1 Introduction
As the Earth’s largest active carbon reservoir, the ocean holds 44 times more carbon than the atmosphere and exchanges carbon on human timescales, taking up 2.9 Pg C yr−1 from the atmosphere (). Marine carbon dioxide removal (mCDR) represents a diverse portfolio of emerging technologies that aim to enhance the ocean’s natural uptake and storage of atmospheric carbon, utilizing biotic and geochemical strategies (; ; ). Biotic methods enhance biological carbon fixation and export through interventions such as ocean nutrient fertilization, artificial upwelling, macroalgae aquaculture, and ecosystem restoration. Geochemical methods rely on non-biologically mediated interventions that manipulate ocean carbonate chemistry—such as Ocean Alkalinity Enhancement (OAE) and Direct Ocean Carbon Capture and Storage (DOCCS—removal of dissolved inorganic carbon (DIC) from seawater)—or physically enhance the sinking of dissolved and particulate carbon (e.g., artificial downwelling). Beyond carbon removal, mCDR is also attractive for possible co-benefits including fisheries and aquaculture enhancement, production of valuable biomass products, valorization of desalination byproducts, and generation of fuels and industrial chemicals ().
Despite rapid scientific progress, most mCDR methods remain at an early stage of development, with substantial gaps related to CDR durability, additionality (carbon removal above and beyond natural uptake), Monitoring, Reporting, and Verification (MRV), scalability, environmental impacts, and governance (; ; ).
2 Overview of publications in this Research Topic
This Research Topic assembles eleven contributions that illustrate the rapid progress in mCDR science, covering OAE, DOCCS, Ocean Iron Fertilization (OIF), and macroalgae cultivation. The Research Topic includes four Perspective articles focusing on the framework for future mCDR development and its associated MRV challenges and seven Original Research articles investigating specific processes, applied approaches, MRV protocol development, assessments of mCDR efficiency and cost, and environment impacts.
2.1 Perspective articles: framing pathways for responsible mCDR
The four Perspective articles collectively articulate a forward-looking framework for responsible and credible mCDR development, emphasizing durability of carbon storage, robust MRV, environmental risk assessment, and governance.
Buesseler et al., representing the Exploring Ocean Iron Solutions (ExOIS) group, outline a coordinated 5-year research roadmap to assess whether OIF can be a safe, effective, and durable mCDR strategy. Central to their framework is the concept of the “centennial tonne,”—carbon isolated from the atmosphere for at least 100 years, and a call for larger and longer field experiments, improved biogeochemical modeling, robust MRV and environmental MRV (eMRV), and early engagement with communities and regulators.
Hooper et al. examine potential marine ecosystem impacts associated with DOCCS, synthesizing evidence from ocean acidification, OAE, and natural analogues. They identify substantial gaps in empirical knowledge regarding organismal responses to low-DIC, high-pH effluents and conclude that large-scale DOCCS deployment is premature without a dedicated environmental impact evidence base.
Martocello et al. assess the scientific and methodological readiness of macroalgae-based mCDR finding high monitoring costs and lack of validated regional circulation models to be key barriers to scalability and certification. They propose a framework for developing scalable macroalgae-based mCDR through leveraging remote sensing and artificial intelligence for cost-effective monitoring, while advocating for increased public investment in the high-quality, long-term field studies necessary to validate these methods.
Finally, Ward et al. focus on the limitations of ocean biogeochemical models in supporting mCDR MRV. They highlight that existing models are inadequate in resolving fine-scale processes and representing key mechanisms underpinning carbon durability. They propose a roadmap for improving mCDR modeling through refined parameterizations, modular technology-specific components, and systematic testing across diverse ocean settings.
2.2 Original research articles: thematic advances and remaining challenges
2.2.1 Value of laboratory studies and fundamental research
Two Original Research articles highlight the importance of controlled laboratory and mesocosm experiments in advancing fundamental understanding of mCDR processes. Shaw et al. compare industrial Mg(OH)2 with material precipitated from seawater-derived brines for OAE applications, demonstrating that lower crystallinity materials derived from seawater dissolve more rapidly and completely, suggesting that OAE performance can be optimized through material synthesis pathways.
