Advances and Future Prospects of Marine Phytoplankton Carbon Removal Research
As the Earth's largest carbon sink, the ocean absorbs 25% of the carbon dioxide generated by human activities annually. Phytoplankton play a crucial role in the marine carbon cycle by sequestering carbon through photosynthesis during their growth. On February 3rd, Ocean Visions released a report titled "Phytoplankton Carbon Solutions: Priority Research Frameworks for Exploring Carbon Dioxide Removal Potential and Informed Decision-Making." This report assesses the progress and practical application of open ocean phytoplankton carbon removal (CDR) methods, identifies key uncertainties and knowledge gaps regarding their effectiveness and safety, and proposes research priorities and key actions to fill these gaps and support future decision-making.¹ Based on this report, this paper reviews the research methods and recent progress in marine phytoplankton carbon removal, summarizing action plans for the next 5-10 years from three levels: strategic direction, specific pathways, and implementation priorities, aiming to provide a reference for subsequent related research.
01 Research Status
Theoretically, ocean-based CDR methods can achieve gigaton-scale removal. Phytoplankton Carbon Solutions (PCS), as a crucial pathway for marine carbon transport (CDR), consolidates and enhances marine carbon sinks by promoting phytoplankton growth and increasing their ability to transport organic carbon to the deep sea. Iron fertilization is a primary method for promoting phytoplankton growth, but its carbon removal costs are highly uncertain (US$25–53,000/ton). Deep-sea carbon transport also faces the challenge of relying on the highly unstable and difficult-to-measure passive output of organic carbon to achieve sustainable CDR. Currently, four methods—observation, natural analogy, modeling, and field trials—play important roles in PCS research.
(I) Observation
Observational systems are a vital component of field trials and a deeper understanding of natural processes. Rapid advancements in observational technologies have significantly enhanced the ability to assess nearshore events, including the output of particulate organic carbon (POC) to the deep sea. This helps reduce uncertainties in biological carbon pump (BCP) estimations and PCS field trials, improves model input data, and enhances model accuracy and precision. For example, the widely used Argo global real-time ocean observation network can monitor and manage marine resources, providing data on carbon cycle, acidification, and color². However, the construction and operation costs of global ocean observation systems are high, and there are still problems such as a lack of effective carbon output measurement capabilities.
(II) Natural Analogy
Natural analogy can indirectly determine the effectiveness of PCS measures by studying similar natural phenomena without implementing PCS interventions, thus avoiding controversy and public opposition. For example, studying natural phenomena such as seasonal phytoplankton proliferation, volcanic ash deposition events, and shallow hydrothermal vents providing nutrients to surface waters can provide references for phytoplankton proliferation, marine material output dynamics, and the assessment of the potential environmental impact of intervention measures. However, natural analogy has regional specificity, and its research results may not be applicable to areas with different marine biological or chemical conditions, and it also has limitations in deep-sea research.
(III) Models
Models can be used to predict and parameterize CDR potential, estimate environmental risks, and design and analyze field experiments. With the advancement of computing power and artificial intelligence technologies, PCS models can also serve as a cost-effective method for estimating nearshore and deep-sea biological, chemical, and physical dynamics. However, due to the spatiotemporal complexity of marine biological, chemical, and physical factors, relevant models still have shortcomings, such as a lack of ecosystem input data, making it impossible to effectively assess biological effects under nearshore and offshore conditions.
(IV) Field
Experiments Field experiments are semi-controllable and targeted. Well-designed and rigorously executed marine experiments can address issues such as baseline conditions, additional considerations, and environmental impacts for implementing PCS under real and complex conditions, while also providing proof of concept and a basis for standard setting. Zhejiang University's first "Artificial Upwelling Enhancement Demonstration Project" covers an area of approximately 500 mu (0.33 square kilometers) and can increase the surface nutrient concentration³ of at least 5,000 mu of sea area. However, field experiments also suffer from regional specificity, leading to limitations in experimental results due to local oceanographic, biological, and chemical conditions, and involving issues such as high deployment costs, complex permitting procedures, and public participation.
02 Research Progress
In recent years, research on marine phytoplankton carbon removal has made significant progress in areas such as research program deployment, model construction and optimization, monitoring, reporting and verification (MRV), and field experiments.
(I) Research Plans
Research plans and actions facilitate the transition of marine carbon emission reduction (CDR) from theory to practice. In January 2024, the Norwegian Research Council launched the "Reconstruction of Biogenic Carbon Pumps Using Ancient Plankton DNA" (BIOCAP) project, aiming to study marine plankton communities over the past millennia and their role in carbon emissions, thereby gaining a deeper understanding of how climate change affects the efficiency of biogenic carbon pumps (BCPs).⁴ In November 2025, the Ocean Negative Emissions International Big Science Initiative (ONCE) released the "ONCE Integrated Report: From Science to Governance," proposing and systematically explaining the "BCMS four-pump integration" carbon storage mechanism, including BCPs, Carbonate Counter Pumps (CCPs), Microbial Carbon Pumps (MCPs), and Solubility Carbon Pumps (SCPs), constructing a systematic framework from theoretical innovation to governance practice⁵.
