Africa contributes significantly to the global greenhouse gases (GHG) budget through extensive land use change that is driven by rapid population growth and low human development status. As part of the REgional Carbon Cycle Assessment and Processes Phase 2 (RECCAP2) project, we developed a comprehensive GHG budget for the period 2009-2019 for Africa. We considered bottom-up process-based models, data-driven remotely sensed products, and national greenhouse gas inventories in comparison with top-down atmospheric inversions, accounting also for lateral fluxes. We incorporated emission estimates derived from novel methodologies for termites, herbivores, and fire, which are of particular importance in Africa. We further constrained global biomass change products with high-quality local observation data. During the RECCAP2 period, Africa remains a net sink for carbon. Emissions from land cover change represents the largest contribution to the African budget. However, land cover change emissions in the drier savanna regions were largely offset by increased vegetation growth in the wet tropics. Additionally, fire emissions decreased as suggested by strong reductions in burned area. Burning of fuelwood has however increased. As expected, an upward trend in anthropogenic fossil fuel emissions was evident, ascribed to an increasing demand for energy by a growing and developing population. For all the component fluxes, uncertainty and interannual variability is large, which highlights the need for increased efforts to address Africa-specific data gaps. However, for RECCAP2, we have improved our overall understanding of many of the important components of the African GHG budget that will help to inform climate policy and action.

How to cite: Ernst, Y. and Archibald, S. and the RECCAP2 Africa team: The African greenhouse gases budget: flux trends and uncertainties for the 2009-2019 period, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-606, https://doi.org/10.5194/egusphere-egu23-606, 2023.

Understanding climate change and possible solutions to recent increases in concentrations of major GHG concentrations dependent upon quantifying the emission inventory of these gases. The objective of this study, which is part of the Regional Carbon Cycle Assessment and Processes-2 (RECCAP2) project, is to estimate the country-specific GHGs budget (sources and sinks) for the South Asia (SA) region for the 2010s. The region comprises seven countries: Afghanistan, Bangladesh, Bhutan, India, Nepal, Pakistan, and Sri Lanka. Each country in the region is experiencing rapid changes due to the continuous development of agriculture, deforestation, reforestation, afforestation, and the increased demand for land for people to live in. In this study, we synthesize top-down (TD) and bottom-up (BU) model results and ground-based and other data sets to estimate the GHG emissions for carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) due to anthropogenic and natural biospheric activities. Major contributing factors include net biome productivity, fossil fuel emissions, inland waters, and wetland and wet/dry soils. Our study shows that the SA region was the net source of atmospheric CO2 for the 2010s. BU estimates for CO2, CH4, and N2O emissions were 1974, 1047, and 715 Tg CO2eq, and TD estimates were 2010, 1247, and 799 Tg CO2 eq. The total GHG emission for the region based on BP and TD were 3736 and 4056 Tg CO2 eq. Among SA countries, India was the most significant contributor to the total GHG emission.

How to cite: Jain, A., Anand, J., Chandra, N., and Patra, P.: Greenhouse gas budget for South Asia region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16920, https://doi.org/10.5194/egusphere-egu23-16920, 2023.

Accurate national carbon budget assessments allow nations to evaluate their progress in cutting carbon emissions and therefore be aligned with the Paris Climate Agreement goals. To support the initiative of The REgional Carbon Cycle Assessment and Processes (RECCAP-2), we built a synthesis of the Australasia (Australia and New Zealand) terrestrial carbon budget for 2010-2019 based on top-down and bottom-up approaches. Major carbon flux components in the bottom-up budget (e.g., net primary productivity and heterotrophic respiration) were simulated by CABLE model, Biome-BGC model and Cewn simulations. In addition, this budget include carbon flux components from the land-ocean aquatic continuum, such as inland waters, estuaries, blue carbon ecosystems, and continental shelves and carbon fluxes embodied in trade (export and import) of crops, woods, livestock and fossil fuel. We reconciled Australia and New Zealand bottom-up budgets separately with fluxes derived from regional and global OCO-2, GOSAT flux inversions, as well as fluxes obtained from in-situ measurement only (CarbonWatchNZ). We found that annual mean budgets for Australia agree relatively well (within the uncertainty range) with regional and global top-down GOSAT and OCO-2 flux estimates. New Zealand's annual bottom-up carbon budget also agrees relatively well with fluxes derived from CarbonWatchNZ inversion and GOSAT but disagrees with global flux estimates from OCO-2.

How to cite: Villalobos, Y., Canadell, P., Briggs, P., Harman, I., Keller, E. D., Bukosa, B., Mikaloff-Fletcher, S. E., Smith, B., Kirschbaum, M. UF., Giltrap, D., Liang, L., Lauerwald, R., Rosentreter, J., Maavara, T., Resplandy, L., Rayner, P. J., Schöemann, E., and Basu, S.: A comprehensive synthesis of anthropogenic and natural sources and sinks of Australasia carbon budget (2010-2019), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15006, https://doi.org/10.5194/egusphere-egu23-15006, 2023.

