carbon sequestering

Did you know that some seaweeds can remove 3Kg of carbon per square metrE? that's 30 metric tonnes per hectare per annum!

As our planet continues to warm and the ocean acidifies, solving the global carbon problem becomes more critical each day. Keeping temperatures to survivable levels requires reducing emissions while at the same time working aggressively to absorb as much carbon dioxide as possible, using approaches that can nurture natural ecosystems and help vulnerable human communities flourish.

The ocean plays a major role in global carbon processing and storage, but it’s also among the least utilized. Here, we’ll look at the largely unappreciated but potentially powerful role of the ocean and coastal ecosystems to help solve the global climate problem through Carbon Sequestering.

The ocean absorbs enormous amounts of anthropogenic heat and heat-inducing carbon dioxide. From 1994-2007, the ocean removed from the atmosphere a third more than all terrestrial ecosystems (Trees) combined.

Ocean sediments store more than all terrestrial soils. Overall, about half of all historical carbon emissions have been “sequestered” — stored for hundreds or thousands of years — in the deep sea and ocean sediments through physical and geochemical processing, biological uptake, transformation and deep delivery and through nearshore biological activity.

Taken together, the ocean constitutes a massive carbon “sink” that significantly moderates the effects of climate change. But how can we unlock the vast potential of the sea to help achieve planetary decarbonization? And how do we do that using approaches that help sustain natural coastal and marine ecosystems while also helping to nourish vulnerable human communities?

Managing the climate crisis will require more than a rapid cut in carbon emissions in the coming decades. We must also remove some CO2 from the atmosphere and store it long-term. ‘Blue carbon’ refers to the carbon stored in coastal and marine ecosystems. Its focus has largely been on coastal areas such as mangrove swamps, salt marshes and seagrass meadows, given their accessibility and important role not just in mitigating climate change but in protecting coastlines and providing healthy fisheries. 

Blue carbon policy-making has largely focused on coastal areas too. National projects to restore wetlands started in 2016, concentrating on mangroves however, some researchers are looking beyond coastal areas to the blue carbon potential of deeper waters. Recent research shows that marine animals from krill to whales capture carbon and store it in the ocean. A much-discussed research paper, published last year, found that reducing fishing and allowing populations to rebuild would sequester carbon in living biomass and when carcasses fall to the ocean floor.

 Here at Green Ocean Farming we are working with other companies to look at novel ways to reduce ocean carbon such as focusing on “fishery carbon sinks” and “microbial carbon pumps”. What do they mean and how can they store carbon?


What is a ‘carbon sink fishery’?

Following an experiment that fertilised an area of ocean with iron, to sequester CO2 from the atmosphere by promoting the growth of phytoplankton. It was realised that any type of fishery that doesn’t require extra feed inputs could be used to sequester carbon. Seaweeds (macroalgae) and shellfish farming are the easiest options because they rely on photosynthesis and filter feeding, respectively. While the carbon within a harvested product, such as a shellfish, is broken down and re-released into the atmosphere, at least some of it remains sequestered in the ocean.  

In China mariculture of seaweeds and shellfish is equivalent to over 700,000 hectares of forest planting every year. That’s also the equivalent of the area of China’s rainforest protected by its ecological redlines policies. 

The carbon sink fishery idea could also be expanded to fish, cephalopods, crustaceans, and echinoderms such as sea cucumbers, and that fishing could be included too. Using ocean food chains to build a vertical aquaculture system: kelps, scallops and sea cucumbers bred at varying depths, making use of each other’s metabolites, forming an efficient form of carbon sink.

By using Green Ocean Farming's artificial reefs and technology to control fish shoals to keep bred and released fish gathered in one place, with nearby seagrass and kelp beds, this would also increase aquaculture output and blue carbon. 

Are carbon sink fisheries possible?

The fishing industry catches seafood for people to eat, or for use as feed and industrial raw materials. During those processes, organic matter is broken down, with carbon released to the atmosphere as CO2 or methane. So how would carbon sink fisheries store carbon?

