I was at the wheel of a 54-foot research sloop crossing the north Pacific Ocean through the heart of one of the most plastic-polluted parts of the sea, when I spotted my first piece of floating plastic debris. It was a shredded corner of a sun-bleached orange fish crate. Minutes later, I saw a chunk of white foam drift by and then a pink dustpan. Next, there went a green cosmetics bottle, but soon after, it was clean deep blue sea again.

I’d been at sea for nearly two weeks in November 2016, sailing from California to Hawaii with a group of Danish sailors and scientists. Up until that day, the only plastic I’d seen was the tiny broken-up bits of "microplastic" the scientists had scooped out of the water with manta trawls and other sampling equipment. But as the trip progressed, some days I saw lots of larger floating junk, sometimes very little and sometimes none. It’s well known that circulating currents called gyres concentrate plastic over large areas of the ocean’s surface, but I wondered what was behind the day-to-day variations in trash.





New research published in January in the Proceedings of the National Academy of Sciences may help shed light on the phenomenon I witnessed at sea.

To date, scientists have largely thought that floating debris concentrates in certain areas of the ocean as the result of surface currents and winds. In the new study, however, scientists tracked the motion of drifting buoys deployed in the Gulf of Mexico and discovered another way that plastic congregates: downwelling, which occurs in areas where surface water sinks and is pulled down as in a bathtub drain, with water moving toward the vortex.

The study’s lead author, Eric D’Asaro, said the newly established relationship between downwelling and floating debris concentrations could be used to pinpoint accumulations of ocean pollutants for cleanup. The study was funded by the Gulf of Mexico Research Initiative, an independent research initiative established after the 2010 Deepwater Horizon oil spill, but its findings can be applied to anything floating on the ocean’s surface, whether spilled oil or plastic debris.

"It emphasizes that the distribution of buoyant material can be very non-uniform … and opens the possibility of predicting where such concentrations will occur," said D’Asaro, a University of Washington oceanographer. "And if you know where oil is, it’s easier to recover."

To emulate an oil spill, which spreads quickly to cover large swathes of ocean, researchers tossed GPS-equipped, donut-shaped drifter buoys made of a biodegradable plastic called polyhydroxyalkanoates (PHAs) and smaller bamboo drift cards, designed to float with currents. The buoys and cards were deployed from two research vessels over hundreds of miles in the Gulf over a stormy 30 days during the winter of 2016.

To track them, scientists used satellites and helium balloons and planes that took high-resolution and infrared imagery. Autonomous ocean gliders and other instruments collected real-time data on local atmospheric and ocean conditions, such as water density and wind speed.

Instead of staying spread out, as the scientists’ calculations predicted, within eight days half of the 326 drifters and drift cards used in the experiment moved together in clusters into a space smaller than a football stadium. In these areas, the buoys’ GPS data indicated strong downward movement, as if they were being pulled below the surface. Atmospheric and oceanic data collected in these zones confirmed the existence of downwelling vortices.

"I did not really expect such an amazing amount of convergence," said D’Asaro.





This latest research builds off a similar but smaller 2012 effort that collected data about drifting items on the ocean’s surface. Together, the research suggests that in areas where water masses of different densities — varying in temperature or salinity — converge, vortices form and aggregate floating debris on the ocean’s surface. According to experts, this explains the behavior of the drifting items found at small-scale convergence zones in this study — and probably was what I saw at sea.

"In general, we have a very good understanding, on ocean basin scales, where to expect accumulations of floating debris, but it has not been so easy to explain very small-scale variations," she said. "Anecdotally, we have observed — from the deck of the ship — long lines of accumulated debris, which could have been caused by the mechanism described."

If there’s a way to predict where convergence zones form, concentrated oil spills and plastic pollution could be easier to track down and clean up. Law said this new knowledge of convergence zones also could be helpful in rescuing a lost ship or airplane or may even help improve models that seek to determine where a lost vessel, oil spill or concentration of plastic debris originated. That could help, eventually, get to the root of the plastic pollution problem.

Kara Lavender Law, a professor of oceanography at the Sea Education Association (SEA) who was not involved in the study, called the research a "tremendously successful project."

For important news about our world’s oceans, sign up to the Oceans email list. By Erica Cirino





The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. An independent and academic 20-member Research Board makes the funding and research direction decisions to ensure the intellectual quality, effectiveness and academic independence of the GoMRI research. All research data, findings and publications will be made publicly available. The program was established through a $500 million financial commitment from BP. For more information, visit

Social scientists documented a series of shared effects on residents of the five U.S. Gulf Coast states following the Deepwater Horizon incident. They noted that unlike natural disasters when people tend to come together and help one another, human-induced incidents and related response efforts tend to cause discord. Feelings of stress, anger, and mistrust arise in affected communities, particularly among groups who feel their livelihoods threatened.




OCEAN CONVERGENCE AND THE DISPERSION OF FLOTSAM - PNAS 2018; published ahead of print January 16, 2018

Eric A. D’Asaro, Andrey Y. Shcherbina, Jody M. Klymak, Jeroen Molemaker, Guillaume Novelli, Cédric M. Guigand, Angelique C. Haza, Brian K. Haus, Edward H. Ryan, Gregg A. Jacobs, Helga S. Huntley, Nathan J. M. Laxague, Shuyi Chen, Falco Judt, James C. McWilliams, Roy Barkan, A. D. Kirwan, Andrew C. Poje and Tamay M. Özgökmen.


Contributed by Eric A. D’Asaro, December 11, 2017 (sent for review October 25, 2017; reviewed by Thomas Farrar and Patrice Klein)



Ocean currents move material released on the ocean surface away from the release point and, over time, spread it over an increasingly large area. However, observations also show high concentrations of the material even after significant spreading. This work examines a mechanism for creating such concentrations: downwelling of water at the boundaries of different water masses concentrates floating material at this boundary. Hundreds of satellite-tracked drifters were released near the site of the 2010 Deepwater Horizon oil spill. Surprisingly, most of these gathered into a single cluster less than 100 m in size, dramatically demonstrating the strength of this mechanism.



Floating oil, plastics, and marine organisms are continually redistributed by ocean surface currents. Prediction of their resulting distribution on the surface is a fundamental, long-standing, and practically important problem. The dominant paradigm is dispersion within the dynamical context of a nondivergent flow: objects initially close together will on average spread apart but the area of surface patches of material does not change. Although this paradigm is likely valid at mesoscales, larger than 100 km in horizontal scale, recent theoretical studies of submesoscales (less than ∼10 km) predict strong surface convergences and downwelling associated with horizontal density fronts and cyclonic vortices. Here we show that such structures can dramatically concentrate floating material. More than half of an array of ∼200 surface drifters covering ∼20 × 20 km2 converged into a 60 × 60 m region within a week, a factor of more than 105 decrease in area, before slowly dispersing. As predicted, the convergence occurred at density fronts and with cyclonic vorticity. A zipperlike structure may play an important role. Cyclonic vorticity and vertical velocity reached 0.001 s−1 and 0.01 ms−1, respectively, which is much larger than usually inferred. This suggests a paradigm in which nearby objects form submesoscale clusters, and these clusters then spread apart. Together, these effects set both the overall extent and the finescale texture of a patch of floating material. Material concentrated at submesoscale convergences can create unique communities of organisms, amplify impacts of toxic material, and create opportunities to more efficiently recover such material.



Satellite plot of dispersed marker buoys in ocean currents






New plastic economy circular materials challenge



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