Effective carbon dioxide removal (CDR) strategies are urgently needed to reduce risks of climate change. Here we propose a new strategy for Ocean Alkalinity Enhancement that targets the land-to-ocean component of the inorganic carbon cycle: river-based alkalinity and weathering enhancement (RAWE). RAWE adapts freshwater acidification mitigation technology to capture CO₂ through mineral weathering and by increasing rivers’ capacity to retain and transport bicarbonate to long-term storage in the ocean. Field experiments in Nova Scotia rivers demonstrate the proof of concept, and global-scale modelling of RAWE indicates a potential millions of tonnes of CDR per year. Results suggest that RAWE meets CDR criteria, such as scalability, permanence, safety, and ability to simply quantify the CO₂ removed, whilst delivering ecological co-benefits. 

How to cite: Sterling, S., Halfyard, E., and Hart, K.: Addition of Alkalinity to Rivers: a novel strategy for Ocean Alkalinity Enhancement, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16677, https://doi.org/10.5194/egusphere-egu23-16677, 2023.

On geological timescales, continental silicate weathering plays a crucial role regulating Earth’s climate. Accelerating this slow thermostat might be the key to help mitigate present-day global warming and ocean acidification through increased alkalinity generation produced by enhanced marine silicate weathering. Laboratory studies show that benthic dissolution of olivine minerals can stimulate oceanic CO₂ uptake by increasing seafloor alkalinity release. Although enhanced benthic silicate weathering is an attractive solution to both CO₂ problems, until now its efficiency remains unclear. This is because the intrinsic dissolution rate of silicates in the seafloor remains poorly constrained, while also the impact of secondary reactions such as carbonate precipitation and reverse silicate weathering (authigenic clay formation) remains poorly quantified. Thus, we first need to develop a detailed understanding of natural benthic silicate dissolution and the feedbacks on carbon and silicon cycles.

Here, we couple two well-tested diagenetic model set-ups that resolve benthic carbon, redox and pH dynamics (organic matter degradation, re-oxidation of reduced species, equilibria reactions, carbonate dissolution and precipitation) and benthic silicon dynamics (biogenic silica dissolution, and authigenic silica precipitation) in the uppermost sediments. We use this new framework to resolve natural basalt and/or olivine weathering by explicitly accounting for the dissolution of key basalt constituents (basaltic glass, plagioclase, pyroxene, and olivine). We also account for reverse weathering through illite authigenic formation. The newly coupled model captures the observed shifts in porewater pH and carbonate system, and the dynamics of benthic alkalinity production and consumption associated with marine silicate weathering. We assess the impact of benthic redox state and basalt compositions on benthic alkalinity fluxes by performing an extensive sensitive study over the entire plausible parameter and bottom water forcing space. We find complex links between rates of benthic silicate weathering and net alkalinity production. Ultimately, we will apply the new model framework to explore the geological context of Iceland. As such, we will fully constrain natural rates of benthic silicate weathering associated to the substantial inputs of natural basalts to coastal and shelf sediments.

How to cite: Freitas, F. S., van de Velde, S., Hendry, K. R., Meysman, F., and Arndt, S.: Controls on benthic alkalinity fluxes from natural and enhanced silicate weathering in coastal and shelf sediments: new diagenetic model insights, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1259, https://doi.org/10.5194/egusphere-egu23-1259, 2023.

One strategy for lowering atmospheric CO₂ levels is enhanced weathering, which involves dispersing rock powder to accelerate natural weathering. One obvious application area would be seawater. Because weathering is a chemical reaction, it is influenced by environmental properties like temperature and physical properties like the reaction area.

This study looks into the variability in sequestration rates from spreading of olivine at 13 distinct regional coasts around the world, including those with warm and temperate climates. Furthermore, sensitivity analysis was performed with various combinations of influencing parameters (grain size and seawater temperature) to determine the effects of individual parameter combinations. A 100-year simulation was conducted using geochemical thermodynamic equilibrium modeling (PHREEQC).

