Source: Radio New Zealand
Using microalgae to ‘fix’ carbon is one type of marine carbon dioxide removal. RNZ
Explainer – A start-up company wants to carry out marine carbon dioxide removal in New Zealand waters. What is mCDR and why is it controversial?
Earlier this month, a boat chartered by the company Gigablue headed out to sea from Port Chalmers in Dunedin to an area of deep ocean off the Otago coast called the Bounty Trough.
The plan – according to a notice it filed with the Environmental Protection Authority in February – was to lower five circular ‘containment pens’ into the water, grouped around a central ring so the whole thing looked like a five-petalled flower.
The pens would float on the surface, with fine mesh nets hanging under them to contain 55kg of the company’s particles – small balls of cellulose embedded with iron and manganese.
For three weeks, they would drift in the ocean, with water samples taken every so often before the pens and particles were retrieved and taken back to land.
It was a vastly scaled-back version of a trial the company initially wanted to carry out last year, where up to 1000 tonnes of particles would have been put in the water and allowed to sink into the ocean.
Gigablue is one of a number of start-ups and research groups working in the growing field of marine carbon dioxide removal (mCDR).
There are a range of different mCDR methods that have been proposed, but all of them have the same aim – to draw carbon dioxide out of our rapidly warming atmosphere and store it in the deep ocean.
If mCDR can be proven to work at scale, then it could be a vital tool to help cool the planet.
What Gigablue is doing has drawn particular attention, because its approach resembles a controversial type of mCDR called ocean fertilisation.
Gigablue says there are crucial differences that separate its approach from ocean fertilisation.
But experts RNZ spoke to say, regardless of definitions, all mCDR techniques are in their infancy, and their effectiveness and safety are yet to be proven.
Some say it’s also a big distraction from what the world should really be focusing on: cutting the emissions we produce in the first place.
What is ocean fertilisation?
University of Tasmania marine scientist Lennart Bach says all mCDR is “relatively nascent”, gaining traction in the last decade or so.
“There are start-ups that work in this space and the [academic] research is also really kicking off.”
There are a range of different mCDR methods – Bach’s own research focuses on an approach called ocean alkalinity enhancement.
Ocean fertilisation is another major area of investigation, with experiments dating back 20 years or more.
The premise of both ocean fertilisation and Gigablue’s approach, which it calls microalgae carbon sinking and fixation, is based on a natural cycle that already occurs in the ocean where phytoplankton (a type of microalgae) grow and die.
Phytoplankton need light and nutrients to grow.
Just like trees, phytoplankton capture carbon dioxide as they grow, through photosynthesis. Most plankton are eaten, but some fall to the deep ocean as ‘marine snow’ when they die, taking the carbon with them.
Because deep, cold ocean currents take a long time to circulate, the carbon can theoretically stay there for decades, centuries or even millennia before it resurfaces.
As well as light, phytoplankton need nutrients, including iron.
But there are places in the ocean where iron is scarce – including large parts of the Southern Ocean.
Research has shown that if iron is added to the water in these areas, it can trigger phytoplankton growth. More algae equals a greater mass of marine snow, equals more carbon sinking into the deep ocean, and – eventually – less in the atmosphere as the surface ocean absorbs carbon dioxide to replace what’s been sunk.
Does it work – and is it safe?
In theory, ocean fertilisation can sequester extra carbon, Bach says. “We have lots of model studies that can show that.”
In reality, each step in the sequence is exceptionally tricky to measure and prove in reality, he says.
“The problem is that the biology is so complex, there’s so many pathways in which things can go wrong or things can happen unexpectedly.”
Ocean fertilisation takes place in an ‘open system’ – in this case, an unbounded ocean.
James Kerry, a senior marine scientist at European NGO OceanCare and adjunct research fellow at Australia’s James Cook University, says that increases the complexity of observing and measuring any effects – good and bad.
“The ocean is a very dynamic, chaotic system,” he says.
“It is very, very difficult, and we see this with marine CDR in general, to predict how a particle or a substance that you add to the ocean will actually behave.”
OceanCare senior marine scientist and James Cook University adjunct researcher James Kerry Supplied / James Cook University
To show that ocean fertilisation works, three main things have to be measured: efficacy, additionality, and permanence.
Efficacy requires proof that however you choose to encourage phytoplankton growth actually works – whether it’s on a particle or free-floating blooms in the ocean.
Additionality involves showing that more phytoplankton are growing, and storing more carbon, than if you hadn’t done anything.
Something called ‘nutrient robbing’ is a particular problem here. Adding iron, without adding the other nutrients the plankton need, can ‘rob’ those nutrients from another part of the ocean where plankton might have otherwise bloomed naturally, turning the whole premise into a zero-sum game.
There could be large geographical or time differences involved – making it hard to know what may or may not have otherwise happened.
Permanence is being able to show that the carbon absorbed by the phytoplankton is actually stored, and stays stored.
Many things can interrupt this process – including the fact that phytoplankton are at the beginning of marine food chains. If they’re eaten or decompose in shallower waters, then most of the carbon they’ve absorbed will be rapidly recycled back to the surface ocean and atmosphere.
Even for the small proportion of plankton that sink to the deep ocean, long-term sequestration is not guaranteed. In general, the deeper the plankton sink, the longer the carbon is stored, but research has found that even at depths of 1000 metres most of the carbon returns to the surface within decades.