Land-based mitigation is essential in reducing carbon emissions. Yet, the attribution of land carbon fluxes to their sinks and sources remains highly uncertain, in particular for the forest-rich but data-poor region of Eastern Europe. Here we integrate various data sources (from top-down and bottom-up modelling, earth observation, inventories) to show that Eastern Europe accounted for an annual aboveground biomass (AGB) carbon sink of ~0.49 GtC in 2010‑2019, or about 75% of the entire European carbon uptake. However, we find that the land-based carbon sink is declining. This declining trend is mainly driven by changes in land use and land management, but also by increasing natural disturbances due to ongoing climate change. Despite the high overall importance of environmental factors such as soil moisture, nitrogen and CO₂ for enhancing the land-based carbon sink, we find indicators of a saturation effect of the regrowth in abandoned former agricultural areas, combined with an increase in wood harvest, particularly in European Russia. Our results contribute to a better understanding of the regional carbon budget of Eastern Europe and its trend. This study sheds light on land use and management as drivers of the land-based carbon sink and their role for climate mitigation.

How to cite: Winkler, K., Yang, H., Ganzenmüller, R., Fuchs, R., Ceccherini, G., Duveiller, G., Grassi, G., Pongratz, J., Bastos, A., Shvidenko, A., Araza, A., Herold, M., and Ciais, P.: Impacts of land use and environmental change on the Eastern European land carbon sink, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13792, https://doi.org/10.5194/egusphere-egu23-13792, 2023.

The Amazon is the largest continuous tropical forest in the world and plays a key role in the global carbon cycle. Human-induced disturbances (e.g., deforestation and wildfires) in combination with climate change have impacted its carbon cycling. However, uncertainties remain on the magnitude of carbon fluxes associated with human-induced disturbances and the old-growth forest sink, and thus the net land carbon balance of the Amazon. Here we synthesize state-of-the-art estimates of the land carbon flux components in the Amazon. To quantify the human-disturbance fluxes from deforestation, land use and land cover changes and degradation, we use a set of bookkeeping models. The annual intact sink was quantified using a set of 16 Dynamic Global Vegetation Models (DGVMs). We then combine the carbon flux estimates from disturbances with the intact sink estimates to provide a bottom-up estimate of the net land carbon flux and compare them alongside top-down estimates from atmospheric model inversions. Between 2010 and 2018, the net land carbon flux in the Brazilian Amazon estimated with the bottom-up approach was -59 (±160) Tg C yr^-1 and +36 (±125) Tg C yr^-1 with the top-down approach. Despite disagreeing on the sign of the flux, this analysis suggests that the Brazilian Amazon was on average near carbon neutral over the 2010-2018 period, given the large uncertainties underlying both methods. The net land carbon fluxes for the years 2019 and 2020 based on the bottom-up approach were larger than for 2010-2018. This is likely primarily due to direct emissions related to an increase in deforestation although it may possibly be partly caused by a weakening of the forest carbon sink, both in response to deforestation and a warming climate. Spatially, both methodologies agree that the south-eastern Amazon was a net carbon source over the whole study period. These results have important implications for the mitigation potential of Brazilian ecosystems within the goals of the Paris Agreement. 

How to cite: Rosan, T. M., Sitch, S., O’Sullivan, M., Wilson, C., Basso, L. S., Fawcett, D., Heinrich, V. A., Souza, J. G., von Randow, C., Mercado, L. M., Gloor, E., Gatti, L., Friedlingstein, P., Wiltshire, A., Pongratz, J., Schwingshackl, C., and Aragão, L. E. O. C. and the TRENDY-v11 Team: The contemporary Amazon Forest carbon budget, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3228, https://doi.org/10.5194/egusphere-egu23-3228, 2023.

Fires in the tropics are linked to both climate and land-use change. While in the Amazon, deforestation-related fires decreased following a substantial reduction in deforestation activities until 2012, there have been recent upturns in deforestation and forest fires. Furthermore, earth system models predict a further increase in the intensity of dry seasons in this region in the 21st century. Therefore, carbon emissions from drought-induced forest fires can counteract further pledged deforestation reductions in the following decades, yet they are only partially accounted for in national carbon emission estimates. Improved assessments of fire impacts, including the carbon fluxes arising from post-fire mortality and regrowth, are therefore highly important. 
Combining a range of available satellite products enables spatially specific fire emissions estimations. We developed a remote sensing based approach where biomass maps, observed forest loss, burned area and active fire data are combined to generate updated fuel load and emission estimates. In addition, space-for-time methods are employed to derive estimates of post-fire mortality as a function of pre-fire biomass. This high-resolution model guarantees an improved separation of fire types, and we can report emissions associated with deforestation, forest degradation and savanna fires for the entire Amazon basin and the Brazilian Cerrado at monthly intervals. 
Results show that over 2015-2020 fires cause annual gross emissions of ~300 Tg C over the Amazon and Cerrado. While instantaneous emissions from forest fires are small, the fire-induced mortality and subsequent decomposition cause legacy fluxes which are closer to deforestation fire emissions in magnitude, highlighting their importance. Recent upturns in deforestation fire emissions were observed, including in conservation areas established before 2004. There is overall good agreement with previous instantaneous fire emission estimates from other approaches (GFED4s, GFED 500 m) while remaining disagreements highlight areas of uncertainties, such as combustion completeness values, which could benefit from additional field measurements and spatial modelling supported by EO products.
Outputs from this work can further be used to improve regional greenhouse gas budgets and inform emission reduction and mitigation efforts.

