CO2 Budget Research Articles

CO2 flux from the French Massif Central groundwaters: Modelling and quantitative estimation of the degassing process

Passive rift systems are often characterized by CO2 degassing, witnessed by the presence of mineral and thermal springs, bubbling pools, mofetes. Despite these field manifestations, the quantitative estimation of the CO2 budget released to the atmosphere from these geodynamic structures is not well constrained. Here, we examine the chemistry of 169 springs, the isotopic composition of the dissolved carbon (δ13CTDIC) of 33 springs and the dissolved gases composition of 6 springs from the French Massif Central, part of the European Cenozoic Rift System (ECRIS), in order to describe the CO2 degassing process and to compute the CO2 emission rate released from groundwaters at regional scale. Water-gas-rock models reveal that the separation of gas from the liquid phase occurs at P-T conditions between 10 bar-180 °C and 1 bar-10 °C. The carbon mass and isotopic balance of spring waters of the French Massif Central allow us to compute a total deeply-sourced CO2 emission rate of 1.52 ± 0.14 × 109 mol yr−1, suggesting that the CO2 release from passive rift systems is significant at global scale and should be considered in the present-day global Earth degassing budget. The comparison of our data to other continental rift systems shows a high variability of CO2 emission rates, highlighting that more detailed studies are needed to constrain the CO2 flux from this geodynamic setting that, at present, is likely underestimated.

The Origin and Differentiation of CO2-Rich Primary Melts in Ocean Island Volcanoes: Integrating 3D X-Ray Tomography with Chemical Microanalysis of Olivine-Hosted Melt Inclusions from Pico (Azores).

ABSTRACT Constraining the initial differentiation of primary mantle melts is vital for understanding magmatic systems as a whole. Chemical compositions of olivine-hosted melt inclusions preserve unique information about the mantle sources, crystallisation behaviour and volatile budgets of such melts. Crucially, melt inclusion CO2 contents can be linked to mantle CO2 budgets and inform us on Earth's carbon fluxes and cycles. However, determining total inclusion CO2 contents is not straightforward, as they often need to be reconstructed from CO2 dissolved in melts and CO2 stored in a vapour bubble. Here, we improve upon existing reconstruction methods by combining 3D X-ray computed tomography (CT) with geochemical microanalyses of major, trace and volatile elements. We show that in comparison to CT data, traditional reconstruction methods using 2D photomicrographs can underestimate CO2 budgets by more than 40%. We applied our improved methods to basaltic olivine-hosted melt inclusions from Pico volcano (Azores) in order constrain the formation and differentiation of volatile-rich primary melts in the context of a mantle plume. Results for these inclusions yielded 1935 to 9275 μg/g reconstructed total CO2, some of the highest values reported for ocean island volcanoes to date. Using these CO2 concentrations, we calculate entrapment pressures of 105 to 754 MPa that indicate a magma reservoir comprising stacked sills straddling the crust–mantle boundary. In the magma reservoir, crystallisation of volatile saturated melts drives extensive degassing, leading to fractionated CO2/Ba ratios of 3.5 to 62.2 and a loss of over 79% of primary mantle-derived CO2. Variabilities in trace elements (La, Y) show that differentiation occurred by concurrent mixing and crystallisation of two endmember melts, respectively depleted and enriched in trace elements. Geochemical models show that enriched endmember melts constitute 33 wt % of all melts supplied to the crust at Pico and that primary melts underwent 60% crystallisation prior to eruption. Mantle melting models indicate that the enriched and depleted primary melt endmembers are low- and high-degree melts of carbon-poor lherzolite and carbon-rich pyroxenite, respectively. Moreover, since deep magmas at Pico island are dominantly pyroxenite derived, their CO2-enrichement is mainly controlled by mantle source carbon content. Overall, our study illustrates that by combining 3D imaging, geochemical microanalyses and numerical modelling, melt inclusions provide a unique record of differentiation and storage of deep magmas, as well as mantle melting.