According to the simulations, over a 100-year period, CO₂ uptake from atmosphere varies significantly between the seas, ranging from 0.13 (Black Sea) to 0.94 (Banda Sea) tonne (t) CO₂ per t of olivine at a grain size of 100 μm. The difference between warm and temperate region’s atmospheric CO₂ uptake is 0.4 t CO₂ per tonne of olivine dissolve in seawater. A subsequent sensitivity study of parameter combinations reveals that the Black Sea can reach 0.8 t CO₂ consumption rates per tonne of olivine if the material was ground to a grain size of 19 μm while the Banda Sea can reach the same amount of consumption rates at a grain size of 150 μm. The study results suggest that there are large differences of enhanced weathering speeds between different regions.

How to cite: Ramasamy, M. and Moosdorf, N.: Regional variations in the potential for CO2 removal through enhanced rock weathering in aquatic environments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1494, https://doi.org/10.5194/egusphere-egu23-1494, 2023.

We evaluated the large-scale alkalinity distribution in 14 CMIP6 models against the observational data set GLODAPv2 and found that most models as well as the multi-model-mean underestimate alkalinity at the surface and in the upper ocean, while overestimating alkalinity in the deeper ocean. The dissection of the global mean alkalinity biases into their contribution from physical processes (preformed alkalinity), remineralization, and carbonate formation and dissolution showed that the bias stemming from the physical redistribution of alkalinity is dominant. However, below the upper few hundred meters the bias from carbonate dissolution can become similarly important as physical biases, while the contribution from remineralization processes is negligible. In light of ongoing and planned projects involving ocean alkalinity enhancements experiments using ESMs, a back-of-the-envelope calculation was conducted with each model’s global mean surface alkalinity and dissolved inorganic carbon (DIC) as input parameters. It was shown that the degree of compensation of DIC and alkalinity biases at the surface matters more than the alkalinity biases themselves for additional CO₂ uptake capacity. The global mean surface alkalinity bias relative to GLODAP ranges from -3.6% to +2.1% with a mean of -1.1%, while for DIC the relative bias ranges from -2.6% to +2.5% with a mean value of -0.6%. Because of this partial compensation, all but two of the here evaluated CMIP6 models overestimate the Revelle factor at the surface and thus overestimate the CO₂-draw-down after an alkalinity addition of 100 µmol kg^-1  by up to 13% and the pH increase by up to 7.2%. This probable overestimate has to be taken into account when reporting on efficiencies of ocean alkalinity enhancement experiments using CMIP6 ESMs.

How to cite: Hinrichs, C., Hauck, J., Völker, C., and Köhler, P.: Alkalinity and Sensitivity to Alkalinity Enhancement in CMIP6 Earth System Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2245, https://doi.org/10.5194/egusphere-egu23-2245, 2023.

Subduction regions play an important role in transferring carbon from the surface to the deep ocean and sequestering it on a multi-decadal to centennial timescale. Hence, we test the hypothesis that a Carbon Dioxide Removal (CDR) method, namely Ocean Alkalinity Enhancement (OAE) based on olivine addition, is more efficient in deep and bottom water formation region in terms of enhancing the ocean CO₂ uptake.

Using an ocean-only setup of the physical-biogeochemical model FESOM2.1-REcoM3, we quantify the responses to the spatially uniform and continuous addition of olivine (alkalinity, silicic acid and iron) over the period of 2030-2100 under the SSP1-2.6 and SSP3-7.0 emission scenarios in a global (3 Pg olivine/yr) and a regional application (0.22 Pg olivine/yr). For the regional case, we deposit olivine in the major deep and bottom water formation areas of the Southern Ocean, in the Labrador Sea and the Norwegian Sea.

Under the SSP1-2.6 (SSP3-7.0) scenarios, CO₂ uptake increases by 1.2 (1.3) Pg C/yr by the end of the 21^st century in the global case, whereas it increases by 0.2 (0.2) Pg C/yr in the regional case. The area of uniform olivine deposition is significantly smaller in the regional case compared to the global case, yet the regional OAE has a 2.3-fold higher CDR potential compared to the global OAE in both emission scenarios. The high CDR potential in the regional case is largely (80%) attributed to enhanced biological activity resulting from nutrient fertilization in the Southern Ocean, while only 20% is due to enhanced alkalinity. However, the nutrient effect decreases over time. Furthermore, nutrient addition promotes small-phytoplankton calcification in global and regional OAE cases, leading to lower surface alkalinity by the end of the century. Interestingly, CDR potential of adding alkalinity only (without nutrients) is also 4% and 6.6% higher in the subduction regions than in global OAE under the SSP1-2.6 and SSP3-7.0 scenarios. Overall, the subduction regions, hence show higher CDR efficiency in both cases (alkalinity+nutrients, only alkalinity addition). This effect is two orders of magnitude larger when nutrients are included as this essentially includes Southern Ocean iron fertilization.

