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Garbage patches in the ocean are sobering reminders of humanity’s collective plastic pollution problem. Measuring up to thousands of kilometers across, the patches have been confirmed to exist in the Pacific and Atlantic Oceans, but not in the Indian—a surprise, given that more plastic waste enters the Indian Ocean than anywhere else on Earth.
According to a new study led by Mirjam van der Mheen, a doctoral candidate at the University of Western Australia, the Indian Ocean’s unique geography, ocean currents, and atmospheric conditions actually appear to be preventing waste from piling up in a garbage patch.
Pinpointing where all the plastic goes, says van der Mheen, is a huge challenge.
“The technology to remotely track plastics in the ocean does not yet exist,” explains van der Mheen. “There aren’t many measurements of marine plastic debris, so it is not straightforward to predict how plastic waste is transported once it enters the ocean.”
Since they couldn’t track individual pieces of plastic, the team used the next best thing: GPS data from more than 22,000 buoys that have drifted around the oceans since 1979. Running the data through computer simulations provided a picture of how floating objects are pushed around by currents and wind.
The simulations show that multiple physical forces prevent the formation of an Indian Ocean garbage patch. In the south Indian Ocean, an unusually persistent equatorial countercurrent flows from west to east across the basin, scattering a trail of submerged plastics all the way to Australia.
Additionally, strong easterly monsoon winds move buoyant surface debris in the opposite direction, toward the African coastline.
Because the south Indian Ocean’s gyre extends just past the southern tip of Africa, plastics accumulate here briefly, then move out past South Africa into the southern Atlantic Ocean.
These transient accumulations of plastic debris near the coast pose a serious threat to marine biodiversity—as highlighted by recent reports from South Africa of dead sea turtle hatchlings washing ashore with plastic in their guts.
The modeling research also indicates the possibility of a garbage patch forming in the Bay of Bengal, although more measurements of plastic concentrations are needed to confirm this.
The Indian Ocean’s dispersed plastic debris may be more difficult to clean than waste concentrated into a garbage patch, says van der Mheen. Even so, knowing how floating debris moves through the ocean can help identify common movement pathways—what she calls “plastic highways”—where converging waste flows could one day be intercepted.
These results have implications for those studying plastic pollution in other oceans. Understanding the forces driving Indian Ocean plastic movement “will result in a better description of surface dispersion at the global scale,” says Christophe Maes, an oceanographer at France’s Laboratoire d’Océanographie Physique et Spatiale.
Yet with plastic waste piling up on some of the Indian Ocean’s most remote beaches, the key to halting the pollution crisis lies further up the supply chain, says Annett Finger of Australia’s Victoria University. “The only viable solution is to reduce plastic production and consumption while improving waste management to stop this material entering our oceans in the first place.”