Fucich et al. investigate the influence of microbial biology on aqueous hydroxide-based OAE using sterilized and unsterilized mesocosms. While biological activity accelerated CO2 equilibration, it did not significantly alter the total carbon uptake, supporting the use of mesocosm experiments to inform field-scale expectations and MRV strategies.
2.2.2 MRV challenges and the integration of observations and modeling
Four Original Research articles highlight the challenges of detecting, attributing, and verifying mCDR signals in dynamic marine environments. Stewart et al. evaluate commercially available pH and pCO2 sensors for OAE MRV, finding that uncertainty in pH measurements dominates uncertainty in estimated total alkalinity and that even dense sensor networks may underestimate surface pH changes due to rapid plume dilution. Their results underscore the need to pair sensors with biogeochemical models for accurate signal detection.
Savoie et al. report a proof-of-concept field trial of electrochemically generated aqueous alkalinity discharged through a coastal outfall. Strong tidal mixing rapidly diluted the alkalinity signal, requiring near-field plume modeling to guide sensor placement and interpret observations, echoing the conclusions of Stewart et al.
Ho et al. use a high-resolution regional ocean model to examine OAE in the San Francisco Bay Estuary, showing that estuarine circulation can enhance atmospheric CO2 uptake by exporting alkalinity to the open ocean and increasing the effective air-sea exchange area. Their results demonstrate the importance of local hydrodynamics in mCDR site selection and performance assessment.
2.2.3 Environmental impacts, feasibility, and economics
Environmental risk and feasibility are addressed through complementary experimental and analytical approaches. Ringham et al., working in collaboration with indigenous stakeholders from the Lower Elwha Klallam Tribe, evaluate the effects of electrochemically generated alkalinity exposure on juvenile coho salmon under pulse conditions representative of near-field mixing zones. They observe no detectable adverse effects, illustrating how stakeholder-engaged laboratory studies can inform environmental risk assessments.
Ward et al. conduct a techno-economic analysis of a hypothetical large-scale OIF deployment, estimating levelized costs of carbon removal while highlighting large uncertainty driven primarily by poorly characterized oceanographic variables and MRV infrastructure requirements (e.g., research vessels). Their findings emphasize that reducing scientific uncertainty is a critical engineering optimization for cost-effective MRV.
3 Conclusion
The contributions in this Research Topic advance understanding of mCDR mechanisms, MRV challenges, environmental risks, and pathways toward responsible development. Collectively, they highlight both the potential of mCDR and the substantial work required before large-scale implementation can be considered. Future progress will require improved modeling capabilities, tightly integrated observational-modeling frameworks for MRV, rigorous assessment of ecological impacts, demonstration of economic feasibility, and the development of transparent governance and stakeholder engagement processes.
Statements
Author contributions
MF: Writing – original draft. MG-I: Writing – review and editing. XL: Writing – review and editing.
Funding
The author(s) declared that financial support was received for this work and/or its publication. This publication is funded by the Cooperative Institute for Climate, Ocean, and Ecosystem Studies (CICOES) under NOAA Cooperative Agreement NA20OAR4320271. Contribution number 2026-1564.
Acknowledgments
We would like to acknowledge Olivier Sulpis who served as an editor for this Research Topic. XL thanks the support from the CICEOS postdoc fellowship, 2024 – 2025.
Conflict of interest
The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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Summary
Keywords
carbon dioxide removal (CDR), direct ocean carbon capture and storage, macroalgae cultivation, marine carbon dioxide removal (mCDR), measurement reporting and verification, ocean alkalinity enhancement, ocean iron fertilization (OIF)
Citation
Fong MB, García-Ibáñez MI and Li X (2026) Editorial: Environmental engineering perspectives on ocean-based carbon dioxide removal. Front. Environ. Eng. 5:1908453. doi: 10.3389/fenve.2026.1908453
Received
13 June 2026
Revised
13 June 2026
Accepted
16 June 2026
Published
01 July 2026
Volume
5 - 2026
Edited and reviewed by
Christian Kennes, University of A Coruña, Spain
Updates
Copyright
© 2026 Fong, García-Ibáñez and Li.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Michael B. Fong, fong.michael0@gmail.com
Disclaimer
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.