CANBERRA, Australia — The great Pacific garbage patch, a gigantic floating island of trash spanning an area twice the size of the state of Texas, is plain to see. Now, new international research reports there’s much, much more trash residing below the ocean’s surface. CSIRO, Australia’s national science agency, and researchers from the University of Toronto in Canada estimate there are up to 11 million tonnes of plastic pollution on the ocean floor.
Still not concerned? Every single minute, a garbage truck’s worth of plastic enters the ocean. With the use of plastic predicted to double by 2040, grasping precisely how and where all that plastic travels after being thrown away is crucial to protecting marine ecosystems and wildlife. Dr. Denise Hardesty, Senior Research Scientist with CSIRO, explains this is the first ever estimate of how much plastic waste ends up on the ocean floor specifically, where it accumulates before eventually breaking down into smaller pieces and mixing into ocean sediment.
“We know that millions of tonnes of plastic waste enter our oceans every year but what we didn’t know is how much of this pollution ends up on our ocean floor,” Dr. Hardesty says in a statement. “We discovered that the ocean floor has become a resting place, or reservoir, for most plastic pollution, with between 3 to 11 million tonnes of plastic estimated to be sinking to the ocean floor.”
“While there has been a previous estimate of microplastics on the seafloor, this research looks at larger items, from nets and cups to plastic bags and everything in between,” Hardesty continues.
Alice Zhu, a PhD Candidate from the University of Toronto who led the study, adds that according to the latest estimates, the amount of plastic pollution on the ocean floor could be up to 100 times more than the levels of plastic found 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,” Zhu says. “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.”
Researchers utilized a set of scientific data to construct two predictive models for estimating both the amount and distribution of plastic on the ocean floor; one model came via data collected by remote-operated vehicles (ROVs), while the other used data from bottom trawls. Using the ROV data, study authors estimated three to 11 million metric tonnes of plastic pollution resides on the floor of the ocean.
The ROV results also revealed mass clusters of plastic around continents; approximately half (46%) of the predicted plastic mass on the global ocean floor resides above 200 m depth. Deeper areas of the ocean, from 200 meters to as deep as 11,000 meters, contain the remainder of the predicted plastic mass (54%).
While inland and coastal seas cover much less surface area than oceans (11% vs 56% out of the entire Earth’s area), researchers estimate these regions hold as much plastic mass as the rest of the ocean floor.
“These findings help to fill a longstanding knowledge gap on the behavior of plastic in the marine environment,” Zhu concludes. “Understanding the driving forces behind the transport and accumulation of plastic in the deep ocean will help to inform source reduction and environmental remediation efforts, thereby reducing the risks that plastic pollution may pose to marine life.”
The study is published in Deep Sea Research Part I Oceanographic Research Papers.