How to cite: Fawcett, D., Ng, L., Tai, A., Yan, X., Rosan, T., Silva Junior, C., Bastos, A., Ciais, P., Albergel, C., Aragão, L., and Sitch, S.: Carbon fluxes from different fire types in the Amazon and Cerrado biomes quantified using Earth-observation based modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6173, https://doi.org/10.5194/egusphere-egu23-6173, 2023.

Wildfires are an integral part of boreal forest dynamics. Understanding the carbon loss/recovery associated with fires is crucial to assess the stability of these slow-growing forests.  Yet, the carbon balance from fires and post-fire forest recovery remain uncertain at the biome scale due to the lack of spatial details about rates of forest regrowth. Here, we quantify carbon losses from fire emissions and gains from post-fire regrowth using high spatial-resolution satellite data and a bookkeeping model. We combined a 35-year long record of burned area from the Landsat satellites since 1985 with local biomass-age regrowth curves derived from high-resolution satellite-based above ground biomass (AGB) datasets. We found that forests in Eurasia tend to recover faster and reach higher biomass levels than those in North America. Young forests recovering from post-1985 wildfires produced a carbon sink of 652±200 TgC during the period 1985 to 2020. The additional recovery of older secondary forests that burned before 1985 further adds a cumulative sink of 1659±346 TgC. Comparatively, old-growth forests that did not burn accumulated 930±233 TgC during the period 1985-2020. This result shows 71% of the contemporary carbon sink in AGB is contributed by recovery from fires. After accounting for fire emissions each year and for the slow decay of coarse woody debris after burning, the net AGB carbon sink in boreal forests is 2108±234 TgC during 1985-2020. This study provides the first spatially explicit aboveground observation-based carbon budget of boreal forests and provides insights on the key factors that will control its future evolution.

How to cite: Xu, Y., Ciais, P., Li, W., Saatchi, S., Santoro, M., Cescatti, A., Shchepashchenko, D., He, G., Guido, C., He, J., Fan, L., Brandt, M., Fensholt, R., Wigneron, J.-P., Kay, H., Sitch, S., Bastos, A., Bowing, S., Ritter, F., and Fayad, I.: Biomass recovery after fires dominates the carbon sink of boreal forests over the last three decades, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9695, https://doi.org/10.5194/egusphere-egu23-9695, 2023.

Methane (CH₄) levels in the atmosphere increased by 15.1 ± 0.4 ppb in 2020, the highest annual increase from 1984 to 2020, despite a likely decrease in anthropogenic CH₄ emissions during COVID-19 confinements. Here, we used bottom-up and top-down methods to quantify the changes in different sources of CH₄, and in its atmospheric sink due to the hydroxyl radical (OH) in 2020 compared to 2019. Bottom-up methods showed that, globally, total anthropogenic emissions slightly decreased by ~1.2 Tg CH₄ yr^-1, fire emissions were lower than in 2019 by ~6.5 Tg CH₄ yr^-1, and wetland emissions increased by 6.0 ± 2.3 Tg CH₄ yr^-1. In addition to higher wetland emissions in 2020 than 2019 from bottom-up, we found a decrease of 1.6–1.8% in tropospheric OH concentration relative to 2019, mainly due to lower anthropogenic NO_x emissions and associated lower free tropospheric ozone during the confinements. Based on atmospheric CH₄ observations from the surface network, and considering the decrease in OH, using top-down inversions, we infer that global net emissions increased by 6.9 ± 2.1 Tg CH₄ yr^-1 in 2020 relative to 2019, while the global CH₄ removal from reaction with OH in the atmosphere decreased in 2020 by 7.5 ± 0.8 Tg CH₄ yr^-1. Therefore, we attribute the positive growth rate anomaly of atmospheric CH₄ in 2020 relative to 2019 to lower OH sink (53 ± 10%) and higher natural emissions (47 ± 16%), mostly from wetlands. Warmer and wetter climate conditions in the Northern Hemisphere promoted wetland emissions, but fires decreased in the Southern Hemisphere, compared to the previous year. Our study highlights that northern microbial emissions of CH₄ are highly sensitive to a warmer and wetter climate and could act as a positive feedback in the future. Our study also hints that the global CH₄ pledge must be implemented by taking into account NO_x emissions trend, whose reduction lengthens the lifetime of atmospheric CH₄.