(II) Models
Model construction and optimization are important means of conducting PCS research. In January 2024, the Second Institute of Oceanography of the Ministry of Natural Resources and the Italian National Research Council collaborated to improve the light adaptation model for obtaining a complete global map of non-algal particulate matter, capable of describing phytoplankton carbon content in both spatial and temporal dimensions. The improved model acquires non-algal particulate matter data more closely than traditional methods, with the retrieved phytoplankton carbon content showing a relative error of only 7%⁶ compared to field data. In July 2025, a team from the University of Strathclyde, UK, and other institutions constructed Phytoplankton Individual-Based Models (PIBM) based on Lagrange modules simulating phytoplankton communities and Eulerian modules tracking other markers. This model can reproduce the general seasonal patterns of nutrients, chlorophyll, and primary productivity in subtropical oceans, simulating changes in phytoplankton characteristics and functional diversity⁷.
(III) Monitoring, Reporting, and Verification
Reducing the uncertainty of monitoring, reporting, and verification (MRV) is crucial for conducting PCS research. In June 2023, the European Union launched the "Ocean Carbon Dioxide Removal Assessment Strategy" (SEAO2-CDR), aiming to develop a reliable MRV mechanism using Earth system models and autonomous sensors to assess whether ocean CDR technology can serve as an effective method for removing carbon dioxide from the atmosphere⁸. In November 2025, the US non-profit research organization [C]Worthy⁹ announced a new round of funding from the Ocean Resilience and Climate Alliance and the Patrick J. McGovern Foundation to develop an open-source MRV modeling tool for ocean CDR, promoting quantifiable, transparent, and reliable ocean climate solutions¹⁰.
(IV) Field Trials
Conducting field trials is the primary task of PCS research. In April 2024, the US Ocean Vision Center and the Environmental Systems Institute collaborated to develop the first Ocean Iron Fertilization (OIF) Site Suitability Planning Tool, providing multi-dimensional and comprehensive field trial maps for stakeholders in research, planning, resource management, and decision-making, helping to select the most feasible trial deployment sites¹¹. In September 2024, the Exploring Ocean Iron Solution (ExOIS)¹² research organization launched a study on the potential carbon removal capacity of Oceanic Injection (OIF)¹³, involving five aspects: field surveys in the Northeast Pacific, model improvements through field studies, MRV system upgrades, trials of new iron sources and delivery methods, and social science and public governance. This study confirmed that OIF can serve as an effective marine carbon removal (CDR) technology. ExOIS plans to conduct a field trial covering approximately 10,000 square kilometers in 2026¹⁴. In February 2026, researchers from institutions including the Woods Hole Oceanographic Institution called for the initiation of a next-generation OIF field trial, suggesting a 3-6 month study covering approximately 1,000 square kilometers in the Gulf of Alaska in the northeastern North Pacific. This study would comprehensively observe processes such as phytoplankton proliferation, decay, and carbon transport, and record the potential impacts of the field trial on the ecosystem¹⁵.
03 Future Research Focus
In the next 5-10 years, carbon removal research using PCS can be advanced and deployed at three levels: strategic direction, specific pathways, and implementation priorities¹⁶.
(I) Strategic Direction
Address common challenges in implementing PCS and provide a framework and background information for specific pathway research. ① Reduce uncertainty in the net carbon dioxide removal process: Identify the sources of uncertainty for each priority PCS pathway and their impact on CDR, define uncertainty reduction targets, and conduct research to achieve these targets. ② Improve the usability of marine biogeochemical models: Initiate model optimization programs, including model comparison and scenario development, model data input improvement, model innovation potential assessment, and the use of artificial intelligence. ③ Enhance understanding of marine biocarbon pumps: Gain empirical knowledge from ongoing biocarbon pump research and assess PCS interventions based on marine health conditions under normal emission scenarios. ④ Identify and advance high-impact field trials: Use a competitive process to determine field trial designs and proposals, prioritizing funding for trials that produce universally applicable results, meet specific phase review criteria, effectively address regulatory processes, and incorporate social participation in the planning and execution of field trials.
(II) Specific Pathways
Directly investigate specific PCS pathways to understand the environmental and socioeconomic risks involved and potential synergistic benefits. ① Deepen understanding of the scalability potential of Southern Ocean iron fertilization: Conduct feasible scale analyses and scenario simulations to more accurately quantify CDR potential and provide a basis for ecological impact assessment of Southern Ocean iron fertilization. ② Enhance understanding of subtropical nitrogen-fixing iron fertilization: Assess the feasibility and benefits of subtropical nitrogen-fixing iron fertilization through laboratory, model, and field studies. ③ Innovative work on promoting phytoplankton carbon transport: Identify and fund early development, innovation, and testing projects aimed at promoting carbon transport, and select methods for further development based on preliminary results. ④ Continuously monitor and evaluate other emerging PCS pathways: Regularly assess the progress of emerging pathways, prepare subsequent funding support, and use a phased approach to evaluate the merits and feasibility of pathways and investments.
