A recent animation released by Nasa researchers shows how the plastic that is dumped into oceans moves around the world.
Every year, an alarming eight million tons of plastic flows from rivers and beaches into oceans, and Nasa’s animation — the first of its kind on a global scale — shows the location and concentration of floating plastic over a period of 18 months.
This plastic is broken down into microplastics over time, thanks to ocean currents and sunlight. Scientists usually measure marine garbage patches — areas in the ocean where the debris collects — by dragging nets behind boats.
But this sampling method is “geographically sparse and does not give researchers a sense of how much plastic concentrations change over time”, according to a statement by Nasa’s Earth Observatory.
And so, researchers at the University of Michigan recently developed a new method to map ocean microplastics around the world. Nasa said that they used data from eight microsatellites that are part of the Cyclone Global Navigation Satellite System (CYGNSS) mission.
“Radio signals from GPS satellites reflect off the ocean surface, and CYGNSS satellites detect those reflections,” Nasa said.
Scientists analysed these signals and measured the roughness of the ocean surface — which then helped them find out ocean wind speeds. “It turns out that the signals also reveal the presence of plastic,” researchers said.
Chris Ruf, principal investigator of the CYGNSS mission and one of the researchers, explained that when there is plastic or other debris presents on the water surface, the sea surface is not as rough as it would be otherwise.
“In cleaner waters, there’s a high degree of agreement between ocean roughness and wind speed. But as you head into the Great Pacific Garbage Patch [between California and Hawaii], you see a bigger discrepancy between wind speed measurements and the roughness of the surface,” he said.
Mr Ruf and University of Michigan research assistant Madeline Evans used this data to map concentrations of microplastics across the ocean for more than a year.
The data helped researchers understand some seasonal variations in microplastic concentrations. “In the Great Pacific Garbage Patch, for example, microplastic concentrations appear greater in the summer and lower in winter, perhaps due to more vertical mixing of the ocean when the temperatures are cooler,” Nasa said in its statement.
They also created time-lapse views of all of the major rivers across the world and noted “particularly large amounts of microplastics” coming from the Yangtze river in China and India’s Ganges.
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