Relative Abundances of CO2, CO, and CH4 in Atmospheres of Earth-like Lifeless Planets

Carbon is an essential element for life on Earth, and the relative abundances of major carbon species (CO2, CO, and CH4) in the atmosphere exert fundamental controls on planetary climate and biogeochemistry. Here we employed a theoretical model of atmospheric chemistry to investigate diversity in the atmospheric abundances of CO2, CO, and CH4 on Earth-like lifeless planets orbiting Sun-like (F-, G-, and K-type) stars. We focused on the conditions for the formation of a CO-rich atmosphere, which would be favorable for the origin of life. Results demonstrated that elevated atmospheric CO2 levels trigger photochemical instability of the CO budget in the atmosphere (i.e., CO runaway) owing to enhanced CO2 photolysis relative to H2O photolysis. Higher volcanic outgassing fluxes of reduced C (CO and CH4) also tend to initiate CO runaway. Our systematic examinations revealed that anoxic atmospheres of Earth-like lifeless planets could be classified in the phase space of CH4/CO2 versus CO/CO2, where a distinct gap in atmospheric carbon chemistry is expected to be observed. Our findings indicate that the gap structure is a general feature of Earth-like lifeless planets with reducing atmospheres orbiting Sun-like (F-, G-, and K-type) stars.

A top-down estimation of subnational CO2 budget using a global high-resolution inverse model with data from regional surface networks

Top-down approaches, such as atmospheric inversions, are a promising tool for evaluating emission estimates based on activity-data. In particular, there is a need to examine carbon budgets at subnational scales (e.g. state/province), since this is where the climate mitigation policies occur. In this study, the subnational scale anthropogenic CO2 emissions are estimated using a high-resolution global CO2 inverse model. The approach is distinctive with the use of continuous atmospheric measurements from regional/urban networks along with background monitoring data for the period 2015–2019 in global inversion. The measurements from several urban areas of the U.S., Europe and Japan, together with recent high-resolution emission inventories and data-driven flux datasets were utilized to estimate the fossil emissions across the urban areas of the world. By jointly optimizing fossil fuel and natural fluxes, the model is able to contribute additional information to the evaluation of province–scale emissions, provided that sufficient regional network observations are available. The fossil CO2 emission estimates over the U.S. states such as Indiana, Massachusetts, Connecticut, New York, Virginia and Maryland were found to have a reasonable agreement with the Environmental Protection Agency (EPA) inventory, and the model corrects the emissions substantially towards the EPA estimates for California and Indiana. The emission estimates over the United Kingdom, France and Germany are comparable with the regional inventory TNO–CAMS. We evaluated model estimates using independent aircraft observations, while comparison with the CarbonTracker model fluxes confirms ability to represent the biospheric fluxes. This study highlights the potential of the newly developed inverse modeling system to utilize the atmospheric data collected from the regional networks and other observation platforms for further enhancing the ability to perform top-down carbon budget assessment at subnational scales and support the monitoring and mitigation of greenhouse gas emissions.

Net effect of chemical erosion in a tropical basin on carbon cycle: Constraints from elemental and sulfur isotopic composition of the Mahanadi river water

Chemical erosion in river basins influence the climate by both consuming (via silicate erosion and carbon burial) and releasing (via H2SO4-mediated carbonate weathering and organic oxidation) atmospheric CO2. Net erosional effect of a basin on carbon cycle, therefore, requires precise rate assessment of all these pathways; combined data for the four processes for a given basin are sparse. In this contribution, we have quantified these process intensities for a large tropical basin (Mahanadi river) from the eastern part of India using new time-series (weekly) data for dissolved major ions and sulfur isotopes, and compiled data for rhenium concentrations and particulate carbon isotopes for the basin. The discharge-weighted silica concentrations (∼215 μM) of these samples is higher than that reported as global average for rivers (∼145 μM), indicating intense silicate erosion in the basin. The δ34S of the riverine sulfates vary between 8.8 ‰ and 17 ‰, with a discharge-weighted average of 12 ± 4 ‰ (global riverine value ∼4.4 ± 4.5‰). Temporal changes in concentrations for most of the elements (and δ34S) show relatively higher (enriched) values during lean-flow stages. Mass balance calculations involving Ca, Mg and Si values confirm that these seasonal changes are mainly due to increase (by 18 ± 9%) of groundwater supply to the stream during non-monsoon seasons. The silicate-derived cations (Catsilicate) for the Mahanadi show minimal changes during monsoon (36 ± 5%) and non-monsoon (33 ± 8%) seasons. These data correspond to a CO2 consumption rate of 2.4 ± 1.6 tC/km2/yr, which is about two times higher than that reported for global rivers. Comparison of δ34S values of riverine sulfate with its possible sources computes the relative supply of sulfates from atmospheric deposition (38%), gypsum (46%), and sulfides (16% (a lower limit)) to the river. The minimal contribution via sulfide oxidation confirms low CO2 release (0.1 ± 0.1 tC/km2/yr) in this basin through sulfuric-acid mediated carbonate weathering. Average rhenium for this river is 5 ± 3 pmol/kg. The source apportionment using S/Re and Na/Re ratios indicates that 85 ± 10% of the Re is derived through organic oxidation. The rhenium data are used to estimate the CO2 release rate (0.50 ± 0.57 tC/km2/yr) by oxidation of petrogenic carbon, which is higher than the estimated organic burial rate (0.27 ± 0.12) for the basin. The estimated four erosion rates confirm a net negative (∼ − 2.1 ± 1.7 tC/km2/yr) effect of chemical erosion in the Mahanadi basin on the CO2 budget. Low sulfide-oxidation in this supply-limited regime is possibly linked to limited exposure of fresher minerals, whereas high silicate erosion in the basin is consistent with its silicate-dominated lithology and tropical climate.

