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New green farm plan will use foul-smelling seaweed to capture carbon

New green farm plan will use foul-smelling seaweed to capture carbon


Sargassum is a blight on beaches across the Caribbean – but British entrepreneurs believe it can become a carbon hero

Mexican scientist Marta Garcia examines Sargassum at a laboratory of the Institute of Marine Sciences in Puerto Morelos, Quintana Roo state, Mexico, on May 15, 2019. - Worried about the increase in the arrival of Sargassum at the Caribbean beaches, scientists, hotel owners and government officials are trying to find ways to get rid of it. Tons of this seaweed are upsetting tourists as locals work around the clock to remove them from the beaches. (Photo by RODRIGO ARANGUA / AFP) (Photo credit should read RODRIGO ARANGUA/AFP via Getty Images)
Sargassum is a blight on beaches but could be an effective carbon store (Photo: RODRIGO ARANGUA / AFP via Getty Images)

A team of British entrepreneurs and scientists are hatching a plan to use a foul-smelling seaweed to store carbon deep in the ocean.

Seafields is a British start-up that plans to construct vast farms in the Atlantic ocean, where sargassum seaweed will be grown, harvested, and sunk to the bottom of the ocean floor.

These floating seaweed nurseries will act as carbon farms. The sargassum will suck in carbon while growing, and then the plant will be harvested, baled and sunk to the ocean floor before it has a chance to decompose and release that stored carbon back into the atmosphere.

This is the kind of long-term carbon storage that will prove vital for controlling climate change, believes Dr Mar Fernández-Méndez a marine biologist and scientific advisor to Seafields. Trapped in the baled, sunken sargassum, “we have a lot of carbon that is stored for thousands of years,” she told i.

Sargassum is not a popular plant. As climate change warms ocean waters, the seaweed has invaded huge swathes of the Caribbean coast. It washes up on beaches, covering the white sand in a thick brown carpet that smells of rotting eggs as it breaks down.

The idea that anyone would deliberately grow sargassum is eccentric. But the reasons why it is so unpopular – its vigorous growth rate and arsenic-tinged fronds – are precisely why it could be a good candidate for carbon storage, said Dr Fernández-Méndez.

It needs very little nutrients to grow, and once it has become established it is very difficult to kill off. “You can harvest it or cut it anywhere and it will keep growing,” she said. Meanwhile, the arsenic means it is not a tasty snack for passing sealife, she pointed out, so there is little chance of losing a farm’s crop to passing predators.

Trying to harvest and bale the sargassum already floating through the Atlantic Ocean would be too energy-intensive to be worthwhile, Dr Fernández-Méndez argues.

So Seafields plans to build dedicated farms where heaps of sargassum is concentrated in a single area, making it easier to harvest and bale.

These farms would be located in the swirling currents of the south Atlantic, where sargassum cannot naturally survive, Seafields co-founder John Auckland told i. “It’s essentially an ocean desert. If we can build our farm there, we’re not borrowing from any existing ecosystem. We are creating our own one from scratch.”

Growing the sargassum somewhere it cannot naturally thrive reduces the risk of it escaping and becoming an invasive pest elsewhere in the world. But the downside is farms in these locations will need an artificial feeding system to cultivate the sargassum.

Seafields is designing a system of upwelling pipes to pull nutrients from the ocean depths and disperse them to the young plants floating on the ocean surface. From there, a heat exchanger would keep nutrients circulating near the ocean surface. Testing of this equipment is set to begin off the coast of Cape Verde in spring next year, with a pilot plant potentially up and running near the Ascension Islands by 2023.

So far the venture is entirely funded by £400,000 of personal investment by the firm’s founders, which include internet pioneers Sebastian Stevens and Russell Parsons, alongside scientists and green finance experts.

Once the farms are up and running, the plan is that companies will buy carbon credits to fund Seafields’ work extracting carbon from the atmosphere. The hope is sargassum farms could be removing a gigatonne of carbon dioxide from the atmosphere every year by 2025.

Yet huge technical and scientific uncertainties remain. It is still not clear, for example, what happens to the baled sargassum once it hits the ocean floor. There are fears the bales could damage delicate ocean ecosystems, turning parts of the ocean floor into a carbon dumping ground. Some studies suggest baling and sinking sargassum could be an effective carbon storage solution, but Seafields’ process will need to be formally verified before it can be offered as a carbon credit. Price is another hurdle; Seafields estimates it will need its carbon credits priced at around $50 per tonne to break even, but the current market rate is just $5 per tonne. 


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