This technology update on biomass sinking summarises the latest developments on the Geoengineering Monitor Map, highlighting new trends for civil society and climate justice movements to follow in their efforts to oppose geoengineering globally. This update is Part Three of a four-part series on marine geoengineering, where we cover other technologies like, Ocean Alkalinity Enhancement (OAE), Direct Ocean Capture (DOC), Ocean Fertilisation (OF) and industrial algae production (coming soon!). It was researched and written by Anja Chalmin, and published with the support of the Geoengineering Monitor team.

Critical developments covered in this update:

• Biomass sinking is a marine geoengineering strategy that aims to sequester carbon by deliberately sinking large quantities of marine or terrestrial biomass onto the deep ocean floor, but recent scientific evidence undermines claims that it is effective and safe.
• Environmental and ecological concerns of large-scale deployment include the risk of generating potent greenhouse gases (like methane), spreading invasive species and pollutants, harming deep-sea ecosystems, and disrupting ocean chemistry and food webs.
• Comprehensive environmental impact assessments are not possible due to significant knowledge gaps, and short research periods cannot justify long-term sequestration claims.
• Biomass sinking on a climate-relevant scale would require vast ocean areas for seaweed farming, potentially harming coastal livelihoods and competing for valuable resources currently used for food, feed, fertiliser, and other applications.
• Despite the uncertainties and risks, numerous private companies such as Blusink (UK), Rewind Earth (Israel), Seafields Solutions (UK), Arbon Earth (Sweden), and others are conducting or planning trials, and aiming to commercialise through the sale of carbon credits.
• For-profit company Carboniferous (USA) plans to conduct an open-ocean biomass sinking trial in the Gulf of Mexico starting this autumn, using baled sugarcane bagasse.
• Running Tide (USA) was the largest provider of biomass sinking carbon credits before going bankrupt, highlighting the market's volatility and the lack of proven long-term sequestration.

Biomass sinking is a marine geoengineering approach which aims to sequester carbon by deliberately sinking large quantities of marine and terrestrial biomass onto the deep ocean floor, where proponents claim it will remain over long timescales. It is by far the most popular marine Carbon Dioxide Removal (CDR) strategy in terms of carbon removal credits sold on voluntary carbon markets, with over 400,000 tonnes having been sold to date. Many of the companies trialing biomass sinking technologies intend to commercialise them in order to sell carbon credits. However, only 5% of the credits have been “delivered” so far, and almost all by Running Tide, a company which has since gone bankrupt. 

The marine biomass used in biomass sinking projects ranges from microscopic single-celled species of microalgae to macroalgae species like kelp seaweed. Macroalgae is usually cultivated in the ocean or collected from existing ocean populations, whereas microalgae is cultivated onshore in purpose-built ponds before being transferred to the ocean. In both cases, proponents argue that carbon uptake by micro and macroalgae reduces the concentration of CO₂ in surface waters, thereby enhancing the ocean's ability to absorb atmospheric CO₂. 

Terrestrial biomass such as agricultural residues and wood contains carbon sequestered from the atmosphere, so proponents claim that the ocean serves as a carbon sink when it sinks to the ocean floor. While some terrestrial biomass is transported into the oceans naturally, deploying biomass sinking on a climate-relevant scale would vastly exceed the scale of these natural processes. 

Another claim made by proponents is that sinking biomass in oxygen-depleted deep-sea regions or anoxic zones causes the biomass to decompose particularly slowly, removing carbon from the biological cycle for 1,000 years or more, with minimal impact on the marine environment. However, there is no sound scientific basis for this claim, insufficient knowledge about how deep-sea ecosystems function, and a lack of understanding of the potential impact of introducing large quantities of biomass into these ecosystems. 