Hydrochemistry and carbon isotope characteristics of Nujiang River water: Implications for CO2 budgets of rock weathering in the Tibetan Plateau

Hydrochemistry and carbon isotope characteristics of Nujiang River water: Implications for CO2 budgets of rock weathering in the Tibetan Plateau

Adapting the marine stewardship council's risk-based framework to assess the impact of towed bottom fishing gear on blue carbon habitats.

Wild capture fisheries are of economic and social importance, providing a primary source of protein to people globally. There is a broad research base on the environmental impacts of fishing gears and processing methods yet, the impact on the global CO2 budget is less well studied. Evaluating the risk that wild capture fisheries pose to ecosystem health is vital to sustainably managing fishing practices to meet increasing global nutritional needs and reverse declines in marine biodiversity. At the same time meeting net-zero ambitions by reducing direct and indirect GHG emissions is vital. Ecological risk assessments, trait-based assessments, and vulnerability assessments have long supported fisheries management systems globally but do not yet provide any representation regarding the impacts that fishing gears have on the ability of the habitat to capture and store carbon. Considering the importance of accessibility and transparency in approaches necessary for fisheries sustainability certifications, this paper describes a method to integrate habitat carbon capacity attributes into the Marine Stewardship Council (MSC) Consequence and Spatial Analysis (CSA) framework. Applying the CSA carbon extension developed herein produces different CSA risk scores compared to the MSC CSA that does not account for carbon. This has potential consequences for certification schemes as carbon becomes more important in the fisheries sustainability conversation. The CSA carbon extension tool developed here is an important first step in incorporating carbon indicators into evaluations of fisheries that consider fishery carbon impacts.

Carbon dioxide exchange in an idealized valley

On a global scale the budget of carbon dioxide (CO2) bears a substantial uncertainty, which is commonly understood to be mainly due to land-surface exchange processes. In this paper it is examined to what extent mountainous model topography can amplify these land-surface exchange processes. The underlying hypothesis is that, on the meso-scale, topography adds additional atmospheric mechanisms that drive the exchange of CO2 at the surface.This model sensitivity study represents an advancement in model development through the implementation of a pioneering combination of the Weather Research and Forecasting (WRF) model, coupled with the Community Land Model (CLM4) to account for photosynthesis, and the semi-empirical TPGPP-LAI model to address ecosystem respiration. An idealized sine-shaped valley is investigated to examine the effect of complex topography on the CO2 budget compared to flat terrain. The systematic variation of meteorological initial conditions and plant functional types create an ensemble that unveils the fundamental factors which dominate the differences of CO2 fluxes between simulations with topography compared to a flat reference surface.During daytime, when there is photosynthesis, the vegetation temperature of the hypothetical sub-grid scale valley is on average 0.7 K colder and its vapor pressure deficit is 0.8 hPa lower which results in stronger net ecosystem exchange. During nighttime the valley is 0.6 K warmer than the plain, which increases ecosystem respiration compared to the plain. Over 24 h the valley is 0.1 K colder, but it acts as a sink of CO2 as the two opposing processes, during daytime and at night, result in 0.2 gC m−2 d−1 stronger net ecosystem exchange in the valley. During daytime differences are caused implicitly by meso-scale circulations through a secondary effect, as slope-winds shape the vertical temperature and humidity profiles, whereas at night the larger surface area of the valley is the prime cause for the differences. In contrast, the effect of differences in ambient CO2 on the ecosystem exchange is negligible.

