow realization of highly sensitive and compact spectrometers for the detection of greenhouse gases such as carbon dioxide and its stable isotopes . Clumped isotope analysis of carbon dioxide is evolving into an established method in environmental, geological, and biogeochemical research. Optical clumped isotope thermometry was recently demonstrated for the 13C16O18O isotopologue . Measurements of all isotopologues involved in isotope exchange reaction 12C16O2 + 12C18O2 ⇌ 212C16O18O can provide an independent temperature estimate to conventional Δ47 or Δ638 thermometry. The added dimension can resolve kinetic effects and verify temperature measurements. However, applications of clumped isotopes using ultra-high resolution mass spectrometry are strongly limited by the sample amount, long measurement times, and isobaric interferences .
In this work, we present an alternative approach based on laser spectroscopy for the simultaneous measurement of 12C18O2, 12C16O2, and 12C16O18O. The main experimental challenge to optically measure 12C18O2 (natural abundance 3.95×10-6) is the large spectral interference caused by the hot band transitions of the most abundant 12C16O2 isotopologue. Our strategy to overcome this limitation is to analyze the sample CO2 gas at low temperature, i.e. close to its sublimation point. This reduces the population of these hot band transitions, thereby reducing their linestrength by a factor of 105.
The spectrometer deploys a thermoelectrically cooled, distributed feedback (DFB) QCL emitting at 2305 cm-1. We operate the laser in intermittent continuous wave (iCW) mode  with a repetition rate of 6.5 kHz. The laser beam is coupled into a compact segmented circular multipass cell (SC-MPC)  with an optical path length of 6 m. The cell is enclosed in a high vacuum chamber and is stabilized at 150 K with a low-vibration Stirling- cooler.
Using pure CO2 gas samples at 10 mbar pressure, we demonstrate a precision of 0.03 ‰ and 0.02 ‰ in 12C18O2/12C16O2 and 12C16O18O/12C16O2 ratios in less than one minute averaging time. Repeated series of 30 consecutive measurements of Δ48 has a standard deviation of 0.12 ‰ (SE = 0.022 ‰). The isotope ratio scale is investigated through the analysis of pure CO2 samples, which range in δ18O from -25 ‰ to -14 ‰ vs VSMOW . The instrument reproduced the scale within 0.2 ‰, which corresponds to the uncertainty of the reported δ18O values.
This unique approach of using cryogenically cooled MPC to reduce the interference of hot band transition from abundant isotopes, represents a promising method for high-precision quantification of the CO2 clumped isotopes, opening up new possibilities in geosciences.
 P. Sturm et al, Atmospheric Measurement Techniques, 6(7), 1659, 2013
 I. Prokhorov et al, Sci Rep, 9(1), p. 4765, 2019
 D. Bajnai et al., Nature Communications, 11(1), pg 4005, 2020
 M. Fischer et al Opt. Express, 22(6), 7014, 2014
 M. Graf et al, Optics Letters, 43(11) 2434 2018
How to cite: Nataraj, A., Gianella, M., Prokhorov, I., Tuzson, B., Faist, J., and Emmenegger, L.: Quantum Cascade Laser absorption spectroscopy of clumped 12C18O2, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12407, https://doi.org/10.5194/egusphere-egu21-12407, 2021.
Constant increasing of atmospheric carbon dioxide (CO2) concentration has raised many concerns over the past 60 years due to its climate regulating effect. The ubiquitous increasing trends have been observed across the globe and it is believed to be a consequence of anthropogenic combustions of fossil fuels and land use change. For the anthropogenically emitted CO2, roughly 15% is fixed by the biosphere. Precise quantification of these two important carbon fluxes would provide us a better understanding of global carbon cycle as well as predicting future climate change. In this study, we used the CO2 and the δ13C/Δ14C values measured at three different locations: Mauna Loa, Niwot Ridge and the South Pole, to explore the relative contributions of biosphere carbon sink, and the anthropogenic carbon sources to the atmosphere. Δ14C signatures showed that anthropogenically combusted fossil fuels are the primary source for the increasing atmospheric CO2 concentrations, and about a 3‰ decrease in atmospheric Δ14C equals to approximate 1.1 ppm of fossil fuel CO2 added to the atmosphere. The CO2-enhanced carbon storage (CO2-ECS) by the global biosphere was also calculated and we concluded that the biosphere is absorbing about an addition of at least 0.6 Pg CO2 yr-1 due to the CO2 enrichment.
How to cite: Wang, Y.: δ13C/Δ14C compositions of atmospheric CO2 and its applications in the quantifications of biosphere sink and anthropogenic source, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-265, https://doi.org/10.5194/egusphere-egu21-265, 2021.
