Q&A: Can we capture CO₂ from the ocean?

Seaweed underwater

The removal of greenhouse gases from the atmosphere has been highlighted as a critical component of almost every path to achieving the goals set by the Paris Agreement.

In order to support Norway and Europe’s climate-neutrality ambitions, the project NCS C+ will develop and mature four climate-positive technologies that focus on removing large volumes of carbon dioxide (CO₂) and methane from the atmosphere. These four pathways are:

  1. Converting algae and/or waste bio-resources into hydrogen and/or heat with CCS,
  2. Removing CO2 from the ocean,
  3. Removing CO2 from the air (often referred to as DAC), and
  4. Removing methane from the air.
  • NCS C+ is a part of the broader LINCCS project.

In this interview, Jorunn Skjermo, a research scientist at SINTEF Ocean, shares insights into NCS C+’s research on capturing CO₂ from the ocean.

How can we capture CO₂ from the ocean?

Answer: The CO₂ concentration in the water is in balance or equilibrium with the atmosphere; the more CO₂ in the atmosphere, the more CO₂ will be taken up by the ocean. That’s why there is enough or more than enough CO₂ for the algae to live and photosynthesise. If you are cultivating a large amount of biomass in the seawater, CO₂ from the water will be taken up in this biomass and more CO₂ from the atmosphere will be taken up by the seawater, by the ocean. So that’s the way we are using the seawater or the ocean to remove CO₂ from the atmosphere.

Why is biomass important for capturing CO₂ from the ocean?

Answer: Biomass is important because that is how you capture carbon in a natural way.
You’re using photosynthesis, where the organism, in this case the seaweed, is capturing CO₂ from the water and using the sunlight to build this into biomass. And we can harvest this biomass, and depending on what we do with it, this can ensure that we keep the carbon and that we do not lose it out in the atmosphere again.

For instance, we can make products that ensure that the carbon is stable for a really long time, maybe several hundreds of years.

What biomasses are you researching in this project?

Answer: In the NCS C+ project, we only work with the seaweed biomass. And the reason for that is that the seaweed or the kelp that we are cultivating here is a very fast growing algae. It’s a macroalgae. It gets very large and it can be cultivated. We have the technology for doing that. This means that we can cultivate up very large amounts of biomass, seaweed biomass, that we can harvest and bring to the factories onshore.

The seaweed that we are using here is a kelp species. It’s a sugar kelp and we have a lot of it in Norway from before. This is a species that thrives well here. We have quite cold water and that is something that this algae likes. And we have very long days during the spring and summer, especially during the spring, which means that it can do a lot of photosynthesis and grow very fast. So this is a species that is very well suited for biomass production, which fits our aims in this project very well.

Why is the ocean an interesting pathway for capturing CO₂?

Answer: Well, I think one of the reasons is that it’s very huge; we have access to very large space, large areas there that can be used for carbon removal. And we can also use it for biomass production through the seaweed farming. And when we are doing seaweed farming, we are using the input factors from the ocean: the nutrients, the temperature, the CO₂ that has been dissolved there, the sunlight that we have there. This means that we have a very sustainable way of producing biomass.

What’s also very good about using the ocean for seaweed farming is that we are not using any arable land that could be used for food production. We’re not using fresh water, we’re not using fertilizers or pesticides; there are many resources that we need when we are cultivating on land that we don’t need when we are cultivating in the sea. So this is of course a very good way of producing biomass.

How do seaweed farms work?

Answer: The seaweed farms are hanging in the water, and we can cultivate at quite large depths because the seaweed farms are always in the upper 10 meters anyway, because they have to be where the sunlight is.

So we can cultivate wherever we want. But of course these farms need to be anchored to the bottom. If it’s starting to get many hundreds of meters deep, then it will be very challenging. We’re aiming for maybe 50 to 70 meters or something like that. And then it works quite well. Norway has a really large ocean areas. In fact, we have six times more ocean than we have land area in this country. And Norway has also the world’s second longest coastline after Canada. It’s 100,000 kilometers, which is 2.5 times around the equator. So we have plenty of space and sea to use for these purposes.

What are you investigating in this project?

Answer: In the NCS C+ project, we are basically working on three main topics. One is to scale up the farming technology to make it more efficient and reduce the production costs. Another one is to look at how we can do this in more offshore conditions because then there will be more available space, and we also know that the productivity of the seaweed will be better if we can go further from the coast. And the third thing is that we are looking into where the best sites for seaweed farming are in Norway, so that we can map out where seaweed farming should be done if we are going to do this at a really large scale.

In addition to algae farming, we are also working on direct ocean capture of CO₂ (DOC). This is an engineered technology whereas algae farming is a natural-based technology. It is also an emerging technology, and that’s why we are also building a small test facility for this in this project, so that we can look further into how this technology can contribute.

What are the potential challenges for this type of pathway?

Answer: I think one of the biggest challenges now is upscaling this technology because the farms today are very small and quite labour-intensive. This is something that we need to do something about. We need to get more mechanised and automised solutions so that there’s not so much manual work any longer. And the farms also need to be more robust and easy to operate so that we can have them in more exposed areas than what is the case today.

We also need to look more into the preservation of the biomass. Once it’s fully grown and we can harvest it, we bring it to the shore and the factories, but not everything can be processed at once because this is season related. Everything will be harvested during a few weeks in the spring and summer. And then we need somewhere to store the algae before we process it, and we need ways to preserve it for this. Maybe not as much in this project, but in other projects that SINTEF is running, we are looking into how we can use acids for preservation, and that works quite well.

When we have these farms out in the sea, we see that there’s a lot of organisms that get attracted to these farms. They want to stay there, they want to hide, they find food there. In a way, it acts as an artificial coral reef. It is a place to be for animals and other plants.
It also extracts nutrients from the sea water. And if the farm is really huge, of course, this could have an impact on the primary production of the natural ecosystem there. This is something that we have to have in mind when we are putting out these farms, so that we are putting them at sites where the nutrient supply is really good, so that it doesn’t negatively affect the primary production in the sea. It can also be used to remove nutrients if you have excess of them. For instance, close to salmon farms or other places where you have extra nutrients coming out.

Any last thing you want to share about this project?

Answer: Yeah, I think it’s important to remember that seaweed is used for many applications.
Today, most of it is used for food and feed and biostimulants. But I don’t think there is any contradiction to also using it for bioenergy or carbon removals because this is something that we can do in addition to using it as a food source – especially in Norway where we don’t have a long tradition for eating seaweeds. It shouldn’t be too contradictory to produce this biomass to use it for carbon capture or carbon removals instead of for food.

I think it would be interesting to combine them with offshore wind farms. This is an idea that has been discussed and researched on for some years now. The main idea is that the ocean wind farms are occupying quite large areas in the sea. For instance, fishermen can’t go there. But if we could use this space, this empty space between the windmills for seaweed farming, then we could have a combined use of it, and get both energy and biomass from the same area. This multi-use of ocean space is something I think will be very important in the future because the ocean is already used for so many things, and there are so many stakeholders that are looking for a new space or new areas to use for their businesses.

Explainer video: The Norwegian Continental Shelf: A Driver for Climate-Positive Norway (NCS C+)


Find out more about the other technologies being investigated by NCS C+:

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