How to cite: Peng, S., Lin, X., Thompson, R., Xi, Y., Liu, G., Lan, X., Hauglustaine, D., Poulter, B., Ramonet, M., Saumois, M., Yin, Y., Zhang, Z., Zheng, B., and Ciais, P.: Why atmospheric methane surged in 2020?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8372, https://doi.org/10.5194/egusphere-egu23-8372, 2023.

Increasing extreme events and drastic shifts in the variability, intensity and frequency of droughts, heavy precipitation and frost are predicted to accompany further climate change. It is most likely that an increasing occurrence of such events will be accompanied by soil feedback of GHG emissions, particularly of nitrous oxide (N₂O) known to be an extremely sensitive GHG. The increase in extreme events can lead to an increased occurrence of short-term emission pulses, referred to as ‘hot moments’, which can contribute significantly to the total annual N₂O emission balance.
To account for this potential feedback to the climate system, biogeochemical models driven by climate projections of multi-model ensembles (CPM) can be used to generate scenarios observing future trends in N₂O emission behavior.
Most commonly, the CPM average is used as climate input in biogeochemical models. While averaging CPM’s may provide the best overall comparison with real mean climate change, it poses the risk of ‘averaging out’ expected extreme events, thereby biasing soil-atmosphere feedbacks and future N₂O emission trends! 

We follow the hypothesis, that for nitrogen-saturated soils as common in industrialized countries, the annual N₂O emissions simulated by the averaged CPM differ from the average annual N₂O emissions simulated by the individual CPM’s, as hot moment inducing extreme climate events are averaged as well.

For our biogeochemical model simulations, we used weather data from ten selected individual climate-projections based on the multi-model ensemble of the EURO-CORDEX initiative. To focus on the effects of climate and to exclude possible biases, remaining input parameters were unified, i.e., homogeneous soil horizons and a single crop rotation were assumed. In addition, each simulation period was initialised with the same parameters to exclude possible changes in fluxes resulting from soil carbon and nitrogen cycling.

First results with CANDY and LDNDC seem to support our hypothesis, showing that annual N₂O emissions simulated with the averaged CPM differ clearly from those resulting from the output mean of the individual CPM’s.

This emphasises to consider using the averaged output based on individual CPM’s rather than relying solely on averaged CPM’s for predicting future N₂O emission trends.

How to cite: Hey, L., F. Jungkunst, H., and H. E. Meurer, K.: A potential bias using averaged climate projection multi model ensembles when forecasting nitrous oxide emissions from soils under climate change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8208, https://doi.org/10.5194/egusphere-egu23-8208, 2023.

Global net biome production (NBP), or net land carbon uptake, has been repeatedly shown to increase during recent decades. However, whether the temporal variability and autocorrelation of NBP has changed during this period remains elusive. Answering this question is particularly relevant given that an increase in both could indicate destabilising C sinks and potentially lead to abrupt changes. We investigated the trends and controls of net land C uptake and its temporal variability and autocorrelation, from 1981 to 2018, using two atmospheric inversion models, the amplitude of the seasonal cycle of atmospheric CO₂ derived from nine monitoring stations distributed across the Pacific Ocean, and 12 dynamic global vegetation models. Spatially, we found that plant biodiversity presented a convex parabolic relationship with NBP and its temporal variability at the global scale while nitrogen deposition generally increased annual NBP. We also found that annual NBP and its interdecadal temporal variability globally increased, but temporal autocorrelation decreased. Regions characterized by increasingly variable NBP were usually with warmer and with increasingly variable temperatures, and lower and weaker trends in NBP compared to those where NBP variability did not increase, where NBP became stronger. Annual temperature increase and its increasing temporal variability were the most important drivers of declining NBP and increasingly its variability. Our results show that increasing regional NBP variability can be mostly attributed to climate change.

How to cite: Fernández-Martínez, M., Peñuelas, J., Chevallier, F., Ciais, P., Obersteiner, M., Rödenbeck, C., Sardans, J., Vicca, S., Yang, H., Sitch, S., Friedlingstein, P., Arora, V. K., Goll, D., Jain, A. K., Lombardozzi, D. L., and McGuire, P. C.: Is destabilisation risk increasing in land carbon sinks?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2813, https://doi.org/10.5194/egusphere-egu23-2813, 2023.