Ecosystem CO2 Exchange and Its Economic Implications in Northern Permafrost Regions in the 21st Century

AbstractClimate warming increases carbon assimilation by plant growth and also accelerates permafrost CO2 emissions; however, the overall ecosystem CO2 balance in permafrost regions and its economic impacts remain largely unknown. Here we synthesize in situ measurements of net ecosystem CO2 exchange to assess current and future carbon budgets across the northern permafrost regions using the random forest model and calculate their economic implications under the Shared Socio‐economic Pathways (SSPs) based on the PAGE‐ICE model. We estimate a contemporary CO2 emission of 1,539 Tg C during the nongrowing season and CO2 uptake of 2,330 Tg C during the growing season, respectively. Air temperature and precipitation exert the most control over the net ecosystem exchange in the nongrowing season, while leaf area index plays a more important role in the growing season. This region will probably shift to a carbon source after 2,057 under SSP5‐8.5, with a net emission of 17 Pg C during 2057–2100. The net economic benefits of CO2 budget will be $4.5, $5.0, and $2.9 trillion under SSP1‐2.6, SSP2‐4.5, and SSP5‐8.5, respectively. Our results imply that a high‐emission pathway will greatly reduce the economic benefit of carbon assimilation in northern permafrost regions.

Heat pump-driven adsorption CO2 capture for simple and cost-effective retrofits of coal power plants

Coal-fired power plants emit almost a third of fossil CO2 emissions worldwide, and continued operation of existing plants will consume the entire remaining CO2 budget for 1.5 °C of global warming. Hence, there is an urgent need to rapidly cut emissions from existing power plants. The continuous swing adsorption reactor (CSAR) concept offers a promising solution to this challenge. CSAR uses electrically powered heat and vacuum pumps to drive the CO2 capture process and does not require the extraction of large amounts of steam from the power plant, greatly simplifying the retrofit process. A bottom-up techno-economic assessment of CSAR compared to conventional temperature swing adsorption (TSA) using the same sorbent showed near-identical performance in terms of energy penalty (8.0 for CSAR and 8.2 %-points for TSA) and CO2 avoidance cost (54.1 €/ton for CSAR and 55.4 €/ton for TSA). Hence, retrofitting simplicity is achieved at no extra cost. The assessment also showed that, although new coal-fired power plants are economically unviable in regions with already high CO2 prices, already depreciated plants will be difficult to displace via market forces. For example, the levelized cost of electricity for a coal power plant retrofitted with CSAR drops from 99.2 €/MWh to 68.2 €/MWh when the power plant is already depreciated. When CO2 prices rise, the optimal strategy involves retrofitting plants located close to CO2 storage or utilization opportunities for continued baseload operation, while unabated plants without easy access to storage are used at lower capacity factors to integrate rising shares of variable renewables. Simplified retrofitting via CSAR can facilitate the practical and economical execution of this strategy, achieving rapid decarbonization while minimizing the need for new capital investments and disruptive early asset retirements.

High release of isotopically depleted CO2 and CH4 from the photo-degradation of plastic: A pilot laboratory study