Despite this, companies are ignoring these uncertainties and moving ahead with plans to commercialise biomass sinking technologies, risking unforeseeable ecological consequences which could in turn trigger impacts on the livelihoods of fisherfolk and coastal communities. A large number of recent studies have highlighted the wide-range of likely ecological impacts of biomass sinking, and show that large-scale deployment would be likely to:

• Require huge areas of ocean: A. Jueterbock et al. (2025) calculated that even if all the macroalgae currently farmed were to sink into the deep sea, this would account for only 0.005% of global CO₂ emissions, which is 1% of the amount sequestered by the world’s wild kelp forests. Consequently, large additional seaweed farms would need to be established in order to provide the biomass required for large-scale deployment. However, the open ocean's near-surface area generally lacks nutrients such as iron and nitrate, which would limit the potential for large-scale seaweed aquaculture. In another study, B. Arzeno-Soltero et al. (2023) estimated that harvesting one gigaton of seaweed carbon per year would require over one million square kilometers of seaweed farms in the most productive ocean zones, an area equivalent to the size of Egypt. This area would need to be tripled to attain an additional one gigaton per year. Seaweed farms on this scale would impede other ocean uses, such as shipping and fishing, and disrupt the migration paths of marine mammals.
• Waste valuable resources: Seaweed is a valuable commodity, providing food, feed, fertilisers, pharmaceuticals and other non-food applications, as well as a broad range of ecosystem services. Similarly, terrestrial biomass such as crop residues has a wide range of uses, including for fertilisation and erosion control.
• Affect the ozone layer: GESAMP (2025) points out that current natural marine emissions of bromoform and other halomethanes by macroalgae are estimated to be responsible for almost 10% of stratospheric ozone loss, and these gases also contribute to global warming. Scaling up cultivation could therefore adversely affect the ozone layer.
• Generate potent greenhouse gases: The open ocean is a source of methane, with the gas primarily generated through methanogenesis in anoxic zones. If the dumped biomass were to undergo anaerobic metabolic decomposition in these zones, large quantities of methane, a potent greenhouse gas, would be released.
• Spread non-native and invasive species, and pollutants: T. Chopin et al. (2024) argue that ocean currents transport seaweed over considerable distances, potentially leading to the spread of invasive species and genetic contamination.The marine environment can also be polluted by chemicals contained in agricultural and forestry biomass.
• Harm deep-sea ecosystems and biodiversity: Large amounts of biomass can suffocate organisms such as fragile corals, sponges and microbial communities. Many deep-sea species are particularly vulnerable to disturbances, for example, due to their slow growth rates and low fecundity. As many deep-sea species remain undiscovered and new discoveries happen frequently, it is impossible to fully assess the impact on deep-sea biodiversity and ecosystems. The same is true of anoxic zones, which are far from devoid of life.
• Alter ocean chemistry: The biological degradation of organic matter leads to enhanced oxygen consumption in ocean waters, resulting in oxygen loss, which can lead to hypoxia, or even anoxia in oxygen-poor zones, as well as acidification. Cultivating seaweed in open ocean areas outside of its natural environment may therefore alter ocean chemistry and change microbial physiology and ecology, with potentially detrimental effects on biodiversity.
• Affect the marine food web: Sinking large amounts of biomass to the seafloor could alter benthic (seafloor) food webs, for example by altering population interactions due to changes in microalgal populations. On a large scale, cultivating macroalgae could reduce phytoplankton production, the foundation of the marine food web, by competing for nutrients such as nitrogen, as well as reducing the amount of incoming sunlight reaching the ocean.
• Divert attention away from ecosystem restoration: Biomass sinking schemes will divert attention from effective and low-risk ecosystem restoration measures that genuinely sequester “blue carbon”, such as protecting and restoring seagrass meadows and mangroves. For example, it is estimated that seagrass meadows account for 10% of the ocean's annual CO₂ sequestration, despite covering less than 1% of the ocean's surface area. They also provide vital high economic value ecosystem services, including coastal protection and absorbing nutrients from terrestrial runoff. Such ecosystems are proven to enhance marine biodiversity—and support the livelihoods of coastal communities—by providing food and shelter for a wide variety of marine species, sequestering large quantities of CO₂ and oxygenating the ocean. [1] 

The wide range of risks in the scientific literature demonstrate that dumping biomass can cause changes in all layers of the ocean, not only at the seabed, and deployment on a climate-relevant scale would be likely to have a detrimental impact on oceanic ecosystem services on an unknown dimension. Attempts by proponents to market this method of marine geoengineering as a quick, simple and low-risk solution can therefore be accurately described as 'blue-washing'. 