Timely, fine-grained gridded carbon emission datasets are particularly important for global climate change research. Often, fine-grained datasets are challenging to visualize over the globe, and clear visualization tools are also needed. Therefore, we present a near-real-time global gridded daily CO₂ emissions dataset (GRACED). GRACED provides gridded CO₂ emissions at a 0.1° × 0.1° spatial resolution and 1-day temporal resolution from cement production and fossil fuel combustion over seven sectors, including power, industry, residential consumption, ground transportation, domestic aviation, international aviation, and international shipping. GRACED is prepared from the near-real-time daily national CO₂ emissions estimates (Carbon Monitor), multi-source spatial activity data and satellite NO₂ data for time variations of those spatial activity data. Here, we examined the spatial patterns of sectoral CO₂ emission changes from January 1, 2019, to December 31, 2021. In 2021, most regions showed rapid rebounds in carbon emissions compared with 2020, reflecting the continuing challenges to accelerate climate mitigation in the post-COVID era. GRACED provides the most timely and more refined overview than any other previously published datasets, which enables more accurate and timely identification of when and where fossil CO₂ emissions have rebounded and decreased as the world recovers from COVID-19 and witnesses contrasted efforts to decarbonize energy systems. Uncertainty analysis of GRACED gives a grid-level two-sigma uncertainty of value of ±19.9%, indicating the reliability of GRACED was not sacrificed for the sake of higher spatiotemporal resolution that GRACED provides. In addition, we also examined the distribution of emission in a grid-wise perspective for major emission datasets, and compared it with GRACED. The similarity in emission distribution was observed in GRACED and other datasets. One of the advantages of our dataset is that it provides worldwide near-real-time monitoring of CO₂ emissions with different fine spatial scales at the sub-national level, such as cities, thus enhancing our comprehension of spatial and temporal changes in CO₂ emissions and anthropogenic activities. With the continued extension of GRACED time series, we present crucial daily-level input to analyze CO₂ emission changes in the post-COVID era, which will ultimately facilitate and aid in designing more localized and adaptive management policies for the purpose of climate change mitigation in the post-COVID era.

How to cite: Dou, X., Liu, Z., Ciais, P., Hong, J., Chevallier, F., Wang, Y., Yan, F., Davis, S. J., Crippa, M., Janssens-Maenhout, G., Guizzardi, D., Solazzo, E., Song, X., Huo, D., Ke, P., Wang, H., and Deng, Z.: Near-real-time global gridded daily CO2 emissions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3303, https://doi.org/10.5194/egusphere-egu23-3303, 2023.

Keeping global warming in line with the Paris Agreement requires rapid reductions in CO₂ emissions. Tracking these reductions demands a thorough bookkeeping of natural and anthropogenic carbon fluxes. The second REgional Carbon Cycle Assessment and Processes (RECCAP2) activity of the Global Carbon Project aims to accurately assess land and ocean CO₂ sources and sinks through the efforts of hundreds of scientists around the globe. 

For the ocean component, regional budgets are developed for the global ocean and five large regions for the period 1980-2018. In addition, four ‘special focus’ themes, namely the biological carbon pump, the seasonal cycle, the coastal ocean and model evaluation are addressed. We use state-of-the-art ocean models and observation-based datasets to provide robust estimates of regional CO₂ budgets and constrain their uncertainties. Here, we will provide an overview of RECCAP2 activities, and showcase key results focusing on mean ocean carbon fluxes, and their trends and variability.

How to cite: Hauck, J., Gruber, N., Ishii, M., and Müller, J. D. and the RECCAP2 ocean chapter leads: Constraining regional and global ocean carbon fluxes in RECCAP2, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12786, https://doi.org/10.5194/egusphere-egu23-12786, 2023.

The RECCAP2 global ocean project provides an assessment of the mean, trends, and variability of the global ocean carbon sink for the period 1985-2018. The analysis is based on a comprehensive assessment of models and observation-based products, including global ocean biogeochemical models (GOBMs), pCO₂ observation-based air-sea CO₂ flux products, ocean data assimilation models, and DIC-observation based products. We find that the mean ocean CO₂ sink from 1985-2018 is -1.7±0.3 PgC yr^-1 as diagnosed by pCO₂-observation based air-sea CO₂ flux products. The dominant component of the global air-sea CO₂ flux is the oceanic uptake of anthropogenic CO₂, which is estimated at between -2.0 to -2.6 PgC yr^-1 using a range of GOBMs, assimilation models and DIC-based products. The second largest component of the global air-sea CO₂ flux is the outgassing of terrestrially-derived CO₂, which is estimated at 0.65±0.3 PgC yr^-1 but is not yet fully resolved by RECCAP2 models. The trend in the global air-sea CO₂ flux from 1985-2018 ranges from -0.26 PgC yr^-1 decade^-1 in the GOBMs to -0.39 PgC yr^-1 decade^-1 in the pCO₂ products. Over the 2001-2018 period, when the pCO₂-based estimates benefit from improved data coverage, they predict a strengthening trend in the ocean carbon sink of -0.63 PgC yr^-1 decade^-1. This is driven primarily by the trend in anthropogenic carbon uptake of -0.41 PgC yr^-1 decade^-1, and secondarily by a climate-forced trend of -0.28 PgC yr^-1 decade^-1. This climate-forced strengthening of the ocean carbon sink since 2001 is not diagnosed in the GOBMs, and the reasons for this trend remain unclear. We find that the interannual to decadal variability of the global carbon sink is mainly driven by climate variability, with the climate-driven variability exceeding the CO₂-forced variability by 2-3 times. GOBMs suggest that the climate-driven variability is about 4-8% of the global mean carbon sink, while the climate-driven variability is about 9-14% of the global mean flux in the observation-based pCO₂ products. In all, the RECCAP2 analysis provides a state-of-the-art summary of our current knowledge of the ocean carbon sink, and the mechanisms driving its magnitude, trends, and variability over time.

