Harder than finding a needle in a haystack: spotting "plastic soups' in the ocean?

A French team of researchers from the Ocean Scientific Logistic association (OSL) is setting sails to the Hawaiian Islands –more precisely to the "Seventh Continent," the name given to the huge cluster of plastic waste floating midwater of the North Pacific, over an area six times the size of France. Far from trade routes, nearly 3.5 million tons of plastic are floating there, in the first 30 meters below the water surface.

The goal of this expedition is to collect samples of water and waste to develop a new way of locating layers of plastic debris using satellites. Surprising as it seems, the ocean's garbage patches are hard to locate –and are actually divided in at least five different zones around the globe.

"The ‘Seventh Continent" is not strictly speaking an island we can walk on," says George Grepin, the OSL's biologist. "It's more like a soup made up of billions of plastic pieces the size of a confetti or even invisible to the naked eye. "Under the action of the sun and of currents, bottles, plastic bags and other containers lost at sea end up slowly decomposing to form particles as small as plankton, on which fish feed.

"With our partner, the National Center for Spatial Research (CNES), we hope to check whether, under certain conditions, satellites can spot these debris," says George Grépin.

Satellite lenses are not sharp enough to spot plastic micro-debris. "The best satellites, that is, the Pléiades satellites, are equipped with optical sensors that can take pictures of Earth with a resolution of about 70 centimeters," says CNES's Danielle Staerke. "This is not enough to allow us to see debris that is usually 100 times smaller. Still, if these particles of waste are present in sufficient quantity, they are likely to modify the texture of the water. This effect should be visible on radar images and that's what we are going to check."

The ocean's plastic pollution has a particularly harmful impact on marine life, the most obvious being the risk of animals choking after ingesting floating debris, as well as the accumulation of toxic particles in the food chain.

But this vast "plastic soup" also has more surreptitious effects: the ocean progressively becomes a plastic heaven for a certain species of water striders --the Halobates sericeus-- that usually lay their eggs on rocks… or on floating objects. A study led by Miriam Goldste from San Diego's Scripps Institution of Oceanography shows that the insect has taken advantage of the situation to proliferate. "We don't know exactly what the consequences of this phenomenon are so far," Goldstein says. "But if it gets worse, there will be a risk of endangering the balance of marine ecosystems."

Read more from Le Temps in French. Full story by Caroline Depecker.

Photo – NOAA Marine Debris

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