Companies dumping terrestrial biomass into the ocean

Carboniferous, USA: Approval granted for an open-ocean trial in the Gulf of Mexico

Carboniferous is a for-profit company founded in 2021, and headquartered in the USA. It aims to sink agricultural and forestry biomass into anoxic areas of the ocean in order to generate carbon credits. Carboniferous has close links with the University of California, Santa Barbara, where its research is being conducted. According to its website, Carboniferous plans to collect terrestrial biomass and take it to a collection point, shred and/or briquette it, load it onto a barge on the Mississippi River, and then transport it to the the Orca Basin in the Gulf of Mexico, where it will be dumped into the ocean south of Louisiana. 

In 2025, the company applied to the US Environmental Protection Agency (EPA) for a permit to conduct an open ocean trial, which was granted in March 2026. Friends of the Earth USA has since urged the US administration to withdraw the permit. The trial's stated goal is to assess whether biomass sinking can durably sequester carbon. The trial will be conducted from 2026 to 2028, about 270 kilometers off the coast of Louisiana, and will involve dumping 20 tonnes of sugarcane bagasse via a vessel provided by the Louisiana Universities Marine Consortium, which will depart from the Cocodrie port in Louisiana. The biomass will be dried and compressed into briquettes, which will then be bound together with burlap bags, manila rope and bailing twine. Each bale of bagasse will weigh one tonne and will be attached to a steel anchor using steel shackles. The bales and the steel anchors will remain on the seafloor once the research project has concluded. 

On its website, Carboniferous claims that:	None of the claims are truthful:
Sugarcane bagasse is "not needed for food or other uses"	According to Md. A. Mahmud & F. R. Anannya (2021), sugarcane bagasse has many current and potential uses, and its cellulosic fibers have a variety of other applications.
Anoxic basins are "a dead zone for multicellular organisms" with the "right conditions for preservation of plant matter"	Anoxic zones are far from devoid of multicellular organisms and other lifeforms: R. Danovaro, et al. (2010) reported the discovery of three species of phylum Loricifera (small, multicellular animals inhabit seabed sediment in anoxic zones) in 2010. The researchers also describe permanently anoxic systems as being "inhabited by a huge and partly unexplored microbial biodiversity". C. Callieri, et al. (2019) describe an example of a new discovery made in an anoxic zone, and G. G. Saez describes how organisms in anoxic zones "can live there perfectly well without any oxygen" N. Y. Wagner, et al. (2022) discovered "a diverse and well-populated microbial community" in an anoxic zone, as well as various metabolic processes including methanogenesis, sulphur metabolism and nitrogen metabolism. Carboniferous cannot therefore rule out the possibility of there being organisms capable of metabolising sugarcane bagasse on the ocean floor.
They do not introduce “any new or foreign matter into the ocean”, because similar materials are naturally transported into the oceans by rivers; "we are attempting to amplify this natural cycle in a tightly monitored environment."	Carboniferous downplays the quantities of biomass required for climate-relevant biomass sinking and creates the false impression that the associated impacts can be controlled. However, the potential impacts of dumping vast quantities of biomass cannot be confined to a single area of the ocean.

Blusink, UK: Ongoing and planned biomass sinking trials

Blusink was founded in 2021 and is based in the UK. The company has developed and patented the Blusinkie, an apple-sized pebble meant to sink to the ocean floor. The company claims that "the materials that Blusinkies are composed of are widely present in the ocean naturally - meaning we don't have to worry about adding untested material to the ocean environment. Essentially Blusinkies mimic calcite seafloors". However, the company also states that each pebble is made up of 95% "waste material from brick and ceramic factories, agricultural farming and other industrial processes", which surely contradicts the first claim. 

The ingredients are moulded into discs and fired to transform them into a hard, durable material. Blusinkies also contain calcium carbonate, a substance that gives them 'ocean liming properties', meaning that they are expected to increase the alkalinity of the surrounding water. They are also expected to create an artificial habitat for rhodoliths, which are bottom-dwelling coralline algae found in the ocean. Blusink is currently conducting trials in Colombia, the Maldives and Portugal, and the company also plans to deploy Blusinkies in the Red Sea and off the coast of Indonesia.

