Between a quarter and a third of all the carbon dioxide humans produce every year gets absorbed by the ocean. Not by machines we built or forests we planted – just by the ocean, doing what it’s always done.
And a huge part of how it does that comes down to organisms so small you can’t see them: phytoplankton.
These are single-celled algae drifting in the upper layers of the sea, converting sunlight and CO2 into oxygen and sugar through photosynthesis.
Phytoplankton are one of the most important things on the planet. And they now share the ocean with something that’s getting in their way.
Microplastics are everywhere in the ocean now, until the most remote stretches of open water on Earth.
A new study led by the Norwegian University of Science and Technology (NTNU) set out to investigate what is all that plastic actually doing to the ocean’s ability to absorb carbon?
The research was led by Francesca Verones at NTNU’s Department of Energy and Process Engineering.
Small particles, several problems
Scientists collected phytoplankton data from climate zones around the world and combined it with laboratory data on how microplastics affect algal growth.
The team used the results to calculate the impact of different plastic concentrations on carbon uptake, both regionally and globally
“The ocean plays a crucial role in absorbing carbon from the atmosphere. Between 25 and 30 per cent of all human-generated CO2 is absorbed by the ocean,” Verones said.
“Phytoplankton plays an important role in this process. So, what happens if marine microplastics affect the plankton?”
The answer is: several things, none of them good.
Some plastics – PVC in particular – are directly toxic to algae. Others block sunlight from penetrating deep into the water, which limits photosynthesis.
Microplastics can physically damage algae cells, or trigger oxidative stress that disrupts how they function.
Most vulnerable places are hit hardest
The most troubling finding is a geographic one.
The regions where microplastics cause the most damage to carbon uptake are the same regions where carbon uptake matters most: arid and tropical zones.
In those areas, the researchers calculated that microplastics could reduce carbon absorption by 25,000 tons per year in arid regions and 48,000 tons in tropical ones.
“We must bear in mind that the amount of microplastics in the ocean is increasing all the time,” Verones said.
“All the plastic that is discarded in the natural environment will eventually end up in the ocean. So the concentrations are going to keep on increasing.”
The bigger picture
This study is part of a broader EU-funded project examining plastic’s impact on the ocean through what researchers call a life cycle assessment.
This is a framework that traces a product’s environmental footprint from manufacture through use to disposal and eventual breakdown.
The idea is to stop looking at environmental problems one at a time and start seeing how they connect.
The triple planetary crisis
The project has three strands. One tracks how plastic harms marine biodiversity – through animals swallowing it, getting tangled in it, or being physically damaged by it.
A second examines how floating plastic spreads invasive species across oceans, carrying organisms into waters they’d never naturally reach.
The third – this study – asks what plastic does to ecosystem services, starting with carbon uptake.
Those three strands map onto what the UN has called the “triple planetary crisis”: climate change, biodiversity loss, and pollution.
They tend to get treated as separate problems with separate budgets and separate summits. In the real ocean, they’re the same problem, happening to the same water, affecting the same organisms at the same time.
Broader implications of the study
This is the first study to specifically calculate how plastic affects ocean carbon uptake and fold that finding into a life cycle assessment.
The fact that it took this long is a quiet indictment of how siloed environmental research has been, keeping the plastic, carbon, and biodiversity crises separate.
Phytoplankton are easy to overlook. They’re invisible and they live far from most of the places humans pay attention to.
Their work – photosynthesis happening in billions of microscopic cells across the world’s oceans – goes completely unnoticed unless something starts to go wrong with it.
Something is starting to go wrong with it. And unlike a changing climate or a shifting ocean current, this is a problem we are manufacturing ourselves and shipping into the sea every single day.
The study is published in the journal Ecosystem Services.
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