How to cite: DeVries, T., Yamamoto, K., and Wanninkhof, R. and the RECCAP2 Global Ocean Team: Magnitude, trends, and variability of the global ocean carbon sink from 1985-2018, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16842, https://doi.org/10.5194/egusphere-egu23-16842, 2023.

The dynamic and thermohaline characteristics of the Atlantic Ocean linked to the Atlantic Meridional Overturning Circulation (AMOC) give it a specific role in the accumulation of heat and CO₂, either of natural or anthropogenic origin (Cant), from the surface layer to the deep waters, significantly mitigating the impacts of anthropogenic climate change. Here, we evaluate the annual mean, long-term trends, seasonal cycle and interannual variability of net sea-air CO₂ fluxes (FCO₂) between 1985 and 2018 based on observation products (pCO₂-products) and global ocean biogeochemical models (GOBMs) for the Atlantic from 30ºS to the Nordic Seas (~79ºN) and the Mediterranean. The mean contemporary FCO₂ (sum of anthropogenic and natural components) is estimated to be 0.362 ± 0.067 and 0.47 ± 0.15 Pg C yr^-1 using pCO₂-products and GOBMs, respectively. The GOBMs show consistent growth trends in CO₂ uptake with rates similar to the atmospheric CO₂ growth, however trends obtained from CO₂-products show a sharp increase from the pre-2000 period to the post-2000 period. There is overall agreement between pCO₂-products and GOBMs results for mean values, seasonal cycle and interannual variability in all biomes, except for the North Atlantic subpolar biome, where pCO₂-products show lower mean values, larger trends, and a different seasonal cycle than GOBMs. The GOBMs and pCO₂-products show very concordant values in equatorial and subtropical regions, where CO₂ variability is strongly determined by temperature. For the period 1994-2007, GOBMs show concordant values in annual Cant storage rate with carbonate marine system observations (Gruber et al., 2019) with values of 0.506 ± 0.106 Pg C yr^-1 vs 0.673 ± 0.066 Pg C yr^-1, respectively. The Cant storage rate agreement between GOBMs and observations are also registered in the different biomes, although in both permanently stratified subtropical in North and South Atlantic biomes, the storage rates in GOBMs show a larger spread with their mean values 30 and 40% lower than those estimated from observations. In general, the Atlantic accumulates more Cant than that inferred from the cumulative FCO₂ changes, partly due to a significant lateral Cant transport from the Southern Ocean (about 30%).

How to cite: Perez, F. F., Gehlen, M., Tjiputra, J., Olsen, A., Becker, M., Lopez-Mozos, M., Müller, J. D., Goris, N., and Hauck, J.: An assessment of CO2 storage and sea-air fluxes for the Atlantic Ocean and Mediterranean Sea between 1985 and 2018 , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13759, https://doi.org/10.5194/egusphere-egu23-13759, 2023.

