How circulation patterns of surface currents could help clean the Great Pacific Garbage Patch

Between Hawaii and California, trash swirls in giant ocean currents, caught up in the infamous, Texas-sized Great Pacific Garbage Patch. This is just one of many found across the globe. Efforts to clear the patch with sweeping nets may be well-intentioned, but the financial and environmental costs of fuel make them controversial.

A study published in Ocean Science has analyzed surface currents as observed from satellites to identify regions that—due to their circulation patterns—attract objects drifting nearby into large garbage patches.

“With this information, we can let the currents do the work. Instead of boats slowly trawling and burning fuel, they can hold their position and keep the nets steady at a location where currents funnel and aggregate drifting objects which will theoretically save cleanup crews time, money and fuel,” said Planetary Science Institute Research Scientist Rodrigo Duran. He is the paper’s only co-author based in the U.S.

Luca Kunz, a graduate student at the University of Hamburg, is the lead author.

“Sir Isaac Newton was the first to solve trajectory problems while trying to understand celestial bodies orbiting within a gravity field. But, he was thinking in terms of how Earth orbits the sun,” Duran said.

“Over the following centuries, new tools and ideas were used to solve these kinds of extremely complicated problems. However, it wasn’t until the last couple of decades that these tools were adapted to surface ocean currents and wind, which bring an additional level of complexity. It’s not like the equations of gravity, which remain predictable for a very long time. The ocean is always changing.”

To understand the variable ocean, the research team combined over 20 years of ocean current satellite data with data collected by floating sensors, called drifters, that ride ocean currents and record their trajectories.

From this data, they identified and categorized 3.5 million Transient Attracting Profiles, or TRAPs for short, which are regions where drifting objects—including garbage—aggregate, brought together by two or more groupings of eddies, or circular currents. Each eddy can be anywhere between 60 to 180 miles wide and amass drifting objects into a region larger than a city, or about 60 miles at its widest, Duran said. These structures come and go, but on average, they’re stable for six days.

The most common and efficient TRAPs form when four eddies join up in a certain configuration: If laid out in four quadrants, eddies spinning counterclockwise would be in the top right and bottom left quadrants, while eddies spinning clockwise would be in the top left and bottom right.

“This is almost 60% of cases,” Duran said. “These are common because they are the most stable.”

Because these structures tend to organize how things move with currents and wind this work can be used in many different scenarios, according to the research team.

“An obvious example would be search and rescue of missing people,” Duran said, “or maybe a cargo ship loses their cargo. This can even be used for atmospheric data. When volcanoes erupt or wildfires break out, airports need to know whether to redirect flights. It’s a very exciting time.”

The research paper was written in collaboration with the University of Hamburg and The Ocean Clean Up, a Netherlands-based non-profit organization developing technologies to rid the world’s oceans of plastic.