How to cite: Nagwekar, T., Nissen, C., and Hauck, J.: Effects of Ocean Alkalinity Enhancement in deep and bottom water formation regions on the 21st century CO2 uptake under low and high emission pathways., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7154, https://doi.org/10.5194/egusphere-egu23-7154, 2023.

Ocean Alkalinization deliberately modifies the chemistry of the surface ocean to enhance the uptake of atmospheric CO₂. Here, we quantify, using idealized and scenario Earth system model (ESM) simulations, changes in carbon cycle feedbacks and in the seasonal cycle of the surface ocean carbonate system due to ocean alkalinization. We find that both, the sensitivity to changes in atmospheric CO₂ concentration (carbon-concentration feedback) as well as the sensitivity to temperature changes (carbon-climate feedback) are enhanced. While the temperature effect, which decreases ocean carbon uptake, remains small in our model, the carbon-concentration feedback enhances the uptake of carbon due to alkalinization by more than 20% compared to the carbon sequestration that alkalinity addition would facilitate at constant CO₂ levels. This effect depends on the trajectory of atmospheric CO₂ concentration, and leads to an increased loss of carbon from the ocean if net emissions become negative. The seasonal cycle of air-sea CO₂ fluxes is enhanced due to an increased buffer capacity in an alkalinized ocean. The seasonal cycle of H⁺-ion concentration is also enhanced, although it remains smaller than under preindustrial conditions. This, together with an increased seasonal cycle of the aragonite saturation state in some regions, has the potential to adversely affect ecosystem health.

How to cite: Schwinger, J. and Bourgeois, T.: Ocean carbon cycle feedbacks and the seasonal cycle of the carbonate system under ocean alkalinization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13428, https://doi.org/10.5194/egusphere-egu23-13428, 2023.

The efficiency of open ocean alkalinization is estimated for four regions in the Atlantic: the subpolar North Atlantic, the northern subtropics, the equatorial region and the Southern Ocean. Therefore, a simple one-dimensional model is applied. First, observational based surface values of temperature, salinity, alkalinity, mixed layer depth (MLD), air-sea gas exchange velocity and pCO₂ for each region are derived from the ARMOR3D data set (Guinehut et al., 2012) and the surface pCO₂ data product by Landschützer et al. (2020). The model is run for 26 years, using the data from 1994 to 2019. Alkalinity is added to the mixed layer, which leads to enhanced oceanic carbon uptake, depending on the change in pCO₂ and the gas transfer velocity. When the mixed layer shallows, parts of the added substances remain in the deeper layer of the model (below the mixed layer). They can either be exported, or can be entrained into the mixed layer again when it deepens. In this way, the efficiency of alkalinization (mole of absorbed CO₂ per mole of added alkalinity) for the four regions and varying model parameters (alkalinity, pCO₂, gas transfer velocity, mixed layer depth, fraction of exported carbon/alkalinity) is computed. In addition, the cases with permanent and monthly alkalinity supply (repeated every year) are investigated.

Guinehut, S., A.-L. Dhomps, G.Larnicol and P.-Y. Le Traon (2012). High resolution 3-d temperature and salinity fields derived from in-situ and satellite observations, Ocean Sci., 8, 845–857, https://doi.org/10.5194/os-8-845-2012.

Landschützer, P., N. Gruber and D.C.E. Bakker (2020). An observation-based global monthly gridded sea surface pCO₂ and air-sea CO₂ flux product from 1982 onward and its monthly climatology (NCEI Accession 0160558). Version 6.6. NOAA National Centers for Environmental Information. Dataset. [2021-27-09]

How to cite: Steinfeldt, R. and Rhein, M.: Estimating the efficiency of open ocean alkalinization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14592, https://doi.org/10.5194/egusphere-egu23-14592, 2023.

