New research suggests that seaweed farms’ carbon capture could help remove additional carbon dioxide (CO2) from the atmosphere by altering ocean chemistry, allowing seawater to absorb and store more carbon.
Scientists studying seaweed farms’ carbon capture have discovered that large-scale seaweed aquaculture may increase ocean alkalinity, a chemical property that allows seawater to absorb more CO2 from the atmosphere. This previously overlooked mechanism could strengthen the ocean’s role as a natural carbon sink.
Seaweed farms work in a familiar way at first. Like plants on land, seaweed absorbs CO2 during photosynthesis, converting it into organic carbon as the algae grow. However, researchers have now identified an additional process that could make seaweed farms even more important for climate mitigation. In addition to storing carbon in seaweed biomass, seaweed farms’ ocean carbon capture may also alter ocean chemistry in ways that allow seawater to absorb more atmospheric CO2.
The new research shows that seaweed farms can increase ocean alkalinity. Alkalinity refers to the ability of seawater to neutralize acids and store carbon in stable dissolved forms. This chemical shift occurs partly in the sediments beneath seaweed farms. As seaweed grows, it sheds fragments and organic matter that sink to the seabed. Microbes break down this organic material in the sediments. During decomposition, chemical reactions release compounds that increase alkalinity in the surrounding seawater.
Higher alkalinity allows seawater to absorb additional CO2 from the atmosphere and store it in dissolved forms such as bicarbonate. Through this mechanism, seaweed farms’ ocean carbon capture may help strengthen the ocean’s natural carbon storage capacity.
Scientists say this effect has been largely overlooked in previous research on seaweed aquaculture. Most earlier studies focused on the carbon directly contained in seaweed biomass. However, much of that carbon eventually returns to the atmosphere when seaweed decomposes or is consumed by marine organisms. The newly identified alkalinity pathway could allow carbon to remain stored in ocean chemistry for much longer periods.
As a result, seaweed farms’ carbon capture appears to operate through two different mechanisms. One pathway involves biological carbon uptake as seaweed grows, while the second involves chemical changes in seawater that enhance long-term carbon storage.
To understand the potential scale of this process, researchers modeled how expanding seaweed aquaculture might affect global ocean chemistry. Their simulations suggest that the large-scale expansion of seaweed farms could significantly increase ocean alkalinity in certain coastal regions.
Under some expansion scenarios, these chemical changes could enable the removal of tens of millions of tons of CO2 each year. Some estimates suggest that seaweed farms’ carbon capture could remove roughly 57-60 million tons of CO2 annually.
Although that amount remains small compared to global emissions, it could still contribute meaningfully to climate mitigation when combined with other carbon removal strategies.
Seaweed farming is already one of the fastest-growing sectors in global aquaculture. Kelp and other macroalgae are cultivated for food, fertilizers, cosmetics, and industrial products.
The industry is expanding rapidly in countries such as China, Indonesia, South Korea, and Norway. As farms become larger and more widespread, their potential influence on ocean chemistry may also grow.
Beyond climate benefits, seaweed farms provide several ecological advantages. Kelp forests and farming structures create habitat for fish and invertebrates, increasing local biodiversity.
Seaweed also absorbs nutrients such as nitrogen and phosphorus from coastal waters. This can help reduce pollution caused by agricultural runoff and improve water quality in coastal ecosystems.
In some regions, seaweed farms may even help buffer the effects of ocean acidification. By absorbing carbon dioxide during photosynthesis, kelp temporarily reduces CO2 concentrations in surrounding waters.
Studies have shown that shellfish grown near seaweed farms can develop thicker shells due to improved water chemistry. These benefits highlight how seaweed aquaculture can support both marine ecosystems and climate solutions.
However, scientists caution that seaweed farms’ carbon capture is not a complete solution to climate change. The long-term carbon storage potential depends on several factors, including farm size, ocean circulation, sediment chemistry, and the ultimately use of harvested seaweed.
If seaweed is converted into food or products that later decompose, much of the carbon may eventually return to the atmosphere. For seaweed farming to contribute significantly to long-term carbon removal, some carbon must remain locked in the ocean or stored in durable materials.
Researchers also emphasize that more field studies are needed to quantify the effects of alkalinity in real-world environments. Ocean chemistry varies widely between coastal ecosystems, meaning the carbon removal potential could differ from one region to another.
Despite these uncertainties, the findings suggest seaweed farming may provide a previously underestimated climate benefit. Rather than acting only as a biological carbon sink, seaweed farms’ carbon capture may also function as a chemical amplifier of ocean carbon uptake.
As interest in nature-based climate solutions grows, seaweed aquaculture could therefore play a dual role. In addition to producing food and materials, it may also strengthen the ocean’s ability to absorb carbon dioxide from the atmosphere.