In the meantime, ocean fertilisation also comes with risks.
There’s potential for creating harmful algal blooms, reducing oxygen in deep ocean ecosystems, and affecting marine food chains.
Algal blooms occur when there are large amounts of nutrients available in surface waters. RNZ / Cole Eastham-Farrelly
Helene Muri, a senior scientist at Norwegian climate and environmental research institute NILU, says “much better monitoring” is needed for every single stage of ocean fertilisation and other forms of mCDR.
“Research is still needed on several core questions before specific methods could be considered safe and effective at scale,” she says.
It was hard to distinguish between the effect of something done deliberately and what might have happened naturally anyway, “especially given sparse observations offshore and at depth”.
“Tracking where that carbon goes in the ocean interior, and whether it later resurfaces, is also really challenging.”
What does the law say?
For all these reasons, ocean fertilisation – and marine geoengineering in general – has become a focus for international laws governing the ocean.
New Zealand is among members of something called the London Protocol, which governs marine dumping.
In 2008, London Protocol members agreed that ocean fertilisation is covered by the protocol, and that it should be restricted to “legitimate scientific research”. In 2013 they agreed to an amendment that would heavily regulate all marine geoengineering, with ocean fertilisation the first to be added to a list of techniques.
New Zealand has not ratified the amendment, which remains non-binding, but international convention means New Zealand is expected to still act in line with what it has agreed to.
At home, New Zealand’s own laws governing the exclusive economic zone prohibit dumping, and ‘placement of matter’ unless there are specific exclusions.
That includes marine scientific research – which is why Gigablue has been able to carry out some limited ocean trials to date.
However, the larger trials it wanted to do were found to constitute marine dumping by the EPA, which also had concerns about the environmental effects.
As reported by RNZ, Gigablue was last year seeking changes to regulations that would create an exclusion for marine carbon dioxide removal.
What about companies wanting to commercialise?
The London Protocol amendment says that any ocean fertilisation activities should be designed to answer questions that add to scientific knowledge.
“There should not be any financial and/or economic gain arising from the experiment,” it states.
This creates problems for any company wanting to get carbon credits issued and verified, if its technology fits within the definition of ocean fertilisation.
James Kerry says he believes that is why Gigablue – which already has a contract to deliver 200,000 carbon credits by 2029 – is keen to distinguish its technology as something else.
“The distinction determines which international rules and safeguards apply to the activity that GigaBlue is proposing to undertake.”
Gigablue, for its part, has said it needs to be able to verify credits in order to fund the research that will provide the evidence base for its technology.
Gigablue has completed three trials in New Zealand waters, including some where particles were released into the water. The most recent trial required them to be contained within ‘pens’. RNZ
Helene Muri says the practice of pre-selling credits for carbon removals is relatively common – especially for proven forms of carbon sequestration like forest planting. However, credits should not be issued before the method is proven, she says.
“If payment helps fund development, but credits are only issued after verified delivery, that can be defensible.”
She, and others RNZ spoke to, support New Zealand ratifying the London Protocol amendment and using its assessment framework to decide which activities can go ahead.
“Fund and permit responsible, open and transparent research to build evidence,” Muri says.
“But resist policies that enable rapid commercialisation until ecological risks are actually bounded and safeguarded, international law compliance is demonstrated, and [monitoring, reporting and verification] is robust.”
Where else is this happening?
Marine carbon dioxide removal research is happening in many other locations, including the US, Canada and Australia, which are considering the same challenges as New Zealand.
A Canadian senate report published last month recommended its government should “create a regulatory framework that enables innovation and balances risks with opportunities”.
However, the report was focused almost entirely on a different type of mCDR that is limited to harbours and rivers, rather than open ocean systems.
James Kerry says the ongoing lack of global regulation has allowed a “broader pattern” of activity to develop, where mCDR approaches are hyped before there’s robust evidence that they work or can be scaled up.
He raises the example of Running Tide, an ocean fertilisation start-up that attracted blue-chip investment from the lies of Microsoft before it closed down in 2024.
“Running Tide dumped around 19,000 tons of matter in Icelandic waters in total in 2023 under a research permit,” he says.
“It’s also worth noting that after Running Tide went bust in 2024, they did not clean up the material they had dumped in the ocean.”
Without careful regulation there was a “real risk” that commercial mCDR activity would move ahead of the science and safety, he says.
He also believes novel tech like marine carbon dioxide removal risks distracting from or delaying actual emissions reductions.
“”You always begin with the narrative, ‘Climate change bad,’ which is true. ‘We need to address the problem,’ which is true.
“And then the third part which comes is, ‘Here’s our solution, which is the one that’s going to work.’ And that’s where I object.”
However, he says that – based on documents released to RNZ – New Zealand agencies have so far “largely” handled the situation appropriately.
Late last year, Earth Sciences New Zealand was awarded an $11 million Endeavour Fund grant to carry out its own research into marine carbon dioxide removal, including ocean fertilisation.
Notably, its research will not actually deploy any mCDR technology, “so avoiding technological, environmental and social-licence barriers”.
Instead, it plans to use naturally-occurring algal blooms to test advanced models and new marine carbon tracking technologies, among other things.
The agency declined an interview about this work for this story.
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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand
