This week’s publication highlights relate to carbon monitoring, reporting and verification, forestation, ocean alkalinity enhancement and enhanced rock weathering.
Seawater carbonate chemistry based carbon dioxide removal: towards commonly agreed principles for carbon monitoring, reporting, and verification
Abstract
Carbon Dioxide Removal (CDR) from the atmosphere is unavoidable if we are to meet the Paris Agreement’s goal of limiting global warming to 1.5°C, and almost certainly required to limit warming to 2°C. The ocean exchanges carbon dioxide (CO2) with the atmosphere and is a large repository of carbon that could either be partially emptied to allow more CO2 absorption or have its carbon storage capacity enhanced to allow it to remove additional CO2 from the atmosphere. Early-stage techniques exist to utilise the ocean in atmospheric CO2 removal, but typically, the atmospheric CO2 removal these techniques stimulate happens downstream of their activity. Verifying the carbon removal associated with these techniques, while critical when evaluating the approaches and pricing the removal, is challenging. This study briefly reviews the challenges associated with verifying the carbon removal associated with non-biological (abiotic) engineered marine CDR approaches, specifically Ocean Alkalinity Enhancement and Direct Ocean Carbon Capture and Storage, and presents the findings from a workshop held with interested parties spanning industry to government, focused on their collective requirements for the Monitoring, Reporting, and Verification (MRV) of carbon removal. We find that it is possible to agree on a common set of principles for abiotic marine MRV, but identify that delivering this MRV with today’s understanding and technology could be prohibitively expensive. We discuss focal areas to drive down marine MRV costs and highlight the importance of specification of MRV criteria by an ultimate regulator to stimulate investment into the required work. High-quality MRV is important to correctly price any CO2 removal, but we identify that accessibility and transparency in MRV approaches are also key in realising the broader benefits of MRV to society.
Halloran, P. (2025) Seawater carbonate chemistry based carbon dioxide removal: towards commonly agreed principles for carbon monitoring, reporting, and verification 7 Frontiers in Climate.
Read the full paper here: Seawater carbonate chemistry based carbon dioxide removal: towards commonly agreed principles for carbon monitoring, reporting, and verification I Frontiers in Climate.
Mangrove Forestation for CO2 Sequestration, Sustainable Renewable Energy and High-Value Carbons
Abstract
This comprehensive review explores the multifaceted domain of mangrove biomass, focusing on cultivation, characterization, and utilization for carbon sequestration along with sustainable energy and value-added materials production. The ecological significance of mangroves and initiatives to boost their growth are also highlighted. Despite their crucial role in the global carbon cycle, quantifying and characterizing mangrove biomass poses challenges, emphasizing the necessity for advanced analytical techniques, which are addressed. The potential applications of mangrove biomass in biofuels, composite materials, nanoparticles, and adsorbent materials are explored, focusing on biomass gasification as an environmentally friendly process. Hydrothermal liquefaction (HTL) is also discussed for converting diverse biomass feedstocks into liquid biofuels. As a case review, the mangrove forestation initiatives of Bahrain are addressed. Due to land reclamation, the mangrove covering decreased from 328 ha to 48 ha during 1967–2020. The mangroves’ overall carbon storage decreased from 34,932.2 Mg C ha−1 to 5112 Mg C ha−1. Thus, the potential carbon sequestration dropped from 128,200.44 Mg CO2 equivalent ha−1 to 18,761.04 Mg CO2 equivalent ha−1. The Bahraini effort intends to double mangroves by 2035 as part of its ambitious plan to reduce carbon emissions by 50 % by that year, which supports the United Nations’ sustainable development goals.
Hossain, S. et al. (2025) Mangrove Forestation for CO2 Sequestration, Sustainable Renewable Energy and High-Value Carbons 82 (104472) Sustainability Energy Technologies and Assessments.
Read the full paper here: Mangrove Forestation for CO2 Sequestration, Sustainable Renewable Energy and High-Value Carbons I Sustainability Energy Technologies and Assessments.
Ocean Alkalinity Enhancement in an Open-Ocean Ecosystem: Biogeochemical Responses and Carbon Storage Durability
Abstract
Ocean alkalinity enhancement (OAE) is considered for the long-term removal of gigatonnes of carbon dioxide (CO2) from the atmosphere to achieve our climate goals. Little is known, however, about the ecosystem-level changes in biogeochemical functioning that may result from the chemical sequestration of CO2 in seawater and how stable the sequestration is. We studied these two aspects in natural plankton communities under carbonate-based, CO2-equilibrated OAE of up to a doubling of ambient alkalinity (+2400 µeq kg−1, Ωaragonite∼10) in the nutrient-poor North Atlantic. During our month-long mesocosm experiment, the majority of biogeochemical pools, including inorganic nutrients, particulate organic carbon and phosphorus, and biogenic silica, remained unaltered across all OAE levels. Noticeable exceptions were a minor decrease in particulate organic nitrogen and an increase in the carbon-to-nitrogen ratio (C:N) of particulate organic matter in response to OAE. Thus, in our nitrogen-limited system, nitrogen turnover processes appear more susceptible than those of other elements, which could lead to decreased food quality and increased organic carbon storage. However, alkalinity and chemical CO2 sequestration were not stable at all levels of OAE. Two weeks after alkalinity addition, we measured a loss of added alkalinity and of the initially stored CO2 in the mesocosm where alkalinity was highest. The loss rate in this mesocosm accelerated over time and amounted to ∼10 % of stored CO2 within 4 weeks after alkalinity enhancement. Additional tests showed that such secondary precipitation can be initiated by particles acting as precipitation nuclei and that this process can occur even at lower levels of OAE. In conclusion, in scenarios like our study with carbonate-based OAE, where the carbon is already sequestered, the risk of major and sustained impacts on biogeochemical functioning may be low in the nutrient-poor ocean. However, the durability of carbon sequestration using OAE could be constrained by alkalinity loss in supersaturated waters with precipitation nuclei present. Our study provides an evaluation of the ecosystem impacts of an idealised OAE deployment for monitoring, reporting, and verification in an oligotrophic system. Whether biogeochemical functioning is resilient to more technically simple and economically viable approaches that induce stronger water chemistry perturbations remains to be seen.