Focusing mainly on shellfish and commercially farmed seaweeds, primarily Kelp, Ulva, and some Wracks. Shellfish absorb CO2 to grow shells of calcium carbonate, a process that stores carbon. Seaweeds also absorb carbon as they grow and at the same time release two less tangible forms of carbon, particulate organic carbon (POC) and dissolved organic carbon (DOC). The former ends up in coastal sediment, while the latter is widely dispersed in seawater.

Both can be stored for long periods. This process of absorbing non-organic carbon and releasing organic, stable forms is termed a “biological carbon pump”.

A 2017 a study found that carbon sequestration mechanisms in coastal mariculture found that POC and DOC accounted for the majority of the carbon stored by seaweeds. Even if seaweeds are harvested and utilised, the review found that most of the carbon they sequester remains in the ocean. The key to carbon sink fishing is to increase fish populations.

 What is a ‘microbial carbon pump’?

The microbial carbon pump referred to is a concept that has had a major impact on international understanding of the potential of ocean carbon sequestration and broadened the definition of blue carbon.

 There is about 20 times as much dissolved organic carbon as there is particulate organic carbon in the ocean. Of the DOC, 95% is “recalcitrant”, meaning it can persist in the ocean for 4,000-6,000 years. The remainder is “labile”, which means it is easily broken down by organisms. Recalcitrant DOC represents a vast store of carbon in the ocean, equivalent to all atmospheric carbon. Expanding that store would provide a route to increasing the ocean’s carbon sequestration.

Scientists have long been aware of recalcitrant DOC but were unsure how it was formed. There was speculation it came from seabed seepage of organics, but research ruled that out. Researchers found that it is formed by microorganisms, which transform labile DOC into the recalcitrant form. The process is efficient and the quantities involved are, thanks to the huge numbers of microorganisms in the ocean, jaw-dropping. They termed these mechanisms “microbial carbon pumps”.

 How do we make it work?

Green Ocean Farming propose two ways to consolidate and expand it, both aim to increase the efficiency of microbial carbon pumps by managing eutrophication – an excess of nutrients, in coastal waters. Excessive nutrients cause microbial carbon pumps to slow and emit more greenhouse gases.


The first approach is land–sea integrated pollutants reduction. It tackles nutrient pollution in the ocean by controlling fertiliser use on land and through other measures. The second is to create “artificial upwelling” in aquaculture zones using clean energy to pump eutrophic water from the seabed up to the surface where the nutrients can be consumed by farmed organisms. This would, the theory goes, increase both carbon storage in aquaculture and the efficiency of carbon pumps. An additional benefit would be the steady circulation of excess nutrients, rather than them being stirred up all at once when storms hit, which can cause algal blooms.

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Until now, kelp forests and other seaweeds have received almost no attention in terms of climate change mitigation policy discussions. Even other blue carbon ecosystems (seagrass meadows, tidal marshes, and mangroves) are a relatively new field. Why is seaweed carbon sequestration important?

Increased focus on seaweed sequestration highlights the potential for kelp forest “afforestation” as a novel climate change mitigation strategy. Policy interventions can encourage kelp production and the carbon sequestration it brings. Governments could directly implement kelp reforestation, kelp farms and protection programs, which have substantial benefits for marine ecosystems and can spur dive tourism. Carbon offset standards can develop kelp offset methodologies, inside or outside a government context (compliance or voluntary offset markets, respectively)

A recent study estimated that about 11 percent of total seaweed production may be sequestered, most of it after it sinks down into the deep sea. That might not sound like a lot. But seaweeds are incredibly efficient when it comes to sucking carbon up and using it to grow. Kelp, for example, can shoot up by as much as two feet each day. “It’s a small percent, but it’s a small percent of a very large number,” said Carlos Duarte, a biologist at the King Abdullah University of Science and Technology and one of the study’s authors. The total production by seaweeds is so large that even if just a small fraction is sequestered, it’s “enough to be globally relevant.”All in all, super-powered seaweeds could sequester around 173 million metric tons (190 million tons) of carbon each year, about as much as the annual emissions of the state of New York.