This pilot laboratory study reports the direct release of photochemically derived isotopically depleted CO2 and CH4 from low-density polyethylene (LDPE) under ambient atmospheric conditions. We investigated the release of CO2 and CH4 from two different size fractions of LDPE; coarse (∼10 mm × 7 mm) and fine (∼1.5 mm × 1 mm) pieces. Emissions observed at the end of 45 days incubation experiment were 94 nmol/g CH4 and 20 μmol/g CO2 for coarse plastics, and 242 nmol/g CH4 and 42 μmol/g CO2 for fine plastics kept in 120 ml vials under same natural sunlight conditions. Release of CO2 and CH4 from the LDPE kept under dark conditions was statistically not distinguishable from blanks (vials without plastics), which attests the role of photo-degradation in their release. Further, >2 times increase in the emissions of CH4 and CO2 for fine plastics have important implications as plastic size decreases continuously with their degradation in different environmental compartments. Isotopic composition of carbon (δ13C) of CH4 (−676‰ to – 496‰) and CO2 (−132‰ to −140‰) released from the LDPE shows conspicuously depleted signatures, which may have important implications for studies using δ13C to understand biogeochemical processes in different environmental compartments. The present study necessitates the accountability of CO2 and CH4 release from plastics while studying the biogeochemical cycling of carbon in terrestrial and aquatic environments. More studies with different types and sizes of plastics under different environmental conditions are needed to assess the role of plastics in CO2 and CH4 budget.

Two contrasting years of continuous N[formula omitted]O and CO[formula omitted] fluxes on a shallow-peated drained agricultural boreal peatland

Drained agricultural boreal peatlands comprise a large source of nitrous oxide (N2O) and carbon dioxide (CO2) but a small sink or source of methane (CH4). N2O fluxes have high spatial and temporal variability and are often measured with the chamber technique. Therefore, continuous measurements of N2O fluxes are needed to better understand how N2O emissions are triggered and to reduce the uncertainty of annual N2O budget estimations. Here we present a two-year-long time series of continuous measurements of CO2 and N2O fluxes of a shallow-peated drained agricultural boreal peatland cultivated for grass silage. The fluxes were measured with the area-averaging eddy covariance technique. Several N2O peak events were observed throughout all seasons. The peaks were associated with meteorological or management events, such as soil thawing or freezing, precipitation, fertilization and glyphosate application. The annual N2O budget was 4.74 ±0.47 and 6.08 ±0.49 kg N2O-N ha−1 y−1 in 2020 and 2021, respectively. The annual CO2 budget, comprising the sum of net ecosystem exchange and biomass export, was 3.70 ±0.22 and 5.54 ±0.33 t CO2-C ha−1 y−1 in 2020 and 2021, respectively. The N2O budget during the first, warmer winter was 106% higher than during the second, meteorologically more typical winter, due to the higher frequency of soil freezing–thawing cycles. The average annual N2O budget was 36%–50% lower than the IPCC Emission Factor (EF) while the CO2 budget was in accordance with the IPCC EF. CO2 emissions dominated the total CO2-eq emissions of our site but N2O also had a significant contribution of 12%. Our results also suggest that glyphosate application enhanced N2O emissions in the last quarter of 2021. However, the full rotation should be measured to confirm whether there is a need to re-evaluate the N2O IPCC EF for ‘grassland drained boreal’ land-use class.

Direct solar FTIR measurements of CO2 and HCl in the plume of Popocatépetl Volcano, Mexico

Volcanic CO2 emissions inventories have great importance in the understanding of the geological carbon cycle. Volcanoes provide the primary pathway for solid-earth volatiles to reach the Earth’s atmosphere and have the potential to significantly contribute to the carbon-climate feedback. Volcanic carbon emissions (both passive and eruptive degassing) included in inventories, largely stem from patchy surface measurements that suffer from difficulties in removing the atmospheric background. With a 27-year-long ongoing open-vent eruption, Popocatépetl ranks as one of the highest permanent volcanic CO2 emitters worldwide and provides an excellent natural laboratory to design and experiment with new remote sensing methods for volcanic gas emission measurements. Since October 2012, infrared spectra at different spectral regions have been recorded with a solar occultation FTIR spectrometer. The near-infrared spectra allow for high precision measurements of CO2 and HCl columns. Under favorable conditions, the continuous observations during sunrise allow the reconstruction of a plume cross-section of HCl and the estimation of the emission flux using wind data. Despite that the detection of CO2 is more challenging, on April 26th, 2015 we captured a volcanic plume under favourable wind conditions which allowed us to reconstruct from this particular event a CO2 emission rate of 116.10 ± 17.2 kg/s. The volcanic HCl emission on this event was the highest detected during the 2012-2016 period. An annual average CO2 emission estimate of (41.2 ± 16.7) kg/s ((1.30 ± 0.53) Tg/yr) could be determined from a statistical treatment of the detected CO2 and HCl columns in the IR spectra, and their corresponding molecular ratios, during this period. A total of 25 events were used to derive a mean CO2/HCl molecule ratio of 11.4 ± 4.4 and an average HCl emission rate of (3.0 ± 0.3) kg/s could be determined. The CO2 emissions of Popocatépetl were found to be around 0.32% of the total anthropogenic CO2 emissions reported in the country and 3.6% of those corresponding to the Mexico City Metropolitan Area (MCMA). CO2 emissions from the Popocatépetl volcano can be considered to play a negligible role in the global CO2 budget, but should be taken into account.