To assess the potential of coastal ocean alkalinity enhancement as a CO₂ removal option for climate change mitigation, the Flexible Ocean and Climate Infrastructure (FOCI) earth system model was used to simulate alkalinity addition at the European coast open to the North Atlantic. FOCI has a global ocean resolution of 0.5° which can be regionally refined to 0.1° with a two-way nesting approach. The model was run in emission driven mode, starting with a linear ramp up from 2025 to 2035, after which alkalinity equivalent of 1Gt Ca(OH)₂ per year was added in both resolution configurations from year 2035 to 2100 along the European coastline in a high and low emission scenario. To assess regional efficacies, the coast was divided into subsections. We illustrate the importance of adequate model resolution for simulating coastal alkalinity deployment, and show how each coastal region has a different CO₂ uptake efficiency that is caused by differences in the regional environmental and hydrodynamic conditions.

How to cite: Mehendale, N., Wey, H., Kemena, T., Keller, D., and Oschlies, A.: Simulating Ocean Alkalinity Enhancement along the European Coast in an Earth System Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15984, https://doi.org/10.5194/egusphere-egu23-15984, 2023.

Removing large volumes of CO₂ from the atmosphere, as well as rapid and deep emission reductions, may be required to meet the goals of the Paris Agreement. This has catalyzed recent attention on carbon dioxide removal (CDR) approaches that can remove more CO₂ from the atmosphere than they emit. The oceans absorb approximately 25% of the CO₂ that is emitted to the atmosphere, which causes acidification and adds to the stress experienced by some shell-forming organisms. A relatively inexpensive process for creating a hydrated calcium carbonate, ikaite, could be used to mimic the effect of natural carbonate weathering. This process uses high pressure CO₂ (~15 bar) in an aqueous reactor to dissolve crushed limestone within minutes. The calcium rich water is passed to a low-pressure reactor (~0.1 bar) that evolves and recycles gaseous CO₂ and forces the precipitation of ikaite over 30 – 80 minutes at temperatures <15°C. Experimental results suggest complete dissolution of ikaite can increase seawater alkalinity and thus potentially ameliorate the effects of ocean acidification. The focus of this study is on material characterisation and geochemical kinetics. In particular, we are using Raman spectroscopy coupled with X-Ray Diffraction for identification of the materials synthetically formed and we are exploring experimentally the precipitation and dissolution kinetics of ikaite and other hydrated carbonate minerals such as amorphous calcium carbonate (ACC). Preliminary results show that ikaite might be a precursor of ACC and synthetic can be stable for days at low temperature (sufficient time to be added to the ocean) and that it dissolves in seawater and stoichiometrically increases alkalinity.

            This technology could be scaled up to have a meaningful impact on climate change, and the costs could be comparable to other CO₂ removal approaches. That is possible within the next 20 to 30 years, particularly as the raw materials are abundant.

How to cite: Bastianini, L., Peterson, K., and Renforth, P.: Novel method of ocean alkalinity enhancement using ikaite and other hydratedcarbonate minerals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17368, https://doi.org/10.5194/egusphere-egu23-17368, 2023.

Glacial rock flour (GRF) is a felsic, silicate sediment that originates below the Greenland Ice Sheet, where the ice abrades basement rocks to a very fine powder. This is then transported by meltwater rivers or subglacial discharge into fjords and coastal waters. Thus, GRF is a naturally occurring component of the oceans around Greenland. The grain size of GRF typically ranges <1 - 100 µm with a median of 2-5 µm. The material behaves colloidally in water and distributions in fjords and coastal waters show that it has a residence time in the surface layer of up to several weeks. Glacial rock flour deposits are voluminous and common along the coast of Greenland and therefore it has the potential to be applied in geoengineering efforts on a global scale. The potential alkalinization from conservative cation release is estimated to be ~5,000 moles of alkalinity produced per ton of dissolved GRF. Additionally, GRF contains silica and phosphate that may contribute with macronutrients for phytoplankton growth together with various trace metals, e.g., iron and manganese. Hence, adding GRF to ocean surface waters has the potential to influence phytoplankton growth and, at the same time, increase alkalinity. However, the physical and chemical cycling of GRF in the water column, its implications for ecosystem services, and the chemical impact on the carbonate system are not well understood.

