Large-scale seaweed cultivation study highlights opportunities and challenges for carbon removal

June 23, 2026 by jwong | News | #macroalgae | #mCDR | #seaweed

Large-scale seaweed cultivation study highlights opportunities and challenges for carbon removal

A new study led by scientists from the National Oceanography Centre (NOC) has highlighted both the potential and the trade-offs of using large-scale macroalgae (seaweed) cultivation to capture carbon and help mitigate climate change.

The global-scale assessment used the NEMO-MEDUSA ocean biogeochemical model to investigate how extensive seaweed farming could influence the global carbon cycle, ocean chemistry and marine ecosystems under a range of cultivation scenarios.

Seaweed cultivation has been proposed as a marine carbon dioxide removal (mCDR) strategy because seaweed absorbs carbon dioxide during growth and could remove carbon from the atmosphere if harvested biomass is transferred to the deep ocean for long-term storage. The study found that large-scale cultivation could significantly increase the transfer of carbon dioxide from the atmosphere into the ocean.

However, the findings showed that only a fraction of this carbon would be ultimately removed. In some scenarios, while ocean carbon uptake increased substantially, only around 27% of the carbon stored in seaweed biomass contributed to long-term removal.

“Our study shows that large-scale macroalgae cultivation has the potential to enhance ocean carbon uptake, but it also demonstrates that the amount of carbon ultimately removed is actually much smaller than the total amount within seaweed biomass. The results highlight both the opportunities and the challenges associated with scaling up this approach,” said Prima Anugerahanti, a Senior Research Scientist at NOC and lead author.

The research also revealed significant ecological impacts. Large-scale seaweed farming reduced available nutrients in surface waters by more than half, leading to sharp declines in phytoplankton, zooplankton, and the wider marine food web.

Co-author Andrew Yool, a Senior Research Scientist at NOC and member of the TerraFIRMA project, added: “The ocean is an interconnected system, so introducing very large-scale seaweed cultivation doesn’t only affect carbon cycling. Our simulations indicate substantial changes to background ocean biogeochemistry, including nutrient distributions, primary production and ecosystem structure, and these would doubtless impact fisheries and natural populations not in our model. Understanding these wider consequences is essential when evaluating any proposed carbon removal method.”

Additional risks were identified when seaweed biomass was harvested and deposited in the deep ocean. In some scenarios, oxygen concentrations on the seafloor fell by more than 20%, with low-oxygen areas expanding substantially.

The results highly depended on cultivation strategies and model assumptions. While more frequent harvesting improved carbon removal efficiency, it also increased the risk of oxygen depletion at depth. Without added iron to support growth, cultivation was sometimes ineffective and could even result in a net release of carbon dioxide.

Co-author Chelsey Baker, a Senior Research Scientist at NOC, said: “Our findings underscore that macroalgae cultivation should not be viewed as a standalone solution to climate change. While it may have a role to play, effective climate mitigation is likely to require a portfolio of carbon dioxide removal approaches, both marine and land based. Most importantly, drastic emissions reductions are fundamental for there to be meaningful mitigation of climate impacts.”

The authors concluded that large-scale macroalgae cultivation alone is unlikely to provide a viable solution for marine carbon dioxide removal. Instead, future climate mitigation efforts will likely require a portfolio of complementary approaches, including other marine carbon dioxide removal techniques such as ocean alkalinity enhancement.

The research was supported by the UK Research and Innovation (UKRI) projects AtlantiS and TerraFIRMA.