ENSO Impact on the Declining CO2 Sink Rate

The ocean and land processes which determine the rate of uptake of anthropogenic carbon dioxide emissions are many and complex. Simplified models of the net effect of all these processes can assist in the development of more detailed models. A simple time-dependent atmospheric CO2 budget model is shown to closely match yearly Mauna Loa CO2 concentrations during 1959-2021. The model assumes an anthropogenic CO2 source, and a constant yearly CO2 sink rate proportional to the excess of CO2 over a baseline equilibrium value determined by the Mauna Loa data. The yearly CO2 sink rate is found to be 2.02% of the atmospheric excess above 293.6 ppm, with a downward trend in the sink rate during 1959-2021 that disappears when El Niño – Southern Oscillation (ENSO) activity is empirically accounted for. Significant model departures from observations occurred for three years after the 1991 eruption of Mt. Pinatubo. Assuming no change in the sink rate, the latest Energy Information Administration CO2 global emissions projections to 2050, and extrapolated to 2100, lead to model-projected CO2 concentrations well below the highest Representative Concentration Pathways scenario RCP8.5.

Modelling CO2 budget of mussel farms across the Mediterranean Sea.

The role of bivalve aquaculture as a carbon sink is highly debated, without a general consensus on the components to include in the budget. This study proposes to estimate the terms of the budget using a scope-for-growth-based model. The model was applied at 12 Mediterranean sites, with environmental forcings provided by operational oceanography data spanning over 12 years. Mussels were found to be slight sinks, with a limited variability across sites, if all components of the budget, i.e. accumulation in soft tissue, emissions associated with calcification and respiration, are included. The differences found among stations concerning the calcification and soft tissue contributions to the budget were found to be related to site-specific productivity and water chemistry parameters. This led to the identification of a set of meta-models, which could be used for relating the budget to local conditions, at a screening level, rendering them useful for optimal site selection.

Metabolism and carbonate buffering drive seasonal dynamics of CO2 emissions from two German reservoirs

Biological metabolism drives much of the variation in CO2 in terrestrial ecosystems but does not explain CO2 oversaturation and emission in net autotrophic lakes and reservoirs. The unexplained CO2 could be attributed to the equilibria between CO2 and the carbonate buffering system, which is seldom integrated into CO2 budgets, let alone its interplay with metabolism on CO2 emissions. Here, we perform a process-based mass balance modeling analysis based on an 8-year dataset from two adjacent reservoirs with similar catchment sizes but contrasting trophic states and alkalinity. We find that in addition to the well-acknowledged driver of net metabolic CO2 production, carbonate buffering also determines the total amount and seasonal dynamics of CO2 emissions from the reservoirs. Carbonate buffering can contribute up to nearly 50% of whole-reservoir CO2 emissions, by converting the ionic forms of carbonate to CO2. This results in similar seasonal CO2 emissions from reservoirs with differing trophic state, even in low alkalinity system. We therefore suggest that catchment alkalinity, instead of trophic state, may be more relevant in predicting CO2 emissions from reservoirs. Our model approach highlights the important role of carbonate buffering and metabolism that generate and remove CO2 throughout the reservoirs on a seasonal scale. The inclusion of carbonate buffering could diminish a major uncertainty in the estimation of reservoir CO2 emissions and increase the robustness of aquatic CO2 emission estimates.

A Fair Share of Carbon: Some countries are using too much of the world's CO2 budget.

A Fair Share of Carbon: Some countries are using too much of the world's CO2 budget.

