Plastic Bag Found in the Mariana Trench: What It Means

The discovery of a plastic bag in the Mariana Trench, the deepest point on Earth, serves as a symbol of human impact. This finding highlights that no corner of the planet is untouched by our waste. The presence of refuse in a place of such extreme depth challenges the perception of the deep ocean as a pristine frontier, revealing it as a final repository for debris.

The Factual Account of the Discovery

In May 2019, explorer Victor Vescovo made a record-breaking solo dive to the Challenger Deep, the deepest point within the Mariana Trench. During this mission, he descended nearly 11,000 meters (approximately 36,000 feet) in his submersible. The expedition’s goal was to map the world’s five deepest points and collect biological and geological samples.

From his submersible, Vescovo observed what appeared to be man-made waste on the seafloor. While initial reports cited a plastic bag and candy wrappers, Vescovo later clarified that it was difficult to identify the object without retrieving it. He described seeing a small, triangular object he believed was “probably plastic,” confirming the presence of debris in this inaccessible environment.

This was not the first time plastic had been documented at such depths, as a 2018 review of deep-sea photos had already recorded a plastic bag nearby. Vescovo’s expedition, however, brought renewed focus to the issue through a direct observation made during a historic dive.

Pathways to the Deepest Ocean

Plastics like polyethylene, initially less dense than seawater, float on the surface and are transported by vast, circulating ocean currents known as gyres. These currents carry debris for thousands of kilometers from coastal areas, shipping lanes, and rivers to remote parts of the ocean.

For buoyant plastic to sink, its density must change through biofouling or aggregation with marine snow. Biofouling begins when microorganisms and larger organisms colonize the plastic’s surface. This accumulation of life, known as the “plastisphere,” adds weight to the debris, causing it to lose buoyancy and sink.

As the plastic descends, it can become entangled with “marine snow,” a continuous shower of organic detritus falling from the upper ocean. This sticky matter aggregates with the plastic, accelerating its descent. Once debris enters a trench like the Mariana, deep-sea currents can funnel and concentrate the material, trapping it on the seafloor.

Consequences for the Deep Sea Ecosystem

The arrival of plastic in the Mariana Trench has implications for its ecosystem. In the deep sea, the absence of UV light and cold temperatures cause plastic to degrade extremely slowly, allowing it to persist for centuries. Over time, larger items break down into smaller fragments known as microplastics. These tiny particles litter the seafloor and contaminate the sediment.

Deep-sea organisms can mistake these microplastics for food. Studies have confirmed the ingestion of microplastics by hadal amphipods, which are small, shrimp-like crustaceans from the Mariana Trench. Research found that over 72% of these creatures had ingested at least one man-made particle, which can cause internal blockages and starvation.

This contamination cascades up the food chain as predators consume smaller organisms that have ingested plastic, a process called trophic transfer. Plastics can also alter the physical habitat of the seafloor and introduce toxins or invasive microbes. The presence of plastic in this ecosystem demonstrates a direct biological impact of human activity on life at every ocean depth.