BG2.2

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.

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.

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.

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. [1] (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 [2] (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.

References:

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.

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.

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(SO₄^2–)_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(SO₄^2–)_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(SO₄^2–)_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(SO₄^2–)_nss over 1 ‰, that can reconcile the discrepancy between Δ¹⁷O(SO₄^2–)_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 (SO₄^2-), 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 4^th 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 [1]. 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 [2]. 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 [3].

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 [4] with a repetition rate of 6.5 kHz. The laser beam is coupled into a compact segmented circular multipass cell (SC-MPC) [5] 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.

[1] P. Sturm et al, Atmospheric Measurement Techniques, 6(7), 1659, 2013

[2] I. Prokhorov et al, Sci Rep, 9(1), p. 4765, 2019

[3] D. Bajnai et al., Nature Communications, 11(1), pg 4005, 2020

[4] M. Fischer et al  Opt. Express, 22(6), 7014, 2014

[5] 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.

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.