To begin with, we need to define a pollutant. What is a pollutant exactly? In its broadest, and most all-encompassing sense, a pollutant is something (physical, chemical or biological) that is in the wrong place and at the wrong concentration and ends up causing harm1. Essentially, through anthropogenic activity we often move things around as we extract something in one location and move it to another location for some value adding purpose. The bigger the scale of operation, the more likely that we trigger something being in the wrong place at the wrong concentration which results in harm to something.

Timing and context is everything when it comes to pollution. For example, crude oil in deep sea deposits IS NOT a pollutant, it’s not doing any harm. Crude oil in an oil tanker following extraction from the deep sea and on its way to a refinery plant IS NOT a pollutant, it’s still not doing any harm. Crude oil seeping into the ocean from a damaged oil tanker IS a pollutant, it’s making an oil slick which is harming wildlife and the environment. Crude oil that is refined into liquid fuels and other products IS NOT a pollutant, it’s packaged up safely and is not causing any harm. Yet, the carbon dioxide generated from the combustion of crude oil products IS a pollutant, it causes global warming, ocean acidification and drives climate change.

So returning to the question at hand. Sargassum when it is free floating in the open ocean is not a pollutant: it is doing no harm. Check out the wonderful work the Sargasso Sea Commission do to protect the environment it can create. However, when it floats into the coastal regions and gets beached in excessive amounts, it becomes a pollutant: it chokes coral reefs and poses a major hazard to human and animal health, as well as decimating the local tourist and fishing industries2.

The Sargassum seaweed itself is a pollutant when it’s on the beach3, and many of its degradation products are as well, including CO2, methane and noxious sulphurous gases4. The irony is that Sargassum is only growing in these excessive amounts because it is responding (and remediating) other environmental pollutants: excessive nutrients from terrestrial run off, excessive CO2 in the oceans and, most likely, increased surface ocean temperature from global warming (temperature can be a pollutant too)5.

Sargassum is detoxifying other pollutants, but then itself becomes a pollutant by being in the wrong place (the coast) and in the wrong concentration. It turns from hero to villain in the space of a few free-drifted kilometres. But, its heroic growth is a natural response to the environmental conditions it is facing, conditions we have forced upon it and which it has responded to better than any other species. Nature has its ways of bringing balance back to ecosystems, Sargassum is part of its response.

Slowly but surely, Sargassum is cleaning up as it goes along: growing at the surface of the open ocean and sinking to the depths of the deep ocean. The process is massive and inefficient: it relies on geological scales (space and time). We aim to help Nature in this regard. It’s estimated that just 10% of the hundreds of millions of tonnes of Sargassum that grows in the great Sargassum belt ends up on the deep sea bed of the open ocean, the rest continues to shuffle around the surface ocean system cycling between trophic levels until it eventually will make it to the seabed. It is not a pollutant when it does so, this is entirely natural and has occurred for hundreds of millions of years.

Seaweed Generation aims to intercept Sargassum offshore before it becomes a pollutant, and put it on the seabed, alongside the rest of the naturally sunk Sargassum, where it is safe from doing any harm. By doing so, we accelerate the biological pump. If we remove it from the beaches when it is defined as a pollutant we would do more damage than good: there’ll be the physical damage the seaweed inflicts in however brief a time it is there, the coastal erosion caused by removal activities (e.g. sand loss), as well as a massively increased energetic burden (carbon dioxide generating) from transport and transfer far off shore for sinking. We aim to remove seaweed directly in the open ocean above deep seas and sink in situ, when Sargassum can be regarded as being at ‘peak hero’ before the rapid decline to ‘villainous zero’ can occur.

People often ask us if will we end up ‘polluting’ the seabed by doing this6. We don’t think so: Sargassum is an entirely natural biomass and the best place for it in this context is the seabed. But, there’s still the concentration issue to consider, is there a chance we can put too much down there? We think this is unlikely, the deep ocean already contains ~37 trillion tonnes of carbon7.

It’s really important to us that what we do doesn’t cause harm in any way though; it’s not a case of out-of-sight, out-of-mind for us. Seaweed Generation was created to help the Planet, not harm it. So, just in case the addition of gigatonnes of extra carbon to a system already containing trillions of tonnes does somehow have a measurable impact we are developing a monitoring program. You can see our plans here, we intend to regularly check the impact of our sinking events on the deep sea ecosystems that receive our biomass by taking visual footage, physical and chemical measurements, as well as samples for biological analysis.

Our process has many advantages when it comes to doing this: we know exactly where we are sinking and we control exactly how much we sink there. In our early years, as we scale up our operations from a few thousand tonnes a year to hundreds of thousands of tonnes a year, we will be testing out different drop densities and monitoring what happens on the seabed below. We really don’t think it will make a difference, but if we do see some form of negative perturbation we can respond easily and rapidly: there are loads of options we can explore from moving elsewhere entirely, varying drop density, cycling drop zones, to finding a different method of permanent storage altogether.

What will we be looking out for I hear you ask? Well, some of the easiest things to test for will most likely be the most enlightening. A simple measurement we will take is the oxygen levels. When you go deep down in the ocean, there’s a lot less oxygen around: usually the water hasn’t been in contact with the surface for hundreds of years so it hasn’t been replenished for a long time8. And the small oxygen that is around gets used up by microbes decomposing the material that sinks to the seabed. It’s one of the reasons why there’s not that much ‘charismatic macro’ life down there.

It’s possible that we could see a drop in oxygen levels if microbial degradation of our Sargassum happens at a such a fast rate that we can measure a difference. Alternatively, we might see an increase in oxygen levels and a potential boost to life down there. The reason we have to drop our seaweed from 200m depth is to make sure it is negatively bouyant because of all those air filled sacs they have9.

Even if the oxygen is compressed it will still be there in the air sacs, so if/when it becomes available it might end up improving microbial degradation rates and/or becoming available to some of the larger forms of life. Although our aim is to save life on the surface of the planet, we may inadvertently end up stimulating life in its deepest recesses. We have a wealth of experience on the team in environmental monitoring, in particular microbial diversity, so we are confident that we’ll be able to spot if something does happen as a result of our actions. We can respond and act accordingly in the unlikely event that we find something.

We’ll be making our samples freely available to academics who have an interest in them. We hope they’ll become a fantastic resource for the oceanic research community who often don’t have access to deep sea samples. We also hope that they can also be a source of independent corroboration/verification for our work.

If you have an interest in accessing these samples, please do get in touch, we will be happy to help. We can share our digital data freely, but physical sample holdings will be limited. We will try to accommodate as many people as possible! Priority will be given to researchers from Small Island Developing States.