Seven kilometres below the surface of the Southern Ocean, on a seabed heaped with krill poo, one of the most crucial stages of the global carbon cycle is routinely taking place. There’s little to observe, apart from the natural storage of at least 20 million tonnes of carbon each year; a process critical to the regulation of the planet’s climate.

You’d be forgiven for thinking that all the way out here, at the depth of some 7,000 metres beneath the ocean’s surface, the chance for human interference is few and far between. However, new research into the impact of microplastics on the ability for krill to absorb carbon from the atmosphere would suggest that we have – invariably – found a way.

Scientists have discovered that increased levels of plastic pollution in the Southern Ocean – and the ubiquity of micro and nanoplastics almost everywhere we now look (as well as those places we most likely aren’t) – is having an adverse effect on Antarctic krill’s carbon processing abilities.

Antarctic krill feed on phytoplankton; tiny plants that live in the ocean and absorb CO2 and remove carbon when their poo sinks to the deep ocean. Results published this month in the journal Marine Pollution Bulletin, however, demonstrate that the presence of nanoplastics (plastic particles more than 100 times smaller than the width of a human hair) in the seawater could be reducing the ability of krill poo to remove and store that CO2 by as much as 27%.

“This is huge,” said the research paper’s lead author, Clara Manno, a marine ecologist at British Antarctic Survey. “We’d already found plastic pollution in Antarctic krill from the Southern Ocean, but for the first time, we have evidence that plastic pollution could be reducing the ability of krill faeces to transport and store carbon in the deep ocean by over a quarter.”

Krill equate to roughly the same biomass as all the humans on Earth and play a vital role in locking away blue carbon in the Southern Ocean. Understanding the impact of human activities on carbon removed by the ocean is critical for informing international action on climate change.

Right now, nation leaders and representatives from NGOs and businesses across the globe are convened in Busan in the Republic of Korea to take part in the fifth and final session of the Intergovernmental Negotiating Committee to develop a legally-binding ‘instrument’ on plastic pollution, including in the marine environment.

The scope of the Treaty is to address microplastics, virgin plastic production, chemical controls, and plastic pollution prevention. Findings such as the latest from the experts at the British Antarctic Survey will be critical to conveying the importance of an effective and impactful Treaty.

“Krill are an important part of the Southern Ocean food web and are the diet of penguins, seals, and whales,” continued Manno. “Now we can see that plastic pollution is disrupting the natural role that the ocean, and climate heroes like krill, play in balancing the global carbon cycle.”

Antarctic krill form large swarms which can reach over one kilometre in length, driving a huge ‘rain’ of carbon-rich krill faeces which sink rapidly to the ocean. This poo locks away carbon from the atmosphere for extended periods of time.

According to the results of a separate, recent study led by researchers from Imperial College London and British Antarctic Survey, Antarctic krill play a key role in carbon cycling, with estimates that Antarctic krill faeces locks away at least 20 million tonnes of carbon into the deep ocean each year. This, researchers suggest, is similar to the quantities stored within key ‘blue carbon’ habitats such as mangroves, saltmarshes, and seagrasses.

To conduct the latest study, live krill samples were collected onboard the research ship RRS James Clark Ross on a science mission near the sub-Antarctic island of South Georgia. Scientists performed an experiment on the faeces produced by these animals, investigating how nanoplastic contamination affects the breakdown of the poo.

It was found that the presence of nanoplastics may encourage bacteria to decompose natural minerals, meaning krill faeces degrade more and cannot carry as much carbon as they sink to the deep ocean.

“Nanoplastics are invisible to the human eye but they can have a big impact on the environment,” said the research paper’s co-author, Emily Rowlands, a marine ecologist at the British Antarctic Survey. “Understanding that it’s not just the animals themselves being impacted but their positive role in mitigating climate change really highlights the need for global action on the issue of plastic pollution.”

Understanding how human disturbances impact carbon being locked away by krill is particularly in the Antarctic regions where krill populations are exposed to harmful human-induced effects from multiple areas, such as ocean warming, ocean acidification, and the impact of fisheries.

In an address delivered at the opening of discussions around the Plastic Pollution Treaty in Busan, Korea this week, Inger Anderson, executive director of the United Nations Environment Programme, reminded world leaders that “plastic pollution is harming the natural systems and species on which we depend – making it harder to adapt to climate change, damaging ecosystems […] and harming human health.”

“Here in Busan, we have reached the moment of truth,” she said. “This is your chance to craft an instrument for the ages. One that could deliver thousands of years free from plastic pollution. At the end of this week, the gavel must come down on an instrument that represents an ambitious starting point.

“The world wants an end to plastic pollution. The world needs an end to plastic pollution. I ask you to deliver an instrument this week that puts us on the road to delivering just that, for thousands of days, months, and years to come.”

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