A look seaweed carbon sequestration as a viable option in nature-based carbon removal
Living in Cape Town for a number of years, and spending countless hours surfing the kelp-laden spots around Sea Point and my beloved Elands Bay up the West Coast, I didn’t always appreciate kelp. It ruined many a wave for me, I got tangled in it far too many times, and it often gave me frights of my life when thick strands surfaced unexpectedly in the icy pulse of the Atlantic Ocean.
But everything changes when you slip beneath the surface.
Spend even a few moments immersed within these towering underwater forests, watching shafts of light fracture through the swaying fronds, and the nuisance transforms into something almost otherworldly.
What once just felt obstructive reveals itself as alive, rhythmic, and deeply beautiful. A hidden ecosystem, dense with life, moving in quiet harmony beneath the waves, silently, ceaselessly pulling carbon from the sea.
Kelp grows up to 60 centimetres per day. That makes it one of the fastest carbon-capturing organisms on Earth, faster than any land plant, faster than any terrestrial forest. This fact creates a promising vision: thousands of kelp forests cultivated across the open ocean, removing hundreds of millions of tonnes of CO₂ from the atmosphere each year.
The science underpinning its climate potential is real and increasingly well-understood. But the question the global climate community is wrestling with right now is whether the industry around it can grow as fast as the seaweed.
Kelp & carbon
To understand why seaweed carbon sequestration has generated such intense interest, you need to start with the ocean itself.
The ocean already does extraordinary climate work. It absorbs roughly 30% of humanity’s annual fossil fuel emissions, a vast, invisible service that we have barely begun to understand, let alone replicate. Kelp and other macroalgae are part of that system, acting as photosynthetic pumps that pull CO₂ dissolved in seawater and convert it into biomass. As kelp draws down dissolved CO₂, more CO₂ diffuses from the atmosphere into the sea to replace it. The effect ripples upward.
What makes kelp particularly interesting from a climate perspective isn’t just that it sequesters carbon, but where that carbon can go. Scientists have identified three distinct pathways. The first, and most climatically significant, is biomass export. When kelp fragments or dies and sinks below 1,000 metres into the deep ocean, it can lock carbon away for centuries, potentially millennia, in what researchers call the biological carbon pump. The second is dissolved organic carbon (DOC) release, where kelp exudes carbon-rich compounds into surrounding water that can also eventually reach the deep ocean. The third is sedimentary burial, where carbon-containing material settles into seafloor sediments.
The numbers generated by these pathways are striking. A landmark study published in Nature Geoscience estimated that macroalgae — kelp chief among them — exports around 173 million tonnes of carbon to the deep ocean every year, making it one of the most underappreciated carbon sinks on the planet.
These are extraordinary figures for a plant most people only encounter as sushi wrapping.
The scale opportunity
Here is where the optimism, the serious, evidence-grounded optimism, lives.
An estimated 48 to 119 million square kilometres of global ocean is considered suitable for seaweed cultivation. To put that in perspective: it’s 24 to 60 times the size of Greenland. The ocean covers 70% of our planet’s surface, and the overwhelming majority of it is currently doing nothing in the way of managed carbon removal. Kelp farming represents, at least theoretically, a lever of extraordinary scale.
The National Academies of Sciences, Engineering, and Medicine has estimated that cultivated seaweed could remove between 100 million and 1 billion tonnes of CO₂ per year at scale. That is, at the upper end, comparable to taking every car in the United States off the road.
Marine biologist Carlos Duarte, one of the field’s leading researchers, has framed what he calls a “seaweed aquaculture imperative”, the argument that cultivating macroalgae at scale is not just possible but necessary if we are serious about nature-based climate solutions. His work, and that of research groups at Cambridge, Stanford, and UCSB, is helping to close the gap between theoretical potential and verifiable practice. A landmark 2025 Cambridge Earth Sciences study described the carbon-capture potential of kelp forests as significantly “undervalued” in global climate accounting.
South Korea is arguably the most advanced example of this thinking at the national policy level. The South Korean government has developed a national kelp carbon framework, integrating cultivation, accounting, and credit issuance, that is being studied as a potential model for other nations.
The ceiling for this sector, if the science and infrastructure catch up with the ambition, is genuinely significant.
Who’s building it
The global landscape of kelp carbon ventures ranges from government-backed research programmes to VC-funded startups to Indigenous community partnerships. Here are five of the most consequential.
Kelp Blue grows and manages large-scale giant kelp (Macrocystis pyrifera) forests, which they harvest to produce ingredients for agriculture, pharmaceuticals, and textiles. Kelp Blue represents what the sector’s boosters most want to see: a commercially viable operation with independently verified carbon outcomes.
Climate Foundation is attempting to solve one of the sector’s fundamental constraints, which is that in many parts of the open ocean, surface waters lack the nutrients that kelp needs. Its Marine Permaculture system works by either bringing cooler, nutrient-rich waters to cultivated seaweed areas, or lowering the seaweed to the cooler, nutrient-rich water below. Besides helping seaweed grow, it has the wonderful side effects of creating habitats for marine creatures and creating income for ocean communities.
