How does plastic waste move around the Earth?

New NASA graphic shows the path of microplastics around the oceans across the Earth's surface

The researchers used NASA satellite data to track the movement of microplastics, pieces of plastic less than 5mm in diameter. Their graphics show high concentrations of microplastics in the South China Sea and Gulf of Thailand as well as the western coast of Central America.

Plastic poured into rivers or washed away by the tide at the beach circulates with the ocean currents before floating in the open sea. Plastic objects break down by waves and sunlight into microplastics, which can be mistaken for food by marine animals. Finally, plastic waste is concentrated in the center of ocean basins or subtropical ocean currents, a large rotating system of ocean currents in five oceans. The world's five subtropical ocean currents contain many islands of trash, including plastic waste, fishing lines and more. The Great Pacific Garbage Island located between California and Hawaii is most famous due to the many ships passing through.

The density of microplastics in the ocean varies by location.

About 8 million tons of plastic dumps from rivers and beaches into the ocean each year, according to NASA. The graphic created by researchers at the University of Michigan is detailed in the journal IEEE Xplore. "The density of microplastics in the ocean varies by location, especially high in the North Atlantic and North Pacific currents. We have developed a new method to detect and image the distribution of microplastics in the ocean. plastic in oceans around the globe from space," the team said.

Graphic showing the location and density of floating plastic from April 2017 to September 2018. The density of microplastics has seasonal changes. For example, in the Great Pacific Garbage Island, microplastic densities appear to be higher in summer and lower in winter. This is more likely due to the ocean's "vertical mixing" at lower temperatures. This is the up and down movement of air or sea water, which occurs due to the temperature difference between layers of water.

Scientists estimate the amount of trash in garbage islands in the sea by pulling nets behind ships. However, this method of sampling does not show how resin density changes over time. So, the team at the University of Michigan developed a new method to map the density of marine microplastics around the world. They used data from eight microsatellites belonging to the Cyclone Global Positioning Satellite System (CYGNSS).

The $157 million CYGNSS project launched in 2016 is primarily aimed at improving storm forecasting. Radio signals from GPS satellites are reflected from the sea surface and CYGNSS satellites detect that reflection. The team was then able to analyze the signal to measure sea surface variability. The measurements gave them a means of calculating wind speed and studying storms, but the signal also revealed the existence of plastic. When there is plastic or debris near the sea surface, the sea surface is less dynamic. The new method allows monitoring of microplastics in the ocean and supports the development of future models.