The first results from incubation experiments with GRF in the field and from controlled laboratory experiments are presented here. Incubation experiments of GRF added to seawater collected in the Canary Current system showed a significant increase in photosynthetic activity during short term (~1 week) incubations. The positive influence from GRF on phytoplankton biomass and photosynthetic activity is also found in incubation experiments with a monoculture of a green planktonic alga and shows that trace metals mobilized within a few weeks have a significant positive effect on phytoplankton growth. Laboratory experiments of the settling rate of GRF show that the residence time is relatively long but also that flocculation of GRF particles, caused by salinity increases, may be an important process to consider in future field studies. Our results show that GRF has significant potential for increasing alkalinity, and that trace metals are mobilized from GRF in seawater, which can stimulate photosynthesis. We propose that GRF has the potential to impact ecosystem structure and increase biological productivity when applied to the ocean.

How to cite: Bendtsen, J., Daugbjerg, N., Vallentin Larsen, K., Dyrberg Dahms, R., Richardson, K., and Rosing, M.: Impact from glacial rock flour on phytoplankton growth and the carbonate system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7285, https://doi.org/10.5194/egusphere-egu23-7285, 2023.

Every year about 10-14 million m³ of sediments are dredged in the Port of Rotterdam (PoR) as part of harbor maintenance.  Approximately 10% of these sediments are stored in a confined disposal facility (CDF) Slufter due to high levels of toxic metals (cadmium, zinc, mercury, lead, etc.) and persistent organic pollutants, whereas over 90% of the sediments that are not contaminated are currently being relocated to the sea. Whilst the majority of these sediments have the potential to be used in nature-based environmental management projects, there are concerns that the oxidation of these sediments will release greenhouse gases and contaminants to the environment.

The idea of spreading ground olivine in terrestrial and coastal environments to capture CO₂ is becoming increasingly popular due to the urgency to combat climate change. This technique (termed artificially enhanced olivine weathering, EOW) capitalizes on the natural process of olivine weathering that encourages gaseous CO₂ to transform into dissolved bicarbonate ions (HCO₃^-).  In addition, the dissolution of olivine increases soil water pH and allows precipitation of secondary minerals (e.g. Fe oxyhydroxides) that can immobilize toxic metals through adsorption and co-precipitation mechanisms. As a result, EOW could be a promising geo-engineering solution for sediment management at PoR and reduce the negative environmental impacts associated with dredging. However, the specific controls on the drawdown of CO₂ and toxic metal dynamics via silicate weathering are not well constrained.

Through laboratory experiments and field trials, we aim to investigate whether the addition of various commercial olivine-rich mineral mixtures (Greensand, Sibelco sand, etc.) can transform the dredged material from the PoR into a sustainable resource. Several bulk sediment and intact core samples, representing the majority of sediment supplied to the Slufter, were collected from the fluvial stretch of the PoR area. Laboratory batch experiments using artificial seawater were conducted for 90 days (at 1 bar and 12^oC) with (1) only fine-grained (10 – 30 μm) Greensand containing ~62 weight-% forsteritic olivine, 2) only fluvial harbor sediment, and 3) mixtures of Greensand and fluvial harbor sediment. Our results show that olivine dissolution caused significant increases in alkalinity, dissolved inorganic carbon (DIC), and seawater-pH. Nickel concentrations in the aqueous phase remained below the environmental standards in most of the experiments and only slightly exceeded the standard value in experiments with the highest solid/liquid ratio. Furthermore, the mobilization of toxic metals like Zn and Mn from the harbor sediment to the solution was limited in the olivine-sediment mixed experiments, most likely due to adsorption with olivine or with precipitated byproducts of olivine dissolution. Scanning Electron Microscopy / Energy Dispersive X-Ray Spectroscopy (SEM/EDS) analysis of the reacted olivine samples shows the presence of Ca carbonates precipitation but no clear evidence of Mg carbonates or secondary Mg silicate phases (in contrast to results from thermodynamic calculations using PHREEQC). ­Overall, these preliminary laboratory findings indicate that EOW applications in PoR are likely to be viable from an environmental geochemical point-of-view, but further testing in long-term experiments and field trials planned in the project will provide a more accurate assessment.

