Interannual variations in the Δ(17O) signature of atmospheric CO2 at two mid-latitude sites suggest a close link to stratosphere-troposphere exchange

Δ(17O )measurements of atmospheric CO2 have the potential to be a tracer for gross primary production and stratosphere-troposphere mixing. A positive Δ(17O) originates from intrusions of stratospheric CO2, whereas values close to zero result from equilibration of CO2 and water, predominantly happening inside plants. The stratospheric source of CO2 carrying high Δ(17O) is, however, not well defined in the current models. More and long-time atmospheric measurements are needed to improve this. We present records of the Δ(17O) of atmospheric CO2 conducted with laser absorption spectroscopy, from Lutjewad in the Netherlands (53° 24’N, 6° 21’E) and Mace Head in Ireland (53° 20’ N, 9° 54’ W), covering the period 2017–2022. The records are compared with a 3-D model simulation, and we study potential model improvements. Both records show significant interannual variability, of up to 0.3 ‰. The total range covered by smoothed monthly averages from the Lutjewad record is -0.065 to 0.046 ‰, which is significantly higher than the range of -0.009 and 0.036 ‰ of the model simulation. The 100 hPa 60–90° North monthly mean temperature anomaly was used as a proxy to scale stratospheric downwelling in the model. This strongly improves the correlation coefficient of the simulated and observed year-to-year Δ(17O) variations over the period 2019–2021, from 0.37 to 0.81. As the Δ(17O) of atmospheric CO2 seems to be dominated by stratospheric influx, its use a as a tracer for stratosphere-troposphere exchange should be further investigated

Data treatment and corrections for estimating H2O and CO2 isotope fluxes from high-frequency observations

Current understanding of land-Atmosphere exchange fluxes is limited by the fact that available observational techniques mainly quantify net fluxes, which are the sum of generally larger, bidirectional fluxes that partially cancel out. As a consequence, validation of gas exchange fluxes applied in models is challenging due to the lack of ecosystem-scale exchange flux measurements partitioned into soil, plant, and atmospheric components. One promising experimental method to partition measured turbulent fluxes uses the exchange-process-dependent isotopic fractionation of molecules like CO2 and H2O. When applying this method at a field scale, an isotope flux (flux) needs to be measured. Here, we present and discuss observations made during the LIAISE (Land surface Interactions with the Atmosphere over the Iberian Semi-Arid Environment) 2021 field campaign using an eddy covariance (EC) system coupled to two laser spectrometers for high-frequency measurement of the isotopic composition of H2O and CO2. This campaign took place in the summer of 2021 in the irrigated Ebro River basin near Mollerussa, Spain, embedded in a semi-Arid region. We present a systematic procedure to scrutinise and analyse measurements of the-flux variable, which plays a central role in flux partitioning. Our experimental data indicated a larger relative signal loss in the fluxes of H2O compared to the net ecosystem flux of H2O, while this was not true for CO2. Furthermore, we find that mole fractions and isotope ratios measured with the same instrument can be offset in time by more than a minute for the H2O isotopologues due to the isotopic memory effect. We discuss how such artefacts can be detected and how they impact flux partitioning. We argue that these effects are likely due to condensation of water on a cellulose filter in our inlet system. Furthermore, we show that these artefacts can be resolved using physically sound corrections for inlet delays and high-frequency loss. Only after such corrections and verifications are made can ecosystem-scale fluxes be partitioned using isotopic fluxes as constraints, which in turn allows for conceptual land-Atmosphere exchange models to be validated

Global 3-D Simulations of the Triple Oxygen Isotope Signature Δ17O in Atmospheric CO2

The triple oxygen isotope signature Δ¹⁷O in atmospheric CO₂, also known as its “¹⁷O excess,” has been proposed as a tracer for gross primary production (the gross uptake of CO₂ by vegetation through photosynthesis). We present the first global 3-D model simulations for Δ¹⁷O in atmospheric CO₂ together with a detailed model description and sensitivity analyses. In our 3-D model framework we include the stratospheric source of Δ¹⁷O in CO₂ and the surface sinks from vegetation, soils, ocean, biomass burning, and fossil fuel combustion. The effect of oxidation of atmospheric CO on Δ¹⁷O in CO2 is also included in our model. We estimate that the global mean Δ¹⁷O (defined as Δ¹⁷O = ln( ¹⁷O + 1) − RL · ln( ¹⁸O + 1) with RL = 0.5229) of CO₂ in the lowest 500 m of the atmosphere is 39.6 per meg, which is ∼20 per meg lower than estimates from existing box models. We compare our model results with a measured stratospheric Δ¹⁷O in CO₂ profile from Sodankylä (Finland), which shows good agreement. In addition, we compare our model results with tropospheric measurements of Δ¹⁷O in CO₂ from Göttingen (Germany) and Taipei (Taiwan), which shows some agreement but we also find substantial discrepancies that are subsequently discussed. Finally, we show model results for Zotino (Russia), Mauna Loa (United States), Manaus (Brazil), and South Pole, which we propose as possible locations for future measurements of Δ¹⁷O in tropospheric CO₂ that can help to further increase our understanding of the global budget of Δ¹⁷O in atmospheric CO₂