Rewind Earth, Israel: Planned and ongoing trials in the Black Sea

Rewind Earth Ltd was founded in 2022 and is headquartered in Israel. The company was established with the aim of removing CO₂ from the atmosphere and selling carbon credits by sinking agricultural and forestry ‘residues’ in bodies of water with anoxic zones. Rewind asserts that "in anoxic waters, plants decompose extremely slowly, effectively storing the carbon much longer” and claims that storing plant biomass in anoxic environments “can safely store carbon for thousands of years". However, the trials conducted by Rewind to support their CO₂ storage claims only lasted one year, which is a questionable basis for this assertion. 

The trials were conducted from 2022 to 2023 at three sites: in the Black Sea off the coast of Trabzon in Turkey; Selker Noor, a small lake in Germany; and the Sea of Galilee, a freshwater lake in Israel. During the trials, various types of biomass were dumped and their dry weight was compared at the beginning and end of the trial period. 

In 2023, the company signed a collaboration agreement with the National Institute for Research and Development on Marine Geology and Geo-ecology in Romania. The partners are planning a two-year trial in the Black Sea, 200 kilometers off the coast of Constanța in Romania. The trial application is still pending. 

Another trial involving dumping 20 tonnes of biomass in the Black Sea is currently taking place off the coast of Haifa in Israel. The biomass is buried beneath sediments dredged up during the cleaning of sea beds in ports, rivers and waterways, aiming to create an oxygen-poor environment, and destroying benthic communities in the process. 

In autumn 2025, Rewind announced the launch of a commercial project to store biomass in an underground mine in Tkibuli, Georgia, and in early 2026, the company announced its intention to focus its commercial activities primarily on storing biomass in mines, while continuing to research biomass dumping in anoxic zones in the Black Sea.

Companies dumping marine biomass in the ocean

Seafields Solutions, UK: Expansion plans in the Caribbean and the South Atlantic Gyre

Seafields Solutions Ltd was founded in the UK in 2021. The company aims to cultivate or collect sargassum seaweed, press it into bales and sink the bales into the deep ocean, selling carbon credits based on this process. To enhance sargassum growth, Seafields has proposed using artificial upwelling to transport nutrient-rich water from the ocean depths to the surface via pipes. 

Since 2024, the company has increasingly focused on using sargassum as a source of feedstock for products such as fertiliser, biochar, and biofuels, rather than for sinking. Seafields explains that "The bankruptcy of Running Tide [see below for more information] and Puro.earth’s decision to exclude aquatic biomass from its methodologies highlighted that near-term funding and market appetite for open-ocean carbon sinking are limited." Despite this, the company continues to pursue its goal of dumping large quantities of biomass in the deep sea, and is also considering an approach whereby it would use sargassum to produce fertiliser and then bale and sink the remaining biomass after having recovered its nutrients.

To ensure a constant supply of sargassum, the company has developed the AlgaePonix system, which consists of a floating paddock for year-round cultivation, as well as the SeaClear barrier to intercept algae before it reaches the shore. The company is currently testing sargassum farming and associated equipment off the coast of Mexico and St. Vincent and the Grenadines. In Mexico, Seafields operates a pilot farm in Quintana Roo, a state on Mexico's Yucatán Peninsula. It collaborates with Carbonwave to produce fertiliser and with RubisCO2 to produce biochar. In St. Vincent and the Grenadines, the company has established several test farms, although information regarding their number and size has not been disclosed. 

Seafields' next goal is to establish test farms and subsequently commercial operations in the Caribbean. Ultimately, the company aims to establish a 'Giga Farm' in the South Atlantic Gyre, covering an area of up to 700,000 square kilometers and using pipes to artificially fertilise surface waters. In a 2025 interview, John Auckland, one of Seafields' founders, discussed the scope of the project and its associated costs, including the fact that the pipes must lift water from a depth of 400 metres with a cost ranging from US$ 100,000 to 1,000,000 per pipe. He asks: "Do we need 400,000 of these pipes, or do we need four million to get to a gigaton of CO₂ removal?” These uncertainties suggest that the Giga Farm is not feasible in the near future, if at all. 

