Seawater nanoplastics and krill poo: Shocking carbon impact uncovered by British Antarctic Survey researchers

Nanoplastics in the Southern Ocean may be reducing the ability of Antarctic krill to help take carbon dioxide from the atmosphere, British Antarctic Survey (BAS) researchers have warned.

The tiny shrimp-like crustaceans feed on phytoplankton - miniature plants that live in the ocean and absorb CO2. They remove carbon when their poo sinks to the deep ocean.

But increased levels of these plastic particles - more than 100 times smaller than the width of a human hair - in the seawater could reduce the ability of the krill poo to remove and store CO2 in the deep ocean by 27 per cent.

Lead author Clara Manno, a marine ecologist at Madingley-based BAS, said: “Krill are an important part of the Southern Ocean food web and are the diet of penguins, seals and whales. We had 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 – this is huge. 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.”

The biomass of krill is roughly equivalent to all the humans on Earth. They play a vital role in locking away ‘blue carbon’ in the Southern Ocean.

Forming large swarms that can reach more than a kilometre in length, they create a huge ‘rain’ of carbon-rich faeces that sinks rapidly to the deep ocean, locking away carbon for a long time.

A previous study by Imperial College London and BAS estimated that Antarctic krill faeces locks away at least 20 million tonnes of carbon into the deep ocean annually - a similar amount to key ‘blue carbon’ habitats like mangroves, saltmarshes and seagrasses.

But when researchers on board the research ship RRS James Clark Ross on a science mission near the sub-Antarctic island of South Georgia collected live krill samples and carried out an experiment on the faeces produced by them, they found nanoplastics may encourage bacteria to decompose natural materials.

This means the krill faeces degrade more and cannot carry as much carbon as they sink to the deep ocean.

Co-author Emily Rowlands, a BAS marine ecologist, said: “Nanoplastics are invisible to the human eye but they can have a big impact in the environment. 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.”

Krill populations in the Antarctic regions are exposed to harmful human-induced effects in several ways, including ocean warming, ocean acidification and the impacts of fisheries.

The results were published in the journal Marine Pollution Bulletin.