Carbon dioxide (CO2) is an important greenhouse gas, and it accounts for about 20% of the present-day anthropogenic greenhouse effect. Atmospheric CO2 is cycled between the terrestrial biosphere and the atmosphere through various land-surface processes and thus links the atmosphere and terrestrial biosphere through positive and negative feedback. Since multiple trace gas elements are linked by common biogeochemical processes, multi-species analysis is useful for reinforcing our understanding and can help in partitioning CO2 fluxes. For example, in the northern hemisphere, CO2 has a distinct seasonal cycle mainly regulated by plant photosynthesis and respiration and it has a distinct negative correlation with the seasonal cycle of the δ13C isotope of CO2, due to a stronger isotopic fractionation associated with terrestrial photosynthesis. Therefore, multi-species flask-data measurements are useful for the long-term analysis of various green-house gases. Here we try to infer the complex interaction between the atmosphere and the terrestrial biosphere by multi-species analysis using atmospheric flask measurement data from different NOAA flask measurement sites across the northern hemisphere.
This study focuses on the long-term changes in the seasonal cycle of CO2 over the northern hemisphere and tries to attribute the observed changes to driving land-surface processes through a combined analysis of the δ13C seasonal cycle. For this we generate metrics of different parameters of the CO2 and δ13C seasonal cycle like the seasonal cycle amplitude given by the peak-to-peak difference of the cycle (indicative of the amount of CO2 taken up by terrestrial uptake), the intensity of plant productivity inferred from the slope of the seasonal cycle during the growing season , length of growing season and the start of the growing season. We analyze the inter-relation between these metrics and how they change across latitude and over time. We hypothesize that the CO2 seasonal cycle amplitude is controlled both by the intensity of plant productivity and period of the active growing season and that the timing of the growing season can affect the intensity of plant productivity. We then quantify these relationships, including their variation over time and latitudes and describe the effects of an earlier start of the growing season on the intensity of plant productivity and the CO2 uptake by plants.
How to cite: Kariyathan, T., Peters, W., Marshall, J., Bastos, A., and Reichstein, M.: The use of multi-tracer flask-measurements to understand changes in the land-surface processes., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15179, https://doi.org/10.5194/egusphere-egu21-15179, 2021.
In-depth knowledge about carbon (C) flows within trees and from the trees to forest ecosystem via respiration is essential for accurate modeling of tree growth and C balance. However, significant gaps still exist in our understanding about how trees allocate C for growth and respiration of different tree organs, which makes it difficult to predict the response of forest growth to climate change. A powerful tool to study C allocation within trees is stable C isotope ratio (the ratio of 13C to 12C relative to a reference, noted as δ13C), as this signal is passed from C sources to C sinks with isotopic fractionation along the pathway. In this study, we monitored the δ13C signal of CO2 fluxes of shoot (Acanopy), stem (Rstem) and soil (Rsoil) in a Scots pine (Pinus sylvestris L.) dominated boreal forest in southern Finland for summer 2018, which included a month-long dry period. We also traced the growth of current-year shoots, needles, stem, and fine roots (fibrous and pioneer roots) and the concentrations and δ13C of putative substrates (sugars and starch) in phloem and roots of Scots pine over the growing season. We calculated the correlations between substrate concentrations and respiration fluxes, as well as the correlations between δ13C of Acanopy and δ13C of Rsoil or δ13C of Rstem with varying time lags from 3 d to 14 d for different tree organ growth periods and the dry period. We found tight couplings between photosynthesis and respiration, when newly assimilated sugars were allocated to stem or roots for growth or for drought response. These couplings include: 1) a synchrony between fibrous root growth and the concentrations of bulk sugars and starch in roots, associated with increases in Rsoil under high root substrate concentrations; 2) promoted nighttime Rstem under high substrate supply to stem, which is seen as increased phloem glucose to sucrose ratio; 3) shorter time lags between δ13C of Acanopy and δ13C of Rstem under higher stem growth demands; 4) shorter time lags between δ13C of Acanopy and δ13C of Rsoil under drought stress than with no water stress. The time lags between δ13C of Acanopy and δ13C of Rsoil or δ13C of Rstem being not uniform further implies that tree C allocation patterns are dynamic over the growing season. In addition, the C allocation to stem and roots occurred after full expansion of current-year shoots or needles, reflecting a whole tree C allocation strategy for growth demands of different tree organs, which prioritizes the demands of source organs. We suggest that the dynamics of C allocation in response to tree organ growth and drought stress should be considered in whole tree C allocation models for projecting forest growth under climate change.
How to cite: Tang, Y., Schiestl-Aalto, P., Ryhti, K., Kulmala, L., Sahlstedt, E., Saurer, M., Jyske, T., Kolari, P., Bäck, J., and Rinne-Garmston, K.: Tree growth and drought impact the dynamics of C allocation and change the coupling between photosynthesis and respiration in stem and soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11938, https://doi.org/10.5194/egusphere-egu21-11938, 2021.
