Denise Hardesty, senior research scientist at the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia, said this is the first estimate of how much plastic waste ends up on the ocean floor.
“We discovered that the ocean floor has become a resting place, or reservoir, for most plastic pollution, with between three to 11 million tonnes of plastic estimated to be sinking to the ocean floor,” said Hardesty, one of the corresponding authors of the study published in the journal Deep Sea Research Part I: Oceanographic Research Papers.
The researchers said their estimate of the plastic pollution on the ocean floor could be up to 100 times more than the amount of plastic floating on the ocean’s surface.
“The ocean surface is a temporary resting place of plastic so it is expected that if we can stop plastic entering our oceans, the amount would be reduced.
“However, our research found that plastic will continue to end up in the deep ocean, which becomes a permanent resting place or sink for marine plastic pollution,” said lead researcher Alice Zhu, a PhD candidate from the University of Toronto, Canada. While previous estimates looked at microplastics on the seafloor, this research looked at larger items, “from nets and cups to plastic bags and everything in between,” said Hardesty. For their study, the researchers estimated the amount and spread of the plastic pollution using predictive models, based on data from remote-operated vehicles (ROVs) and bottom trawls.
Their results also revealed that about 54 per cent of the estimated 3-11 tonnes of plastic resides in the ocean depths, from 200 metres to as deep as 11,000 metres. The remainder 46 per cent of the estimated plastic mass resides above a depth of 200 metres, the researchers said.
Inland and coastal seas are predicted to hold as much plastic mass as does the rest of the ocean floor, despite these areas covering much less surface area than oceans, they said.
“These findings help to fill a longstanding knowledge gap on the behaviour of plastic in the marine environment,” said Zhu.
With the use of plastic expected to double by 2040, understanding the pathways of plastic, including how and where it travels, is crucial to protecting marine ecosystems and wildlife, the researchers said.