Arbon Earth, Sweden: Sinking seaweed in OceanPods and OceanBaskets

Arbon Earth AB was founded in Sweden in 2022 with the aim of sinking biomass to the seabed and selling carbon credits. The company uses a combination of kelp (Saccharina latissima), bamboo and ropes (which it claims are biodegradable) to create floating islands known as OceanPods. The ropes are seeded with seaweed, and the bamboo enables the structure to float. The OceanPods are released into the open ocean, where they are expected to sink to the seabed after several months of seaweed growth. According to the carbon market platforms Scature and ONCRA, the OceanPods are to be deployed in the North Atlantic, along the Antwerp–America shipping route. However, "some might be elsewhere, e.g. in the waters out of Kenya". The deployment timeframe, quantity and manufacturing location of the OceanPods are all kept confidential. 

Arbon Earth states that so far it has conducted tests in the Atlantic and Indian Oceans, including off the coasts of Indonesia and Iceland, as well as in the Caribbean. From 2026 onwards, the company plans to focus on permit applications and beginning OceanPod production. According to ONCRA, 53 OceanPods are required to sequester one tonne of CO₂. 

Arbon Earth has also developed the OceanBaskets concept, where seaweed is cultivated near the coast and, "when mature, the biomass is placed in bamboo baskets and lowered into the deep ocean waters". How the baskets will be lowered has not yet been explained. In 2026, the company published a white paper intending to prove that deep ocean carbon only returns to the atmosphere after millennia. However, this was not achieved given the lack of data presented and failure to address potential risks such as those outlined in this article.

Seaweed Generation, UK: Commercialisation delayed despite multi-decade licence for trials

Seaweed Generation Ltd (SeaGen), founded in 2021 and headquartered in the UK, aims to collect sargassum seaweed in order to sink it in the deep ocean and sell carbon credits. SeaGen has developed AlgaRay, a solar-powered robot vessel which is intended to collect seaweed and submerge it to a depth of 200 meters, where it is compressed by water pressure, crushing its air bladders. After it is released, it is therefore expected to sink to the seabed. According to SeaGen, the seaweed will reach a depth of 1,000 meters in approximately 1.5 hours. However, no evidence for this claim is provided. 

Following the granting of a 49-year licence by the government of Antigua and Barbuda to conduct trials, SeaGen's approach was tested off the coast of the islands in May 2023. No information has yet been released regarding the scale of the tests or their results. Lionel Hurst, Chief of Staff in the Office of the Prime Minister, described the project as "a very expensive undertaking". In the following year, the company announced plans to sink 50,000 tonnes of sargassum, but there is no evidence that this took place and no indication that new trials are planned in the near future.

Phykos, USA: First tests of a robotic seaweed farm in the Pacific Ocean

Phykos PBC, founded in 2020 and based in the US, aims to grow seaweed in order to capture carbon from the ocean's surface layer and then sink the seaweed in the deep ocean. Phykos has developed a solar-powered autonomous robotic vessel the size of a small boat that floats on the ocean's surface. Lines of seaweed are attached underneath and dragged behind the vessel as it navigates out to the open ocean, steered by software to avoid areas such as shipping lanes. According to the company, the vessel has an integrated clipper mechanism to periodically harvest the kelp, as well as a scale to weigh the seaweed after each harvest, in order to calculate the amount of carbon that has been sunk. The company has reported that a prototype vessel has been tested in the Pacific Ocean and, according to the Ocean Vision Launchpad, "Phykos moves from the design engineering phase into early manufacturing".

SOS Carbon, Dominican Republic: Plans to pump seaweed into the deep ocean

Sargassum Ocean Sequestration of Carbon (SOS Carbon) was founded in 2020 and is based in Punta Cana in the Dominican Republic. This Massachusetts Institute of Technology (MIT) spin-off is seeking to commercialise an approach that involves harvesting and sinking free-floating sargassum seaweed before it reaches Caribbean beaches, using the company’s patented Littoral Collection Module (LCM). The module consists of a long, tubular net attached to a hoop that can be connected to small vessels. Once several nets have been filled, they can be transferred to a larger boat, which would then travel to a deep-water area. There, the seaweed would be pumped through a hose to a depth of 150-200 meters, where the water pressure would force it to sink to the seafloor. SOS Carbon intends to sell carbon credits based on this process, and currently uses sargassum as a raw material for manufacturing products such as fertiliser. The processing of seaweed into fertiliser is conducted in cooperation with Origin by Ocean and SOS Carbon’s sister company, SOS Biotech. SOS Carbon states that it collected a total of 16,000 tonnes of sargassum off the coast of Punta Cana from 2021 to 2025, and claims that one LCM can collect up to 10 tonnes of seaweed per hour.