(III) Implementation
Focus Emphasis should be placed on integrating PCS research findings into the discussion and dissemination of climate change and its response solutions. ① Prioritize the role of community participation in research considerations and design: Communicate and collaborate with local communities and other potentially affected groups based on best practices and phased approval processes. ② Targeted capacity building in affected coastal communities and fisheries sectors: Enhance the capacity of fisheries sectors and coastal communities surrounding the PCS project to participate in research, development, and demonstration as early and effectively as possible. Support the development of relevant tools and mechanisms to deepen the understanding of the risks and shared benefits of PCS among fisheries sectors and coastal communities, while providing modeling mechanisms and best practices for community participation and co-design of region-based research. ③ Ensure assessment of PCS impacts under alternative scenarios and no-action scenarios: Support the development, adoption, and promotion of comparative risk assessment frameworks for marine CDRs, CDRs, and other climate solutions. ④ Establish a dedicated PCS research, development, and demonstration program: Promote the deployment of relevant action plans and ensure coordinated, integrated, and inclusive decision-making processes.
Reference:
[1] Ocean Visions. Phytoplankton Carbon Solutions: A Prioritized Research Framework to Investigate Carbon Dioxide Removal Potential and Inform Decision Making. https://oceanvisions.org/phytoplankton-report/
[2] Argo. Science Highlights. https://argo.ucsd.edu/science/science-highlights/
[3] Zhejiang University. The College of Oceanography has built my country's first "Artificial Upwelling Demonstration Project".https://www.zju.edu.cn/2020/0312/c32861a1968266/page.htm
[4] NORCE. Reconstructing the Biological Carbon Pump with Ancient Plankton DNA (BIOCAP). https://www.norceresearch.no/en/projects/reconstructing-the-biological-carbon-pump-with-ancient-plankton-dna-biocap
[5] Xiamen University. China Daily website: The International Big Science Project on Negative Ocean Emissions released multiple results at COP30.https://news.xmu.edu.cn/info/1024/511702.htm
[6] JGR Oceans. Global Variability of Phytoplankton Carbon and Non-Algal Particles from Ocean Color Data Based on a Photoacclimation Model. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023JC019922
[7] Geoscientific Model Development. PIBM 1.0: An Individual-Based Model for Simulating Phytoplankton Acclimation, Diversity, and Evolution in the Ocean. https://gmd.copernicus.org/articles/18/4155/2025/gmd-18-4155-2025.pdf
[8] National Oceanography Centre. New EU Project Launched to Evaluate Mechanisms for Using the Ocean to Remove Atmospheric CO2. https://noc.ac.uk/news/new-eu-project-launched-evaluate-mechanisms-using-ocean-remove-atmospheric-co2
[9] [C]Worthy was founded by several oceanographers in the United States and is dedicated to developing safe and effective open-source tools for removing carbon from the ocean, advancing ocean climate solutions through innovative software and basic research.
[10] [C]Worthy. [C]Worthy Secures Multi-Year Support from ORCA and the Patrick J. McGovern Foundation to Scale Open-Source Marine Carbon-Removal Tools. https://www.cworthy.org/news/cworthy-secures-multi-year-support-from-orca-and-the-patrick-j-mcgovern-foundation-to-scale-open-source-marine-carbon-removal-tools
[11] Ocean Visions. Ocean Visions Unveils Ocean Iron Fertilization (OIF) Site Suitability Planning Tool. https://oceanvisions.org/news-oif-planning-tool/
[12] The ExOIS (Extended Ocean Iron Fertilization Program), based at the Woods Hole Oceanographic Institution, aims to explore the impacts of marine iron fertilization on climate and ecology.
[13] Frontiers in Climate. Next Steps for Assessing Ocean Iron Fertilization for Marine Carbon Dioxide Removal. https://www.frontiersin.org/journals/climate/articles/10.3389/fclim.2024.1430957/full
[14] Scientific American. Scientists Will Engineer the Ocean to Absorb More Carbon Dioxide. https://www.scientificamerican.com/article/scientists-will-engineer-the-ocean-to-absorb-more-carbon-dioxide/
[15] Dialogues on Climate Change. The Case for Ocean Iron Fertilization Field Trials. https://journals.sagepub.com/doi/10.1177/29768659261420631
[16] Ocean Visions. Phytoplankton Carbon Solutions: A Prioritized Research Framework to Investigate Carbon Dioxide Removal Potential and Inform Decision Making. https://oceanvisions.org/phytoplankton-report/
Source：https://mp.weixin.qq.com/s/bwMn-CL36bDqtH5Ms1Mocw