Garbage patch in the North Pacific breaks down and pollutes the deep sea

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Manta trawl was deployed from the starboard crane to collect data on plastic pollution in the ocean’s surface. (Image Credit: Ocean Cleanup)

Plastic debris can be quite hazardous to marine life in a number of ways, from toxic chemical release to animal entanglement, wildlife choking and starvation after consuming it, and the distribution of harmful organisms. Researchers from Ocean Cleanup discovered that pieces of the plastic debris in the North Pacific Garbage Patch (NPGP) have been lost to the underlying deep sea through the vertical transfer of microplastics. The team published their findings in Scientific Reports on May 6^th, 2020.

Studies conducted on plastic pollution in the Great Pacific Garbage Patch mostly focused on plastic fragments floating at the sea surface. In 2018, the Ocean Cleanup’s System 001 (dubbed “Wilson”) deployment and monitoring phase presented researchers with an opportunity to dive into the water column to examine the vertical extent of plastic pollution in the area. To perform these tasks, the Ocean Cleanup used a monitoring vessel, the Maersk Transporter, which was rigged with a Multiple Opening and Closing Net with an Environmental Sensing System (MOCNESS) containing 9 mesh nets that allowed the team to gather samples from the ocean’s surface down to 2000m depths.

Five of the study sites in the eastern North Pacific Ocean from Honolulu, Hawaii, to Rosarito, Mexico, were used to investigate the vertical distribution of plastic debris. (Image Credit: Ocean Cleanup)

Overall, more than 12,000 pieces of plastic measuring 0.5mm or larger were gathered from the NPGP and analyzed at Rotterdam Zoo facilities. The researchers discovered that the amount of plastic fragments in the water column increased with higher concentrations at the sea surface. Interestingly enough, what also came to light is that the plastic bits in the water column were mostly made of polyethylene and polypropylene, which are the primary types of plastic floating in the NPGP. This observation is strongly indicative of a vertical transfer of microplastics from the NPGP into the deep sea.

Exactly how these microplastics reach deeper depths of water is still a mystery, but a number of sedimentation mechanisms have been proposed. They include changes in buoyancy due to biofouling (colonization of bacteria, algae, and other marine organisms), manifestation into marine snow, and fecal pellets, along with aggregation with suspended particles. However, the quantitative importance of these proposed mechanisms is still unknown.

The sedimentation of floating microplastics from the ocean surface is frequently used as an explanation for missing plastics, which refers to the estimates of the number of plastics entering the ocean and the number drifting at the surface. The researchers’ latest study shows hints of a possible subsurface plastic mass reservoir in the NPGP. At five study areas, the team discovered that 90% of the mass in the upper 2000m of the water column was concentrated in the top 5m. The other 10% was scattered across water depths of 5-2000m.

Visual representation showing the vertical numerical and mass concentrations of plastic debris found below the garbage patch in the Pacific Ocean. (Image Credit: Ocean Cleanup)

It’s imperative to understand that these numbers represent a “preview” of the vertical distribution of the patch while sampling in November-December 2018. Additional data will need to be gathered to study how time and location can affect plastic concentrations in the water column underneath the NPGP. The researchers are still collecting data spanning extensive spatial scales while taking temporal aspects into consideration. These measurements are required in order to quantify the amount of plastic debris currently in the water column below the NPGP and in the oceans around the world.

The research shows that plastic pollution has already entered the deep sea below the NPGP. It’s still unknown how it will affect the widely undiscovered ecosystem. On a more positive note, the available data reveals that most of the pollution found in the NPGP is still floating on the ocean surface. This makes it possible to diminish the impact it could have on deep-sea ecosystems underneath the garbage patches. Removing debris floating in the waters will significantly lessen the number of microplastics sinking into deeper waters. Once it has sunk below the ocean surface, it will be much more difficult, if not impossible, to clean up microplastics in the ocean.

To help eliminate plastics in the great pacific, Ocean Cleanup designed and developed a system that relies on natural forces, such as wind, waves, and currents to carry the system and plastic patches. The system is compromised of a long floater that sits atop of the water’s surface and a skirt that hangs just below it. The floater helps to provide buoyancy to the system, and the skirt keeps the debris from being released underneath and guides it into a retention system, or cod end. There is also a cork line above the skirt to prevent overtopping and keeps the skirt afloat. To capture the plastics ranging from small millimeter-sized pieces to large debris, a difference in speed is required between the system and plastics. A sea anchor creates a drag to help the system move slowly, allowing the plastic to be retained and captured.

Models reveal that using a full-scale cleanup system roll-out could eliminate up to 50% of the NPGP in five years. After groups of these systems are placed in all the ocean gyres, coupled with source reduction, The Ocean Cleanup predicts it will remove approximately 90% of plastic debris by 2040.

Here are a couple picture of a small part of the garbage patch... it's startling.

(Image credit: Forbes)

(Image credit: Storyful)

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