Running Tide Technologies, USA: Company ceases activities despite raising millions of dollars

Running Tide Technologies Inc. was founded in 2017 and headquartered in the US. Despite having raised over US$ 70 million in the six years following its establishment, the company ceased operations due to a lack of demand for its carbon credits. The company's aim was to sink terrestrial and algal biomass into the deep ocean and at the same time increase ocean alkalinity by coating the biomass with calcium carbonate (CaCO₃). The company's approach involved using basketball-shaped buoys made from wood and seeded with seaweed, such as kelp. While the buoys floated on the ocean's surface, it was expected that the seaweed would grow and the alkaline CaCO₃ would dissolve. After around three months, the seaweed was predicted to become too heavy and sink. The company tested this approach in several locations, including off the coast of Iceland. There, they sank CaCO₃-treated wood buoys made from forestry biomass sourced from Canada and Europe. According to press reports, the company dumped 19,000 tonnes of biomass into the sea off the coast of Iceland between 2022 and 2024, but "they did not clean up the material they had dumped in the ocean."

King Tide Carbon, Canada / UK: Cooperation with algae producers

King Tide Carbon PTE Ltd, a wholly owned Canadian subsidiary of a UK wellness company, was founded with the aim of producing algae biomass in order to sell carbon credits. In 2023, the company entered into a joint venture with Springtide Seaweed LLC, a seaweed producer with a 22-hectare farm in Frenchman Bay, Gulf of Maine, USA. The two companies planned to process the harvested seaweed into biochar and/or dispose of it in the deep ocean. Springtide Seaweed would have been responsible for cultivating various species of seaweed, while King Tide Carbon would have been responsible for selling the carbon credits. Though there is no evidence that this collaboration was successful, the King Tide Carbon website states that the company continues to cooperate with algae producers. Currently, King Tide Carbon is focusing on producing a fertiliser consisting of a blend of nutrients, algae, and biochar made from agricultural 'residues', while continuing to pursue the sale of carbon credits. The company has not yet revealed its next steps with regard to deep-sea biomass sinking.

BlueGreen, Israel: Biomass dumping with chemicals that pose a risk to aquatic life

BlueGreen Water Technologies Co. Ltd. (BlueGreen) was founded in 2014 and is headquartered in Israel, with additional offices in the US, South Africa, and China. BlueGreen's aim is to sell carbon credits based on sinking algae biomass in both freshwater and oceanic environments. The company was established to combat toxic algae blooms and has since worked in several freshwater environments. The company sells and deploys algicides—chemicals that eliminate algae—containing active ingredients such as copper sulphate, aluminum sulphate and sodium percarbonate. The latter releases hydrogen peroxide when it comes into contact with water. According to the European Chemicals Agency, hydrogen peroxide "is harmful to aquatic life with long lasting effects." BlueGreen intends to use satellites, drones and modelling to determine the most effective way to use these chemicals to remove CO₂ on a large scale, although there is no evidence that any of these plans have been put in place. As of May 2026, the company had sold 12,000 carbon credits, despite the environmental risks associated with its approach.

Fiora Mara, USA: Plans to sink entire seaweed farms

Fiora Mara was founded in 2024 and is based in the US. This for-profit company plans to cultivate seaweed on biodegradable, floating farms, which will be sunk to the ocean floor once the seaweed has matured, in order to sell carbon credits. According to the company, "Once our seaweed has matured, our sinking mechanism activates and sinks the entire micro-farm with the seaweed to the deep ocean floor." However, it has not yet revealed any details about this sinking mechanism.

