When a huge tsunami triggered by the 9.0 Tohoku earthquake on March 11, 2001, destroyed coastal towns near Sendai in Japan—washing houses and cars into the swirling sea—the amount of marine debris generated from the catastrophic event was comparable to a full-year input from the entire North Pacific. Projections of where this debris might head have been made by Nikolai Maximenko and Jan Hafner at the University of Hawai‘i at Mānoa’s International Pacific Research Center. Their research is now a central part of a multiagency effort, led by the Environmental Protection Agency, to respond to issues arising from the tsunami-generated debris.
Maximenko has developed a model based on the behavior of drifting buoys deployed over years in the ocean for scientific purposes. Model simulations suggest that the majority of land- and sea-based debris, which survive multi-year travel in the North Pacific, drifts toward an area between Hawai‘i and California. The pattern of time-averaged surface currents in this “patch” corresponds to a large spiraling vortex, rotating clockwise. The model predicts that the debris will spread eastward from the Japan Coast in the North Pacific Subtropical Gyre.
In a year, the Northwestern Hawaiian Islands Marine National Monument will see pieces washing up on its shores; in two years, the remaining Hawaiian Islands will see some effects; in three years, the plume will reach the U.S. West Coast, dumping debris on Californian beaches and the beaches of British Columbia, Alaska and Baja California. The debris will then drift into the famous North Pacific Garbage Patch, where it will wander around and break into smaller and smaller pieces. In five years, Hawai‘i shores can expect to see another barrage of debris that is stronger and longer-lasting than the first one. Much of the debris leaving the North Pacific Garbage Patch ends up on Hawai‘i’s reefs and beaches.
Even before the March 11 tsunami, the world ocean was a dump for rubbish flowing in from rivers, washed off beaches, and jettisoned from oil and gas platforms and from fishing, tourist and merchant vessels. Marine debris has become a serious problem for marine ecosystems, fisheries and shipping.
Maximenko’s long-standing work on ocean currents and transports predicted that there are five major regions in the world ocean where debris collects if it is not washed up on shores or sinks to the ocean bottom, deteriorates, or is ingested by marine organisms. These regions turn out to be “garbage patches.” The North Pacific Garbage Patch was recognized in the late 1990’s, the North Atlantic Patch was fixed some years ago, and the South Atlantic, South Indian Ocean, and South Pacific patches have just been found, guided by the map of Maximenko’s model that shows where floating marine debris should collect.
These model projections will help guide clean-up and tracking operations. Tracking will be important in determining what happens to different materials in the tsunami debris, for example, how the composition of the debris plume changes with time, and how the winds and currents separate objects drifting at different speeds.
Top photo: The mass of debris stretches for miles off the Honshu Coast. Photo courtesy of the U.S. Navy.