These numbers are just estimates right now. Duarte and his colleagues plan to conduct field research to get hard data on the sequestration potential of sinking seaweed. Sonja Smith, a marine biologist who studies how nutrients move through ocean ecosystems, was surprised to learn that the carbon in seaweed could be getting stored in the deep sea. “We assumed it mostly cycles back,” she said. “So if a lot of deep sea carbon originates from kelp, that would be amazing. ”Because kelp forests and other seaweed habitats sequester carbon, Duarte said, they should be considered for “blue carbon” efforts that aim to protect and restore carbon-rich marine ecosystems.

Alarmingly, between one quarter and one half of coastal plant habitats have been lost over the last 50 years, and rising temperatures are already shifting the boundaries of kelp forests. These findings add one more dimension to the need to protect kelps and seaweed ecosystems, when we lose kelp we don’t only lose habitat that is a significant for many species, but we also lose an important carbon sink. Governments, local authorities and businesses in general should be encouraged to offset their carbon footprint though sponsorship of both seaweed farming or seaweed reefs. In the same way that airline passengers can pay an airline a fee to counter their carbon footprint.

Instead of planting trees which don't have any real effect on carbon capture for the first few years of their life, the investment would be better spent on seaweed, especially the Kelps. Kelp grows considerably faster than any land based plants 30% - 60% faster. Seaweeds starts to absorb carbon from their surrounding immediately and if left in situ will continue to absorb vast amounts throughout its life, reproducing each Autumn to ensure the continual cycle.  

It takes five years for a tree sapling to start to have any positive effect on its environment, it only takes three months for seaweed to start absorbing large amounts of carbon and releasing oxygen into the seas. After five years the seaweed would have absorbed huge amounts a of carbon compared with a sapling and also released thousands of seaweed spores into the seas, which after only twelve months with would repeat the carbon sequestering of its parent 'plant.' That's an awful lot of carbon trapped by seaweed compared to a tree.  

Where kelp is allowed to fully grow and is not used commercially, kelp cultivation efforts should hypothetically be additional, and therefore a credible source of offsets. Managing natural kelp beds, which face numerous existential threats, could also be a credible offset type. Another option is for governments to promote kelp cultivation through efficient economic incentives for the private sector. Kelp has various commercial uses: as a gel (hypercolloid industry), as an energy source, in pharmaceuticals, in fertilisers, and for invertebrate aquaculture (e.g., abalone, shrimp, sea urchins). Tax breaks for kelp cultivation could provide a “discount” to match the unmonetised social good that cultivation brings through carbon sequestration. Unlike terrestrial ecosystems and coastal marine sediments, the deep sea has minimal direct land-uses, such as farms, urbanization, industry, or coastal resorts. As a result, carbon that enters the deep sea is theoretically insulated against the risks of reversals that affect other biological carbon.

At Green Ocean Farming we offer three options for offsetting your carbon footprint.

Firstly, an eco-friendly Seaweed Farm owned and operated by you/or overseen by us. The seaweed is grown for the purpose of further use, whether that is for Bio Fuel, food, animal feed or other use is up to the investor. This method would also offer a financial return to the investor.

Secondly, a similar set up to the first option but leaving the seaweed to continue growing throughout the year, with the dying fronds being processed by nature and ending up in deep water sinks. This method would still need to be managed by you/us. The seaweed would spore and reproduce naturally each year creating other seaweed or Kelp forests in the area as well on the original ropes. A Hectare of Kelp sequesters around15 - 20tonnes of carbon per year.

Thirdly, our Artificial Seaweed Cubes can be places in the water, purely for the purpose of making seaweed habitats for marine life. Once the seaweed on the eco cubes starts to grow, it makes a perfect nursery for other forms of sea life, some of which feed on the seaweed others just use it for protection. In each case, the seaweed will absorb vast amounts of Carbon while it grows. Our Eco-Cubes are permanent and would have a natural life of 6 - 8 years. 

You can offset your carbon footprint or that of friends and family members, or even your business. We also offer the facility to buy Ocean Carbon Bonds as a gift 

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seaweed and carbon figures
seaweed ocean reef cubes

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