Cool temperatures, vigorous overturning circulation, and high biological productivity make the Southern Ocean a key region for the air-sea CO₂ exchanges. It is also the main gateway for anthropogenic CO₂ into the ocean owing to the upwelling of old water masses with low anthropogenic CO₂ concentration, and the transport of the newly equilibrated surface waters into the ocean interior. Here we present results from the Southern Ocean chapter of RECCAP2, which is the Global Carbon Project’s second systematic study on Regional Carbon Cycle Assessment and Processes. We analyse Southern Ocean contemporary carbon fluxes and anthropogenic carbon accumulation in 1985-2018 from a wide range of global ocean biogeochemical models (GOBMs), surface ocean pCO₂-based data products (pCO_2-products), and data-assimilated models, with the aim of identifying patterns of regional and temporal variability, model limitations and future challenges. Our results highlight agreement of GOBMs and pCO₂-products on the mean Southern Ocean contemporary CO₂ uptake (0.75 ± 0.28 PgC yr^-1 and 0.74 ± 0.07 PgC yr^-1 respectively). Compared with RECCAP1 (where the database of model- and observation-based estimates was significantly smaller), the new estimates suggest a weaker sink, possibly due to better representation of winter outgassing. Strong discrepancies exist between GOBMs and pCO₂-products in seasonality and trend estimates between 1985-2018. The pCO₂-products show the presence of a stagnation in uptake through the 1990’s followed by a rapid increase in uptake, while GOBMs show consistent uptake throughout the 1985-2018 period. On a regional level, the subtropical seasonally stratified (STSS) biome has the largest air-sea CO₂ flux with uptake of CO₂ peaking in winter, whereas the ice (ICE) biome is characterised by a generally small magnitude of fluxes into and out of the ocean and a pronounced seasonal cycle with the largest ocean uptake of CO₂ in summer. Connecting these two, the subpolar seasonally stratified (SPSS) biome has intermediate flux magnitude, with GOBMs showing spread in the strength of winter outgassing and difficulties in simulating the strongest CO₂ uptake in summer. The biases in GOBMs originate mainly from the non-thermal component of air-sea CO₂ flux, and in particular from the difficulty in simulating the competing effects of circulation and biology on carbon draw-down in summer. Our analysis reveals a distinct zonal asymmetry (secondary to the latitudinal gradient) between the Atlantic, Pacific and Indian sectors. The zonal asymmetry is observed in the mean uptake and amplitude of the seasonal cycle rather than the phasing of the seasonal cycle. GOBMs show a 20% spread and an overall underestimate of their simulated anthropogenic carbon accumulation, pointing to insufficient water mass formation and interior ventilation. These first results confirm the global relevance of the Southern Ocean carbon sink and highlight the strong regional and interannual variability of the Southern Ocean carbon uptake in connection to physical and biogeochemical processes. 

How to cite: Patara, L., Hauck, J., and Gregor, L. and the RECCAP2 Southern Ocean team: RECCAP2 – Southern Ocean carbon fluxes and storage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17328, https://doi.org/10.5194/egusphere-egu23-17328, 2023.

Here we present a synthesis of surface ocean pCO₂ and air-sea CO₂ flux seasonality for a modern climatology and      their decadal trends between the 1980s and 2010s, as part of the REgional Carbon Cycle Assessment and Processes Phase 2 (RECCAP2) project. Working with both surface ocean pCO₂-observation products (pCO₂ products) and global ocean biogeochemistry models (GOBMs), our main findings are: (i) Over biome scales, both pCO₂ products and GOBMs confirm increases in the seasonal amplitude of pCO₂ and integrated CO₂ fluxes between 1985-1989 and 2014-2018. (ii) For the 2014-2018 climatology, GOBMs exhibit a systematic bias with too-weak biologically-driven seasonal variability in surface dissolved inorganic carbon (DIC), such that the pCO₂ seasonal cycle in subtropical biomes is spuriously large and both the amplitude and phase of seasonal pCO₂ variations diverge from those in the pCO₂ products in subpolar and circumpolar biomes. (iii) Decadal increases in pCO₂ seasonal cycle amplitude in subtropical biomes are attributed to being largely driven by reducing CO₂ buffering capacity and increasing sensitivity to temperature due to increasing anthropogenic carbon (C_ant) content insurface waters for both the pCO₂ products and GOBMs. In subpolar and circumpolar biomes, the seasonality change for GOBMs is dominated by C_ant invasion, whereas for pCO₂ products modulations of the climate state are equally important. (iv) Considered together, the subtropical biomes exhibit decadal increases in CO₂ flux seasonality that are larger during winter than summer, consistent with the mechanism described by Fassbender et al. (2022) and potentially promoting a negative feedback in the climate system by increasing the CO₂ uptake in winter, by virtue of surface winds being stronger in winter than summer. (v) Large ensemble simulations with ESMs were applied to confirm the validity of biomes as aggregation domains for identifying forced signals. Despite compromises to DIC seasonality impacting pCO₂ seasonality, the chosen biome-scale is appropriate for representing the decadal rate of increase of pCO₂ seasonality for both GOBMs  and pCO₂ products.

How to cite: Rodgers, K. and the RECCAP2 coauthors: seasonal variabiltiy in surface ocean carbon cycle: Seasonal variabiltiy of the surface ocean carbon cycle: a global synthesis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10894, https://doi.org/10.5194/egusphere-egu23-10894, 2023.

