A deep-ocean climate plan wins rare EPA approval, but is sinking plants in the sea the answer? Innovators who are working on ways to pull carbon dioxide out of the atmosphere to fight climate change are having a tough time lately. Their biggest supporter, Microsoft, recently began telling partners (https://www.nytimes.com/2026/04/16/climate/microsoft-carbon-removal.html) that it is pausing its carbon removal purchases (https://heatmap.news/carbon-removal/microsoft-carbon-removal-pause) . To get a sense of how big of a deal this is, look at the numbers: The tech company alone has purchased approximately 80% of the contracted cumulative volume of carbon removals to date (https://www.linkedin.com/pulse/stop-relying-kindness-strangers-carbon-dioxide-removal-wil-burns-zodfc/) . Its retrenchment is viewed as potentially a major blow (https://www.nytimes.com/2026/04/16/climate/microsoft-carbon-removal.html) to the sector.
However, there may be a bright spot for this industry, and it comes from an unexpected source: The U.S. Environmental Protection Agency quietly decided in March (https://www.epa.gov/marine-protection-permitting/mprsa-research-permit-carboniferous-inc-research-project) to grant a research permit under the Marine Protection, Research, and Sanctuaries Act (https://www.epa.gov/enforcement/marine-protection-research-and-sanctuaries-act-mprsa-and-facilities) to a Houston-based carbon removal startup.
The company, Carboniferous (https://www.carboniferous.co/), aims to assess the potential to durably lock up greenhouse gases by harvesting plants that took in carbon dioxide on land and sinking them to the bottom of the ocean. This approach is often called ‘ocean biomass sinking’ or ‘marine anoxic carbon storage’ (https://puro.earth/our-blog/359-the-path-towards-safe-and-effective-carbon-removal-by-marine-anoxic-carbon-storage). Ocean biomass sinking is one of several carbon removal approaches involving the ocean known as ‘marine carbon dioxide removal’ (https://oceanvisions.org/ocean-based-carbon-dioxide-removal/). Other marine approaches include adding alkaline materials to seawater (https://doi.org/10.1016/j.oneear.2020.07.016) to increase carbon uptake, seeding oceans with iron to stimulate phytoplankton growth (https://www.whoi.edu/ocean-learning-hub/ocean-topics/climate-weather/ocean-based-climate-solutions/iron-fertilization/), and farming seaweed to also take up carbon and sink it.
The Intergovernmental Panel on Climate Change calls carbon dioxide removal “unavoidable” if the world hopes to keep rising temperatures and meet Paris climate targets (https://www.ipcc.ch/report/ar6/wg3/resources/spm-headline-statements/). However, is sinking biomass in the ocean the answer? Personally, I think both pros and cons exist. How does ocean biomass sinking work?
Carboniferous plans to carry out its field experiment in the Orca Basin off the coast of Louisiana. The basin is anoxic, meaning devoid of oxygen, and has a higher concentration of salt than most seawater. The EPA permit allows the company to sink 20 burlap sacks containing sugarcane residue and monitoring equipment (https://www.epa.gov/marine-protection-permitting/mprsa-research-permit-carboniferous-inc-research-project) to study what happens. Globally, land vegetation, including trees and crops, stores about 60 billion tons of carbon annually (https://doi.org/10.1186/1750-0680-3-1) — a large portion released back into the atmosphere when decomposed or burned. Ocean biomass sinking aims to store this carbon on the ocean floor in low-oxygen areas where decomposition slows. Anaerobic processes might leave the biomass intact for centuries or millennia, while colder water could slow decay. The concerns include whether this would be effective on scale and risks to ecosystems.
Recent studies estimate ocean biomass storage could store between 0.1–1 gigatons of CO₂ annually (https://drawdown.org/cluster-2025/biomass-carbon-removal-storage) — a significant amount. Humanity may need to remove 7–9 gigatons annually by the middle century and more by 2100 to meet climate goals. A bigger concern is increasing organic matter in deep ocean environments might boost anaerobic bacteria, which produce methane (https://www.bryceenergyservices.com/2024/09/20/carbon/). Proponents argue that the absence of vertical mixing prevents additional methane release, though more research is needed. Ocean biomass storage could also pose environmental and economic risks, such as releasing particulates or altering microbial activities in the ocean mesopelagic zone, which supports millions of species (https://www.frontiersin.org/journals/climate/articles/10.3389/fclim.2023.1169665). Seafloor communities might react negatively to massive biomass, and introducing large amounts could attract species that feed on dead plant material, altering ecosystem interactions.
Other methods exist, such as Israel’s Rewind (https://www.rewind.earth/) experimenting with burying waste plant matter in the Black Sea region (https://www.rewind.earth/projects/project-macs-romania) and underwater sediments in the Mediterranean Sea (https://www.rewind.earth/projects/project-macs-med-sea). Another Israeli company, BlueGreen Water Technologies (https://bluegreenwatertech.com/), uses hydrogen peroxide to kill harmful algae, eliminating blooms and reducing low-oxygen dead zones. While this approach removes harmful algal blooms, it also sequesters carbon, offering benefits in freshwater ecosystems.
The world’s oceans store roughly 50 times more carbon than the atmosphere (https://ocean-climate.org/en/awareness/the-ocean-a-carbon-sink/) and 20 times more than terrestrial forests (https://www.weforum.org/stories/2023/07/carbon-sinks-fight-climate-crisis/) combined. These findings provide compelling evidence for exploring marine carbon removal options. However, as with all marine-based approaches, questions remain unresolved before large-scale deployment. Carboniferous’ research highlights just one piece of this puzzle.
