In recent days, the search for the missing Malaysia Airlines jetliner has focused on blurry satellite images and other sightings of objects floating in the desolate reaches of the southern Indian Ocean.
So far, none of the objects have been retrieved or identified. They could be aircraft wreckage, but even the officials leading the search for Flight 370 acknowledge that they could be something else. And that something else, people who study marine debris say, could be just about anything.
“Any search and rescue attempt will be hampered by untold quantities of debris,” said Charles Moore, a sailor who studies marine debris at the Algalita Marine Research Institute in Long Beach, Calif. Even with relatively high-resolution satellite imaging, he said, “You are going to be confounded by the detritus of civilization.”
Nicholas Mallos, a marine-debris specialist with the Ocean Conservancy, an advocacy group in Washington, D.C., said that among the larger items found in the world’s oceans are docks, crates, containers and tangled masses of abandoned fishing nets, buoys and other gear. Even “ghost” fishing ships, 30 to 50 feet long, have washed up on coasts, he said.
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While there are no firm data about marine debris, studies of shoreline-cleanup projects and other activities suggest that four-fifths of what is floating in the ocean originates from land sources: litter and waste that is left on beaches or travels down rivers or through storm drains to the sea.
Experts agree that most debris is small and plastic — often bottles, bags and other common household or commercial items. Over time, most small plastic objects break down into even smaller particles because of the effects of waves and sunlight.
There is plenty of larger debris, too. Aside from commercial-fishing operations, where lost gear is commonplace, cargo containers account for some of it. But estimates of the number of containers that are torn from their lashings in heavy seas vary widely. Some advocacy groups claim that 10,000 or more are lost overboard each year, but the World Shipping Council, after surveying its members, estimated that about 700 is more accurate.
Natural disasters that damage structures on land, including hurricanes, typhoons and tsunamis, also contribute large amounts of debris. The tsunami that hit northern Japan in 2011, for example, washed about 5 million tons of material into the ocean, according to the Japanese government.
Even debris from the 2004 tsunami that struck Indonesia, Sri Lanka and other Indian Ocean countries is still floating around, Moore said.
It is unclear, however, how much debris from either tsunami would have traveled from the Northern Hemisphere to the Southern. Nikolai Maximenko, a researcher at the University of Hawaii, said that the equator generally acted as a wall.
“What floats in the North Pacific stays in the North Pacific,” he said. “But there are some exceptions.”
Much of the marine debris, large and small, is concentrated in gyres, large oceanic regions with circulating currents. It was Moore’s encounter with one of these areas — now known informally as the Great Pacific Garbage Patch — while sailing from Hawaii to California in the 1990s that inspired him to start the Algalita institute.