Ocean floor harbors up to 11 million tons of plastic debris 

The ocean floor harbors up to 11 million tons of plastic debris, according to new findings from CSIRO, Australia’s national science agency, in collaboration with the University of Toronto in Canada.

With the alarming rate of one garbage truck’s worth of plastic being dumped into the ocean every minute, and projections indicating a potential doubling of plastic use by 2040, grasping the dynamics of plastic’s journey through marine environments is essential for the preservation of marine life and habitats.

A resting place for plastic pollution 

“We know that millions of tons 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,” said co-author Denise Hardesty, a Senior Research Scientist at CSIRO. 

“We discovered that the ocean floor has become a resting place, or reservoir, for most plastic pollution, with between 3 to 11 million tons 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.” 

Enormous amount of ocean floor plastic

The study, led by Alice Zhu, a PhD candidate at the University of Toronto, reveals that the amount of plastic found on the ocean floor could surpass surface plastic by up to 100 times. 

“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,” Zhu explained.

Mapping plastic on the ocean floor 

To quantify and map the distribution of oceanic floor plastic, the research team developed two predictive models, leveraging data from remote operated vehicles (ROVs) and bottom trawls. Findings from ROV data indicate that an estimated 3 to 11 million metric tons of plastic litter the ocean’s depths.

Furthermore, the study indicates that plastic tends to aggregate around continental masses, with nearly half (46%) of the estimated plastic mass on the global ocean floor located above 200 m depth, while the remaining 54% is distributed in deeper waters, down to 11,000 meters.

Despite their smaller surface area compared to open oceans (11% versus 56% of the Earth’s total area), inland and coastal seas are thought to contain an equivalent amount of plastic mass as the rest of the oceanic floor combined.

Permanent plastic sink

“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 said. “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.”  

“These findings help to fill a longstanding knowledge gap on the behavior of plastic in the marine environment. 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,” she concluded.

Impact on ocean ecosystems 

Plastic pollution has a profound and multifaceted impact on ocean ecosystems, affecting nearly every level of the marine food web. Here are some of the key ways through which plastic impacts these environments:

Entanglement and ingestion

Marine animals, including seals, whales, turtles, and birds, can become entangled in plastic waste like fishing nets, six-pack rings, and plastic bags. This can lead to injury, illness, suffocation, starvation, and even death. Ingestion of plastic particles is also common, which can block digestive tracts, lead to starvation, and introduce toxic substances into the organisms.

Toxicity

Many plastics leach harmful chemicals, including bisphenol A (BPA), phthalates, and other endocrine disruptors, into the water. These chemicals can accumulate in the food chain, affecting reproduction, growth, and survival of marine life. Additionally, plastics in the ocean can adsorb pollutants from the surrounding water, further increasing their toxicity to marine organisms that ingest them.

Habitat disruption

Large accumulations of plastics can alter marine habitats. For instance, floating plastics can block sunlight from reaching photosynthetic algae and seagrasses, crucial sources of oxygen and food for many marine ecosystems. Plastic debris can also smother coral reefs, disrupting the delicate relationships between corals and the myriad of species that rely on coral ecosystems.

Microplastics and nanoplastics

As plastics break down into smaller pieces, they create microplastics and nanoplastics, which are especially problematic. These tiny particles can be ingested by a wide range of marine organisms, from plankton to larger fish, often with lethal outcomes. They can also carry harmful bacteria, introducing diseases to coral and other marine life.

Economic impact

Beyond ecological damage, plastic pollution affects economic activities like tourism, fishing, and shipping. Beaches littered with plastic waste can deter tourists, while fishing industries suffer when marine life is killed or contaminated by plastics. Shipping routes can also be impeded by large accumulations of floating plastic debris.

The study is published in the journal Deep Sea Research Part I: Oceanographic Research Papers.  

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