Another claim made by Fiora Mara is that the carbon "remains safely stored for over a millennium", though no evidence of this has been provided. The materials tested for the seaweed farms include bamboo and ropes made of hemp and jute, among others. So far, the company has established a small seaweed hatchery and conducted a small-scale open-ocean trial involving a one-square-meter seaweed farm. Fiora Mara claims that a 100-square-meter seaweed farm can capture 66 tonnes of carbon, but does not explain how this figure has been calculated.

Caspian Environmental Consortium, Kazakhstan: Disposal of microalgae in the Caspian Sea

The Caspian Environmental Consortium Ltd was founded in 2023 and is headquartered in Kazakhstan. Its CaspianCDR project involves researching the cultivation of diatom microalgae in shore-based ponds and their subsequent disposal in the Caspian Sea at a rate of up to two million tonnes per year. The company is considering establishing these ponds in the Mangystau region of Kazakhstan, a coastal area in the central-eastern part of the Caspian Sea. The Caspian Environmental Consortium aims to establish a 30-hectare pond system and deliver the first carbon credits by the end of 2026, with plans to expand to 2,000 hectares by 2036.

Butterfly Carbon, Philippines: Sinking seaweed off the coast of the Philippines

Butterfly Carbon was founded in 2021 and is based in the Philippines. The company's objective is to cultivate sargassum seaweed on floating platforms, harvest it, bale it, and sink it "into the ocean floor 1-5 km depth or even greater to sequester carbon greater than 100-1,000 years and beyond". A near-shore sargassum nursery farm would supply the platforms with seaweed seedlings. The seaweed would then be harvested and transported by photovoltaic and biogas-powered ships. Butterfly Carbon is currently in the R&D phase and is seeking investors.

Further reading:

Center for International Environmental Law & Friends of the Earth US (2025) A Gathering Storm: How Marine Geoengineering Threatens All Ocean Basins, https://foe.org/wp-content/uploads/2025/10/A_Gathering_Storm-_How_Marine_Geoengineering_Threatens_All_Ocean_Basins_report.pdf 

J. Kerry & L. Levin (2025) Dumping Biomass in the Ocean Is Not a Climate Solution, https://www.project-syndicate.org/commentary/push-for-ocean-storage-of-biomass-in-the-black-sea-puts-commerce-over-science-by-james-kerry-and-lisa-levin-2025-04

J. Thomas & ETC Group (2023) The seaweed delusion. Industrial seaweed will not cool the climate or save nature, https://www.etcgroup.org/sites/www.etcgroup.org/files/files/algae_report-en-web-20-sept.pdf

Geoengineering Monitor (2024) Dumping biomass in the open ocean is an unproven carbon removal strategy, but that hasn’t stopped companies from selling carbon credits from it, https://www.geoengineeringmonitor.org/marine-geo-biomass-sinking 

Notes

[1]  Selected sources: 

Kerns, K., et al. (2025) Valuation of blue carbon and ecological co-benefits in temperate seagrass meadows in the Atlantic Virginia Coast Reserve. Ecosystem Services, Volume 76, https://doi.org/10.1016/j.ecoser.2025.101779

Sjafri, N. D. M., et al. (2024) Monetary value of ecosystem services in unhealthy seagrass meadows in Indonesia. Ecosystem Services, Volume 70, https://doi.org/10.1016/j.ecoser.2024.101668

Suwandhahannadi, W. K., et al. (2024) Blue carbon storage in a tropical coastal estuary: Insights for conservation priorities. Science of The Total Environment, Volume 906, https://doi.org/10.1016/j.scitotenv.2023.167733

do Amaral Camara Lima, M., et al. (2023) A review of seagrass ecosystem services: providing nature-based solutions for a changing world. Hydrobiologia 850, 2655–2670, https://doi.org/10.1007/s10750-023-05244-0

United States Environmental Protection Agency (2022) EPA Scientists Study the Carbon-Storing Power of Seagrass to Fight Climate Change, https://www.epa.gov/sciencematters/epa-scientists-study-carbon-storing-power-seagrass-fight-climate-change

Costanza, R., et al. (1997) The value of the world's ecosystem services and natural capital. Nature 387, 253–260, https://doi.org/10.1038/387253a0