We’ve spoken to a lot of scientists about this. The ones on our team, the ones on our Scientific Board, and many who are working on and thinking about the oceans, seaweed, carbon cycling, air sea flux and more. Our conclusion from these conversations is: we don’t know for sure. Some feel that naturally occuring biomass may stimulate deep ocean life, some worry it will impact it, often this will depend on the amounts of additional biomass you’re talking about. Scientists studying the oceans often have wildly differing opinions. The reason for that is fairly simple - there isn’t a lot of data, especially about the deep ocean. That’s one thing that most scientists do agree on, we need more data. That’s an ongoing effort that we will contribute to in our 2023 pilot.

Even so, it’s important to point out that we wouldn’t believe ocean based CDR to be a viable gigatonne removal pathway if we thought it would do harm. Our reasoning for this is fairly simple.

The deep ocean contains 37 trillion tonnes of carbon - the upper ocean contains around 900 billion tonnes, and the atmosphere around 875 billion tonnes. The deep ocean is orders of magnitude (16x1) richer in carbon than the upper carbon cycle. Humanity’s total emissions from pre industrial times would be a 2% increase in deep ocean carbon content2.

Evenly distributed, 10 gigatonnes a year of carbon dioxide removal to the ocean at depths of 1000 metres or more using macroalgae would add 8.62g or 862mmol of biomass per square metre. That is a 12x increase compared to the natural rate of deep ocean marine snow, which is estimated to be around 800 million tonnes of carbon per year3, and is considered to be a key stimulant to deep ocean life. The distribution of this biomass is highly variable. Usually it’s a constant flow of plankton, fish waste, organic breakoff. But the ocean also copes with huge influxes of biomass on a regular basis - marine snow is by no means evenly distributed, often occurring (though significantly less frequently these days) in the form of huge marine carcasses.

When weighing the pros and cons of any action, we should consider what humanity needs to do to combat climate change. As many say “we’ve already done enough damage”. That is sadly all too true. We have changed an entire planet’s ecosystem, in a geological blink of an eye. It is frightening. We need to actively undo this harm we have inflicted - reducing our footprint by 75% and removing (not offsetting, removing) the remaining 25% of our annual emissions.. That isn’t going to be easy and it needs to be done at a huge scale. And quickly. Then there’s the social, political, environmental and health aspects of this story which are all entwined. Sargassum is a massive problem. It’s an utter menace. People will often say to us  “oh yes, I saw the Sargassum, it ruined our holiday”. Terrible stuff indeed, but imagine if instead of two weeks exposure and having to remain by the hotel pool (albeit somewhat ruined by the stench of rotting material), you actually lived with this problem day in, day out?

If we leave things as they stand and do nothing, we will see millions of people across the Caribbean and West Coast of Africa continue to suffer. And it’s spreading: it’s starting to push north, and we’re seeing it increasing in abundance in Florida and Western Europe. Does that make a difference, when the problem is closer to home? Not for us. But for many maybe it will.

Kaiko, a deep sea ROV, (which, out of interest, is currently lost for good on the deep sea bed somewhere after its tether snapped) managed to capture a photographs of deep ocean life during one of its expeditions, proving that life can survive even in the crushing pressure of Mariana’s deepest reaches. There is life down there, and we should nurture it.

We are environmentalists first and foremost, and we care about what is doing there and the impact of what we are doing. Indeed, our extensive monitoring program will provide plenty of new information and data about the deep ocean, and we’ll be sharing that freely with the academic community. Through our work, people will have a greater understanding of the deep sea, because we’ll be visiting regularly and seeing if the entirely natural biomass we add impacts on the ecosystem. What if we see perturbations in e.g. a sediment worm population though? Then we can change how we do things by changing location and loadings. We can work to stabilise and alter our biomass. We can seek different depths and types of ocean sediment, or, we can, and will walk away from Ocean based CDR altogether.

To not do anything at all because we might see a perturbation is not an option for millions of people who are directly affected in the region, as well as the billions of people who are all now starting to feel the effects of climate change. You could consider it a simple trade off: is it acceptable to allow the destruction of coral reefs and allow animals like turtles to go extinct at the surface of the planet?

What about the direct human cost? Sargassum blooms are a recent phenomenon, since 2009 really. The long term impacts on human health have barely been assessed. Hydrogen sulphide (a degradation product from Sargassum) leads to fatal hypoxic pulmonary, neurological, and cardiovascular lesions in high concentrations45. In low concentrations, though chronic exposure as seen in the Caribbean, it can lead to conjunctival and upper airway irritation, headaches, vestibular syndrome, memory loss, and modification of learning abilities. These don’t present in clinics commonly, they are ‘soft’ symptoms which are hard to put your finger on. But many teenagers in the Caribbean will have been exposed to these compounds every year since their birth, what will the long term impact be? It’s a ticking time bomb. The data is starting to come through now though: a recent study of 154 people presenting in clinic following a 2018 stranding episode in Martinique found neurological (80%), digestive (77%) and respiratory (69%) disorders were the most frequent reasons for medical visit6. The timings of medical visits was related to the stranding events, and the geographical origin of the patients was consistent with the worst impacted areas. Slowly, the pieces of the real picture are falling into place: Sargassum is a major international public health concern.

So, we have a major international public health concern, a global climate crisis and a solution that mimics an entirely natural, proven process that could be a big part of solving the problem..

Yes, we should operate with necessary and appropriate caution. But no, we should not do nothing.The planet is hurting, we need to properly assess all possible pathways to fixing it.