If the platform model can be deployed affordably at scale, it opens up vast ocean areas that would otherwise be unsuitable.
Urchinomics comes at the problem from a different angle entirely. Rather than farming kelp directly for carbon, it restores degraded wild kelp forests by commercially harvesting the sea urchins that are devastating them. Urchins, when their natural predators are removed, graze kelp to bare rock, a phenomenon known as “urchin barrens” that has affected coastlines from Norway to California. Urchinomics feeds captured urchins on agricultural waste, fattens them for high-value seafood markets, and in doing so removes the grazing pressure that is preventing natural kelp recovery. The company has issued what it claims are the world’s first voluntary kelp blue carbon credits under this model.
Oceans 2050 (Global) is doing the unglamorous but essential work of building the measurement infrastructure without which none of the above can be properly verified. Founded by ocean conservationist Alexandra Cousteau, the initiative is running carbon measurement protocols across 21 seaweed farms in 13 countries, with the explicit goal of establishing credible MRV, monitoring, reporting and verification, standards for the sector. Without this kind of foundational work, carbon credits from seaweed farming remain essentially unauditable. Oceans 2050 is trying to build the accounting system the whole industry needs.
Cascadia Seaweed (Canada, British Columbia) is one of North America’s most active commercial operators, farming bull kelp and other species on the BC coast in partnership with First Nations communities. It is also an Oceans 2050 partner, contributing data to the global MRV effort. Its model is notable for combining commercial viability with meaningful Indigenous partnership, a consideration that is increasingly central to how responsible blue carbon projects are evaluated.
Other names worth tracking: Ocean Rainforest (Faroe Islands / USA), which received a $4.5 million ARPA-E award for its offshore Macrocystis cultivation platform and works closely with Cambridge researchers; Ostrom Climate Solutions (also BC), which is developing blue carbon credit methodologies using sediment coring; and Seaweed Solutions (Norway), which is focused on industrial-scale cultivation R&D.
The hard questions
Any honest account of seaweed carbon sequestration has to grapple with the fact that the field is still young, the science is still maturing, and some of the loudest early signals have been cautionary ones.
The most fundamental challenge is permanence. Not all kelp that sinks stays sunk. Some decomposes before reaching the deep ocean, releasing the carbon it contains back into the water column. Research published in Nature in early 2026, in-situ deep ocean monitoring of sunk kelp biomass, found rates of degradation that were significantly faster than some sequestration models had assumed. This doesn’t invalidate the approach, but it does complicate the carbon accounting and makes simplistic claims about “permanent sequestration” look premature.
The second challenge is MRV, monitoring, reporting and verification. There are currently no standardised, internationally recognised protocols for seaweed carbon accounting. This creates a significant problem for buyers of carbon credits derived from kelp farming: without agreed methodologies, it is extremely difficult to assess whether a tonne of “removed” carbon actually represents a tonne of removed carbon. The EU, Japan’s JBE programme, and credit registry Isometric are all working on framework development, but the standards do not yet exist at the scale or rigour the market needs.
Third: ecosystem risk. Large-scale offshore kelp cultivation is not without environmental consequence. Dense cultivation could shade phytoplankton, which are themselves significant carbon sequesterers. It could alter local nutrient cycles. And if biomass is sunk at scale, the cumulative effects on deep-sea ecosystems are genuinely unknown. Responsible operators are thinking hard about these questions, but they are not yet answered.
And then there is Running Tide, the cautionary tale the sector cannot quite escape. The best-funded kelp carbon startup in the United States, Running Tide raised significant capital on the promise of sinking kelp biomass for carbon removal. In June 2024, it shut down its kelp operations amid sustained scientific criticism of its methodology and sequestration claims. The WIRED and DNYUZ investigation into what went wrong is essential reading for anyone considering kelp carbon investments. The lesson isn’t that the approach is wrong, it’s that ambition without rigour is not just scientifically invalid, it’s commercially fatal.
These aren’t reasons to dismiss the sector. They are the growing pains of a field learning from its early mistakes, which is exactly what you want to see in a domain that’s asking to be taken seriously.
Kelp me if you can
The case for seaweed carbon sequestration doesn’t rest on any single company, any single study, or any single carbon credit. It rests on the underlying reality that the ocean is the planet’s largest carbon system, that macroalgae have been part of that system for hundreds of millions of years, and that we are only beginning to understand, let alone work with, that potential.
The sector needs better MRV standards. It needs longer-term permanence data. It needs more transparent carbon accounting, more ecologically careful cultivation practices, and more cases like Kelp Blue where third-party verification has actually been achieved. These are solvable problems. The research institutions are engaged. The policy frameworks are developing. The commercial models, though fragile, are beginning to produce real-world data.
The ocean covers 70% of this planet. For most of human history, we’ve extracted from it. The prospect of working with it — carefully, measurably, at scale — to do something about the carbon problem is genuinely one of the more interesting ideas in climate right now.
The seaweed is ready. The question is whether we can build the institutions, standards, and stories to match it.
If your brand is doing work in the blue carbon or ocean economy space and struggling to tell that story compellingly, that’s exactly what we do at Amandla. Get in touch.
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