Around 31% of carbon dioxide derived from human activities (C_anth) has been absorbed by the ocean (DeVries, 2014; Gruber et al., 2019; Sabine et al., 2004). This accumulation helps to mitigate atmospheric carbon dioxide (CO₂), but in turn leads to severe consequences on marine systems (IGBP, IOC, SCOR, 2013). Both components of CO₂, i.e. anthropogenic and natural, present high variability and uncertainties difficult to observe and quantify. In particular, the C_anth signal represents a small fraction of the total dissolved inorganic carbon pool (C_T) and it is not directly distinguishable from the natural component, resulting in the emergence of back-calculation techniques (Brewer 1978; Chen and Millero, 1979) to derive it indirectly. Over the years, back-calculation techniques have undergone remarkable improvements (Gruber et al., 1996; Sabine et al., 2004; Touratier et al., 2004, 2007; Vázquez-Rodríguez et al., 2009a, 2009b, 2012), resulting in different methods for estimating C_anth that, despite providing helpful and advanced results, show various biases and limitations. Here, we present a new approach for estimating C_anth that relies on a back-calculation methodology, purely based on carbon data, and provides results that show good agreement with previous global C_anth climatologies. Our approach mainly differs from previous methodologies by pioneering using the transport matrix output from a data‐assimilating ocean circulation inverse model (TMI: Total Matrix Intercomparison; Gebbie and Huybers, 2010) to obtain preformed properties, instead of the historical use of Optimum Multiparameter analysis (OMP). This improvement prevents from the need to use (sub)surface-property linear regressions to estimate preformed alkalinity or air-sea CO₂ disequilibrium, and allows introducing different corrections for denitrification and, as a novelty, oxygen disequilibrium.

How to cite: López-Mozos, M., Pérez, F. F., Carracedo, L. I., Gebbie, G., and Velo, A.: A new approach for estimating anthropogenic carbon relying on an observational back-calculation method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15146, https://doi.org/10.5194/egusphere-egu23-15146, 2023.

This contribution presents a new view of the global carbon cycle which accounts for the land-to-ocean transport of carbon through inland waters, estuaries, tidal wetlands and continental shelf waters—the ‘land-to-ocean aquatic continuum’ (LOAC). We highlight how biogeochemical and ecological processes from land-to-ocean have been perturbed by human interventions, including atmospheric composition change, climate change and land-use change. The extend to which these anthropogenic perturbations have altered regional and global CO₂ budgets and trends along the LOAC are also presented and the knowledge gaps that are key to reduce uncertainties in future assessments of LOAC fluxes are identified. Finally, broader implications regarding the quantification of the terrestrial and open ocean sinks of anthropogenic carbon are briefly discussed 

How to cite: Regnier, P., Resplandy, L., Rosentreter, J., Najjar, R., and Ciais, P.: The land-to-ocean loops of the global carbon cycle: How much do we know about long-term trends and drivers of changes in CO2 fluxes ?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16001, https://doi.org/10.5194/egusphere-egu23-16001, 2023.

Inland waters are important sources of the greenhouse gasses (GHGs) carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) to the atmosphere. While a growing number of global estimates of inland water GHG emissions exists, the integration of inland waters into regional GHG budgets is often hampered by the lack of adequate geo-spatial datasets. Moreover, existing estimates diverge substantially, in part due to persisting uncertainties related to the size and distribution of effective inland water surface areas.  In the framework of the 2^nd phase of the REgional Carbon Cycle Assessment and Processes (RECCAP-2) initiative, we synthesize existing estimates of GHG emissions from streams, rivers, lakes and reservoirs, and homogenize them with regard to underlying global maps of inland water surface areas and the effects of seasonal ice cover. We then produce estimates of inland water GHG emissions for 10 extensive land regions that are used for the regional land budgets of RECCAP2. According to our synthesis, global inland waters emit 5.6 (3.5-9.1) Pg CO₂ yr^-1, 101 (83-135) Tg CH₄ yr^-1 and 326 (254-592) Gg N₂O yr^-1. South American rivers contribute about one third of global inland water CO₂ emissions. North-American and Russian lakes contribute together one third of global inland water CH₄ emissions. Finally, North America alone contributes one fourth of global inland water N₂O emissions.

The global inland water emissions sum up to a global warming potential (GWP) of an equivalent emission of 13.6 (10.0-20.3) and 8.3 (5.8-12.7) Pg CO₂ yr^-1 at a 20- and 100-year horizon, respectively. At 100-year horizon, the contribution of CO₂ dominates the GWP of global inland water GHG emissions, with rivers being the largest emitters. At the 20-year horizon, on the contrary, lakes and rivers are equally important emitters, and the contributions of CH₄ to the GWP of inland water GHG emissions even exceed those of CO₂. Contributions of N₂O to the GWP appear to be less significant at both time horizons. Normalized to the area of the RECCAP-2 land regions, South America and South East Asia show the highest inland water emission rates in terms of GWP, dominated by riverine CO₂ emissions.

How to cite: Lauerwald, R., Allen, G. H., Deemer, B. R., Liu, S., Maavara, T., Raymond, P., Alcott, L., Bastviken, D., Hastie, A., Holgerson, M. A., Johnson, M. S., Lehner, B., Lin, P., Marzadri, A., Ran, L., Tian, H., Yang, X., Yao, Y., and Regnier, P.: Synthesis, homogenisation and regionalisation of inland water greenhouse gas budget estimates for the RECCAP2 initiative, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1333, https://doi.org/10.5194/egusphere-egu23-1333, 2023.