Paul, A. et al. (2025) Ocean Alkalinity Enhancement in an Open-Ocean Ecosystem: Biogeochemical Responses and Carbon Storage Durability 22 Biogeosciences.
Read the full paper here: Ocean Alkalinity Enhancement in an Open-Ocean Ecosystem: Biogeochemical Responses and Carbon Storage Durability I Biogeosciences.
Balancing Organic and Inorganic Carbon Dynamics in Enhanced Rock Weathering: Implications for Carbon Sequestration
Abstract
Enhanced rock weathering (ERW) is a promising strategy for CO2 removal via promoting inorganic carbon (IC) sequestration. However, knowledge gaps persist regarding its influence on the largest terrestrial carbon pool, soil organic carbon (SOC) and how these effects evolve as weathering progresses. This study investigated how basalt weathering influences soil carbon fluxes and organic matter (OM) turnover. Over a 6th-month incubation, we applied fresh basalt (fine-sized, olivine-rich) and weathered basalt (coarse- and fine-sized, olivine-depleted) to temperate cropland topsoil, incorporating with 13C-labelled straw. Fresh basalt increases soil pH via rapid H+ neutralization during olivine dissolution, releasing soluble Mg2+ and increasing bicarbonate alkalinity. Combined with continuous carbonic acid dissociation for olivine dissolution, they synergistically enhance dissolved inorganic carbon (DIC) accumulation in soil solution and effluent (~0.4%), promoting soil inorganic carbon (SIC) accrual via carbonate precipitation (~4%). However, rising pH concurrently induces significant SOC losses (~17%), resulting in net C losses of ~13%. As basalt weathering progresses (olivine-depleted), slower H+ neutralization and carbonic acid dissociation during less-reactive Ca-bearing mineral dissolution stabilize soil pH, limiting DIC formation. The released Ca2+ prioritizes SIC accrual via Ca-carbonate precipitation (~4%). Meanwhile, higher specific surface area (SSA) and exchangeable Ca2+ enhance retention and stabilization of both native and straw-derived OC, reducing net C losses (~6%). At both weathering stages, over 95% of total C remaining in soils and effluent exists in organic form. Straw inputs acidify soils by releasing additional free H+ during decomposition, competing with carbonic acid for olivine dissolution and reducing bicarbonate alkalinity, which limits the DIC and SIC accrual at both weathering stages. Since soils continuously receive OM input, understanding the balance between these interactive processes is crucial for optimizing long-term carbon sequestration strategies. Therefore, sustaining SOC by minimizing SOC losses should be prioritized for long-term carbon sequestration, besides IC accrual for ERW, particularly as weathering progresses.
Lei, K. et al. (2025) Balancing Organic and Inorganic Carbon Dynamics in Enhanced Rock Weathering: Implications for Carbon Sequestration 31 (4) Global Change Biology.
Read the full paper here: Balancing Organic and Inorganic Carbon Dynamics in Enhanced Rock Weathering: Implications for Carbon Sequestration I Global Change Biology.
Potential Environmental Impacts and Management Strategies for Metal Release during Ocean Alkalinity Enhancement Using Olivine
Abstract
Ocean alkalinity enhancement (OAE) based on enhanced weathering of olivine (EWO) is a promising marine carbon dioxide removal (mCDR) technique. Previous research primarily focuses on the toxicological effects of potentially toxic metals (PTMs) released from olivine. In this Perspective, we explore the overlooked impacts of EWO on environmental media in two scenarios: olivine applied to beaches/shallow continental shelves and offshore dispersion by vessels. We analyze the potential migration pathways of iron and PTMs (e.g., nickel and chromium) after their release, and their interactions with manganese oxides in sediments, potentially causing secondary contamination. Additionally, we propose mitigation strategies to prevent PTM concentrations from exceeding local environmental quality standards, including the use of alkalization equipment to control PTM levels. This Perspective underscores the need for thorough environmental assessments prior to large-scale implementation to ensure the sustainability and efficacy of mCDR efforts.
Zhuang, W. et al. (2025) Potential Environmental Impacts and Management Strategies for Metal Release during Ocean Alkalinity Enhancement Using Olivine 59 (2) Environmental Science & Technology.
Read the full paper here: Potential Environmental Impacts and Management Strategies for Metal Release during Ocean Alkalinity Enhancement Using Olivine I Environmental Science & Technology.