The stable isotopic compositions of carbon and oxygen in terrestrial plants can provide valuable insights into plant eco-physiological responses to environmental changes at seasonal to annual resolution. Yet, the potential of these datasets to study land-atmosphere interactions remains under-exploited. Here, we present some examples of how stable carbon isotopes (δ13C) measured in plant materials (leaves and tree-rings) can be used to explore changes in the magnitude and variability of carbon and water flux exchanges between the vegetation and the atmosphere and to improve land surface models.
First, we show that the discrimination against 13C (Δ13C), calculated as the difference in δ13C between the source atmospheric CO2 and the plant material studied, varies strongly between regions and biomes and is useful for better understanding the CO2 fertilisation effect of plant growth. For example, tree-ring Δ13C records from boreal evergreen forests in North America increased linearly with rising CO2 during the 20th century, suggesting that those forests have actively contributed to the land carbon sink by removing CO2 from the atmosphere at a relatively constant rate. However, such an increase in Δ13C with rising CO2 is not observed everywhere. We found that over the same time period, while some forests had a fairly constant Δ13C, others exhibited a slight decrease in Δ13C over time, which might indicate a reduction of the capacity of trees to absorb CO2. Using a response function approach, we show that the differences between sites and regions are most likely the result of different evaporative demands and soil water availability conditions experienced by forests.
We then discuss how predictions of the coupled carbon and water cycles by vegetation models can be improved by incorporating stable carbon isotopes to constrain the model representation of carbon-water fluxes regulation by leaf stomata. Specifically, we examine and evaluate simulations from the JULES vegetation model at different eddy-covariance forest sites where stable carbon isotopic data and canopy flux measurements are available. Overall, our analyses have strong implications for the understanding of historical changes in the strength of the CO2 fertilisation effect and in the water use efficiency of terrestrial ecosystems across regions.
How to cite: Lavergne, A., Andreu-Hayles, L., Belmecheri, S., Guerrieri, R., and Graven, H.: Stable carbon isotopes as powerful tools for studying land-atmosphere flux exchanges and improving land surface models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11232, https://doi.org/10.5194/egusphere-egu21-11232, 2021.
Stable isotopes can diagnose the response of plants to changing climate as the performance of trees in past climatic conditions is archived in the stable carbon and oxygen isotope composition (δ13C and δ18O, respectively) of tree rings. To take advantage of these records, understanding the formation of isotopic signals in newly assimilated photosynthates is necessary. Despite a voluminous literature, there exists a gap between the model- and data-oriented studies, which if welded together would benefit this line of inquiry. A unique dataset covering two growing seasons in a boreal Scots pine stand situated in Southern Finland (61.9°N, 24.3°E) is employed and is accompanied with mechanistic modeling driven by environmental conditions. Data includes: (i) shoot gas exchange of vapor, CO2 and its δ13C composition, (ii) δ13C in needle bulk sugar and sucrose alone, (iii) δ18O in water in precipitation, soil, twigs and needles, and (iv) δ18O in needle bulk sugar. Overall, observed exchange rates and isotopic composition of fluxes as well as in water and sugar pools were well reproduced using the model. We further address challenges common to the analysis of isotopic signals. Firstly, time scales and integration over them is an unavoidable challenge of data sampled at different intervals, representing either snapshots or a longer history of processes. As an example of this, we illustrate that δ18O in needle water reacts instantaneously to environmental conditions, while the δ18O signal in needle sugars is an integration over time, and thus relating the latter to instantaneous environmental conditions is less evident. Given that tree-ring studies are more and more focused on intra-annual variation in δ13C and δ18O, integration over time scales cannot be neglected. Second, using model sensitivity analysis, we showcase the relative importance of environmental drivers on the variation in δ13C and δ18O – the typical aim of empirical research and paleoclimatological reconstruction. It is commonly acknowledged that the main environmental driver of δ13C or δ18O variation can differ between sites and time periods. At the study site here, the variation in δ18O seems solely driven by relative humidity, but we can, for instance, show that this would change if the δ18O signal of source water varied considerably. We are of the opinion that illustrating such points with a model-data fusion approach is a necessary (but not sufficient) first step to bridge the gap between modeling and empirical approaches, and fostering further interpretation of isotopic signals in trees.
How to cite: Leppä, K., Schiestl-Aalto, P., Tang, Y., Sahlstedt, E., Kolari, P., Launiainen, S., Katul, G., Saurer, M., and Rinne-Garmston, K.: Model-data fusion depicting the key processes and environmental drivers of photosynthates δ13C and δ18O compositions in boreal Scots Pine, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7088, https://doi.org/10.5194/egusphere-egu21-7088, 2021.
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