Regional Atmospheric CO2 Response to Ecosystem CO2 Budgets in China

The distribution of atmospheric CO2 is not homogenous, primarily due to variations in the CO2 budgets of regional terrestrial ecosystems. To formulate a comprehensive strategy to combat the increasing global CO2 levels and associated warming, it is crucial to consider both the distribution of atmospheric CO2 and the CO2 budgets of ecosystems. This study focused on analyzing the relationship between regional atmospheric CO2 and CO2 budgets in China from 2010 to 2017. Initially, a robust estimation model of net ecosystem CO2 exchange was developed to calculate CO2 budgets using collected emission data. Subsequently, Pearson correlation, redundancy analysis, and geographically weighted regression techniques were employed to examine the link between atmospheric CO2 levels, CO2 budgets, and other meteorological factors at various spatial and temporal scales. The findings from the redundancy analysis and geographically weighted regression indicated that the atmospheric CO2 content of each province could not be solely determined by the regional CO2 budgets. However, a significant and positive correlation between atmospheric CO2 levels and CO2 budgets was observed in non-coastal provinces for a period of six months (R2 ranging from 0.46 to 0.83). Consequently, it is essential to promote a balance between CO2 emissions and the CO2 uptake capacity of regional ecosystems. This balance would minimize positive CO2 budgets and effectively mitigate the increase in atmospheric CO2 levels.

Radiocarbon evidence for the stability of polar ocean overturning during the Holocene

Proxy-based studies have linked the pre-industrial atmospheric p_{{rm{CO}}_{2}} rise of ∼20 ppmv in the mid- to late Holocene to an inferred increase in the Southern Ocean overturning and associated biogeochemical changes. However, the history of polar ocean overturning and ventilation through the Holocene remains poorly constrained, leaving important gaps in the assessment of the feedbacks between changes in ocean circulation and the carbon cycle in a warm climate state. The deep-ocean radiocarbon content, which provides a measure of ventilation, responds to circulation changes on centennial to millennial time scales. Here we present absolutely dated deep-sea coral radiocarbon records from the Drake Passage, between South America and Antarctica, and Reykjanes Ridge, south of Iceland, over the Holocene. Our data suggest that ventilation in the Antarctic circumpolar waters and North Atlantic Deep Water is surprisingly invariant within proxy uncertainties at our sampling resolution. Our findings indicate that long-term, large-scale polar ocean overturning has not been disturbed to a level resolvable by radiocarbon and is probably not responsible for the millennial atmosphere p_{{rm{CO}}_{2}} evolution through the Holocene. Instead, continuous nutrient and carbon redistribution within the water column following deglaciation, as well as changes in land organic carbon stock, might have regulated atmospheric CO2 budget during this period.

High-resolution GEOS-Chem model for Indian monsoon region: Seasonal cycle and budget of tropospheric CO2

A nested GEOS-Chem atmosphere transport model has been set up for the Indian monsoon region (40° E-110° E & 15° S–45° N at 0.250X0.3125°) spatial resolution to study the variability of the tropospheric CO2 over India and surrounding oceans during 2012–2020. The model has been constrained by the influxes of CO2 at its four lateral boundaries derived from the GEOS-Chem global simulations and surface fluxes of CO2 over the land and oceans based on historical databases. It is initialized from a known state and driven by the GEOS reanalysis's meteorological forcing. Model simulations were evaluated at three in situ measurement locations and with respect to the satellite retrievals from OCO-2 and GOSAT. Model parameters were tuned to have reasonable solutions to resolve observed latitudinal gradient and seasonal and inter-annual variability. Three additional model runs were made to evaluate the role of long-range transport, net terrestrial ecosystem exchange, air-sea fluxes, and regional emissions in controlling seasonal oscillations of tropospheric CO2 over the study region. It revealed that the net terrestrial ecosystem exchanges are responsible for 35% control in the surface layer CO2 seasonal tendency for India and the Bay of Bengal domains, and 10% for the Arabian Sea. The air-sea fluxes have 8% control on the CO2 seasonal tendency for the Arabian Sea and Bay of Bengal and 5% for India. The anthropogenic emissions have 4% control for India and <1% for the Arabian Sea, and 9% for the Bay of Bengal. The long-range transport, as the residual, is responsible for 60% variability in the seasonal cycle of CO2 over India and the Bay of Bengal and 75% for the Arabian Sea domain.