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Gas-phase advanced oxidation as an integrated air pollution control technique

Gas-phase advanced oxidation (GPAO) is an emerging air cleaning technology based on the natural self-cleaning processes that occur in the Earth’s atmosphere. The technology uses ozone, UV-C lamps and water vapor to generate gas-phase hydroxyl radicals that initiate oxidation of a wide range of pollutants. In this study four types of GPAO systems are presented: a laboratory scale prototype, a shipping container prototype, a modular prototype, and commercial scale GPAO installations. The GPAO systems treat volatile organic compounds, reduced sulfur compounds, amines, ozone, nitrogen oxides, particles and odor. While the method covers a wide range of pollutants, effective treatment becomes difficult when temperature is outside the range of 0 to 80 °C, for anoxic gas streams and for pollution loads exceeding ca. 1000 ppm. Air residence time in the system and the rate of reaction of a given pollutant with hydroxyl radicals determine the removal efficiency of GPAO. For gas phase compounds and odors including VOCs (e.g. C6H6 and C3H8) and reduced sulfur compounds (e.g. H2S and CH3SH), removal efficiencies exceed 80%. The method is energy efficient relative to many established technologies and is applicable to pollutants emitted from diverse sources including food processing, foundries, water treatment, biofuel generation, and petrochemical industries

Fractionation of clumped isotopes of CO2 during photosynthesis

Stable isotope (δ13C and δ18O) and mole fraction measurements of CO2 are used to constrain the carbon cycle. However, the gross fluxes of the carbon cycle, especially photosynthesis and respiration, remain uncertain due to the challenging task of distinguishing individual flux terms from each other. The clumped isotope composition (Δ47) of CO2 has been suggested as an additional tracer for gross CO2 fluxes since it depends mainly on temperature but not on the bulk isotopic composition of leaf, soil and surface water, unlike δ18O of CO2. In this study, we quantify the effect of photosynthetic gas exchange on Δ47 of CO2 using leaf cuvette experiments with two C3 and one C4 plants and discuss challenges and possible applications of clumped isotope measurements. The experimental results are supported by calculations with a leaf cuvette model. Our results demonstrate how the effect of gas exchange on Δ47 is controlled by CO2-H2O isotope exchange (using plants with different carbonic anhydrase activity), and kinetic fractionation as CO2 diffuses into and out of the leaf (using plants with different stomatal and mesophyll conductance). We experimentally confirm the previously suggested dependence of Δ47­­ on the stomatal conductance and back-diffusion flux

Isotope flux data of CO2 and H2O measured during the LIAISE 2021 field campaign described in: Moonen et al. 2023 (AMT)

Ecosystem scale isoflux measurements where eddy covariance flux data is available, processed using EddyPro.In addition, isotope flux data is available for CO2 and H2O including d13C, d18O, and dD.Details in:Moonen, R. P. J., Adnew, G. A., Hartogensis, O. K., Vilà-Guerau De Arellano, J., Bonell Fontas, D. J., Röckmann, T., & Moonen, R. (n.d.). Data treatment and corrections for estimating H 2 O and CO 2 isotope fluxes from high-frequency observations. https://doi.org/10.5194/egusphere-2023-785The data composes of a 6 day measurement period during the LIAISE field campaign in the EBRO basain in Spain.Details in:Boone, A., Bellvert, J., Best, M., Brooke, J., Canut-Rocafort, G., Cuxart, J., Hartogensis, O., le Moigne, P., Miró, R., & Polcher, J. (2021). Updates on the International Land Surface Interactions with the Atmosphere over the Iberian Semi-Arid Environment (LIAISE) Field Campaign. https://cw3e.ucsd.eduVariable info for isotope data (13C as example):Fd13C refers to an iso-forcing [permil m-1 s-1]CF_.. refers to a correction factor of the isoforcing, based on eighter OPGA scaling or spectral scaling [-]d13C_source is the source isotopic composition based derived [permil]d13C refers to the atmospheric isotopic composition [permil]...._se refers to the absolute (standard) error or the ... variable.Additional info:crop type = Alfalfameasurement height = 2.45mContact:[email protected]</p