How to cite: Pokharel, R., Wu, G., King, H. E., Kraal, P., Reichart, G.-J., and Griffioen, J.: Two Birds With One Stone: Artificially Enhanced Olivine Weathering for Sediment Management and CO2 Sequestration in the Port of Rotterdam, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10281, https://doi.org/10.5194/egusphere-egu23-10281, 2023.

Climate change continues to have escalating effects worldwide. Multiple solutions are needed, one of which is carbon dioxide removal (CDR), where CO₂ is removed directly from the atmosphere.

One approach to CDR is ocean alkalinity enhancement (OAE), whereby finely ground alkaline minerals are added to the ocean, increasing pH and total alkalinity and enhancing the ocean’s ability to draw down CO₂ from the air. This effect also helps counter ocean acidification, a phenomenon problematic to marine biodiversity and biogeochemistry.

Here a similar process is investigated but using rivers or fjords settings instead of the coasts. Rivers are proposed to be used as conveyors of finely crushed olivine (10-30 μm) mixed in river water. The goal is for the river to have higher alkalinity and pH before entering the chosen ocean region.
In this work, a closed mesoscale laboratory flume is used to study the feasibility of treating three different conditions, river, fjord, or saltwater, with finely crushed olivine, for alksalisation and CO₂ absorption.

During the experiments, we examined weathering of olivine (details on physical and chemical composition and mineralogy needed) in flowing freshwater, brackish water, and saltwater with a flow rate of 1.25 -1.4 m³/s and the solids-to-liquid ratio of 0,00015 kg. Preliminary results indicate that freshwater is an optimal candidate as a conveyor. Furthermore, using rivers as one of the long-term solutions as an output of alkaline and pH-rich water to targeted regions is suitable.

How to cite: Rønning, J., Campbell, J. S., Renforth, P., and Löscher, C.: Enhanced Weathering of Olivine in Rivers for Carbon Dioxide Removal, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11269, https://doi.org/10.5194/egusphere-egu23-11269, 2023.

Global mitigation commitments which aim to limit global warming to less than 2ºC require dramatic and rapid reductions in atmospheric carbon dioxide (CO₂) over the coming century. Carbon Dioxide Removal (CDR) technologies, whereby CO₂ is actively taken out of the atmosphere and “durably” stored terrestrially, geologically or in the ocean could be employed to help reduce or counter-balance CO₂ emissions to meet national net zero and net negative mitigation targets. Weathering processes would naturally draw atmospheric CO₂ down towards pre-industrial levels over hundreds of thousands of years. One such CDR approach involves accelerating the uptake of CO₂ through “enhanced weathering” (EW). CDR through EW of silicate minerals such as olivine or carbonate minerals can be achieved, for example, by spreading pulverized rocks on soils or employing mine tailings in specialized reactors to increase the weathering rate and hence carbon sequestration on decadal timescales. Here, we explore the efficiency of using mining waste to achieve CDR through EW. We exploit the results of a recent study by Bullock et al. (Science of the Total Environment, 2022) which produced one of the first comprehensive assessments of the global and country level suitability of mine tailings, accounting for reaction kinetics, and their potential for CO₂ drawdown. While the overall CDR from EW of mine tailings is relatively modest, such an approach may still help individual countries meet their net zero goals and it is useful to investigate the broader implications of the deployment of this approach. EW leads to the production of alkalinity and bicarbonate ions (through CDR). We use Bullock et al.’s estimates of the annual generation of these quantities over the coming century to force an ocean biogeochemical model to investigate the impact of the release of these constituents into the ocean on atmospheric CO₂ and ocean chemistry under various emission scenarios. In our simulations, alkalinity and dissolved inorganic carbon (DIC) are injected into the Exclusive Economic Zones of each suitable country or region as identified in Bullock et. al (2022). We examine in particular the competing effects of alkalinity (which increases CO₂ solubility) and outgassing of CO₂ (both due to the injection of DIC and reduction of atmospheric CO₂) on CDR and find that the latter can substantially reduce the efficiency of carbon dioxide removal (by as much as 25% in the lowest emission scenario).

How to cite: Weeks, J., Khatiwala, S., Bullock, L., and Yang, A.: Efficiency of carbon dioxide removal by ocean alkalinity enhancement via enhanced weathering of mine tailings, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5878, https://doi.org/10.5194/egusphere-egu23-5878, 2023.