Exploring the diurnal cycle of Δ17O in CO2 at the ecosystem level

The triple oxygen isotope signature Δ17O in atmospheric CO2 is a potential tracer for gross primary production (GPP). However, interpretation of Δ17O in atmospheric CO2 is complicated by the contributions from respired CO2, isotopic exchange with soil and ocean water, and the release of CO2 by fossil fuel combustion and biomass burning. We studied Δ17O in CO2 at the ecosystem level, which is the domain that integrates the contributions from vegetation and soil to the atmospheric signal. We report for the first time the observed diurnal variation of Δ17O in CO2, measured from air samples collected on 15-16 August 2019 at the mid-latitude pine forest Loobos (ICOS L2 ecosystem site). We also measured the isotopic signatures δ13C and δ18O in CO2 close to the surface (at 0.5 m height, inside the canopy) and from the top of the tower (1-2 m above the canopy). To support the interpretation of the measurements, we used a land-atmosphere model that satisfactorily reproduces the diurnal variability of the interaction between leaf/canopy and the convective boundary layer using mixed-layer theory assumptions (CLASS). Also, we used the global atmospheric transport model TM5 to (1) quantify the contribution of different sources that affect Δ17O in CO2 at Loobos; and (2) extend our analysis of the diurnal cycle to the global scale. Our methodology demonstrates the added value of isotope measurements at ICOS ecosystem and tall-tower sites, and how to integrate meteorological and ecological observations from the canopy up to the atmospheric boundary layer. This study contributes to our ongoing effort of creating an overview of different methods for quantifying photosynthesis from a top-down perspective (concentration-based methods and remote sensing) in a review paper for which we are open to other contributions

Exploring the diurnal cycle of Δ17O in CO2 at the ecosystem level

The triple oxygen isotope signature Δ17O in atmospheric CO2 is a potential tracer for gross primary production (GPP). However, interpretation of Δ17O in atmospheric CO2 is complicated by the contributions from respired CO2, isotopic exchange with soil and ocean water, and the release of CO2 by fossil fuel combustion and biomass burning. We studied Δ17O in CO2 at the ecosystem level, which is the domain that integrates the contributions from vegetation and soil to the atmospheric signal. We report for the first time the observed diurnal variation of Δ17O in CO2, measured from air samples collected on 15-16 August 2019 at the mid-latitude pine forest Loobos (ICOS L2 ecosystem site). We also measured the isotopic signatures δ13C and δ18O in CO2 close to the surface (at 0.5 m height, inside the canopy) and from the top of the tower (1-2 m above the canopy). To support the interpretation of the measurements, we used a land-atmosphere model that satisfactorily reproduces the diurnal variability of the interaction between leaf/canopy and the convective boundary layer using mixed-layer theory assumptions (CLASS). Also, we used the global atmospheric transport model TM5 to (1) quantify the contribution of different sources that affect Δ17O in CO2 at Loobos; and (2) extend our analysis of the diurnal cycle to the global scale. Our methodology demonstrates the added value of isotope measurements at ICOS ecosystem and tall-tower sites, and how to integrate meteorological and ecological observations from the canopy up to the atmospheric boundary layer. This study contributes to our ongoing effort of creating an overview of different methods for quantifying photosynthesis from a top-down perspective (concentration-based methods and remote sensing) in a review paper for which we are open to other contributions

Fractionation of clumped isotopes of CO2 during photosynthesis

Stable isotope (δ13C and δ18O) and mole fraction measurements of CO2 are used to constrain the carbon cycle. However, the gross fluxes of the carbon cycle, especially photosynthesis and respiration, remain uncertain due to the challenging task of distinguishing individual flux terms from each other. The clumped isotope composition (Δ47) of CO2 has been suggested as an additional tracer for gross CO2 fluxes since it depends mainly on temperature but not on the bulk isotopic composition of leaf, soil and surface water, unlike δ18O of CO2. In this study, we quantify the effect of photosynthetic gas exchange on Δ47 of CO2 using leaf cuvette experiments with two C3 and one C4 plants and discuss challenges and possible applications of clumped isotope measurements. The experimental results are supported by calculations with a leaf cuvette model. Our results demonstrate how the effect of gas exchange on Δ47 is controlled by CO2-H2O isotope exchange (using plants with different carbonic anhydrase activity), and kinetic fractionation as CO2 diffuses into and out of the leaf (using plants with different stomatal and mesophyll conductance). We experimentally confirm the previously suggested dependence of Δ47­­ on the stomatal conductance and back-diffusion flux