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Researchers use satellites to pinpoint polluted areas in the ocean

  • Written by  Bryony Cottam
  • Published in Oceans
Researchers use satellites to pinpoint polluted areas in the ocean NASA
18 Feb
2022
Some areas of the ocean are richer in microplastics than others. Satellites could help us identify them 

Microplastics – tiny fragments of plastic waste less than five millimetres long that have been degraded by waves, wind and ultraviolet rays – have been discovered in the deepest oceanic trenches and within the stomachs of the organisms that live there, but we have little idea about where the great majority of them end up. More than eight million tonnes of plastic enters our oceans every year, comprising between 80 and 85 per cent of all marine debris, but with scant data, there are concerns that these figures could be underestimates.

Currently, most of the data we have on microplastics are inadvertently captured by research ships, which use plankton nets to collect marine-microorganism specimens. However, researchers Christopher Ruf and Madeline Evans from the University of Michigan have discovered an innovative way to identify and track concentrations of microplastics in the ocean.

The technique relies on NASA’s Cyclone Global Navigation Satellite System (CYGNSS), a constellation of eight micro-satellites used to predict hurricanes that calculate wind speeds above the ocean by measuring the roughness of surface waters. As the satellites are continuously recording, Ruf and Evans realised that they collect a great deal of supplementary data. It was while analysing these data that they noticed some discrepancies – times where the surface of the ocean appeared to be much smoother than it should, given the prevailing wind conditions.

shutterstock 1529923664

Knowing that water isn’t roughened as much when it contains a lot of floating material, Ruf and Evans identified a pattern that linked areas of unusual smoothness and predicted microplastic distributions. They found that the difference between their measurements, and how much rougher the surface would be if winds of the same speed were blowing across clear water, was ‘highly correlated with the presence of microplastics, and the magnitude of the difference also correlated with the concentration of the plastics.’

The research reveals that there are ‘seasonal variations, where the concentrations of microplastics tend to be higher in the summer and lower in the winter in a very clean, periodic way,’ which Ruf explains mirrors the way in which the ocean circulation changes throughout the year. It also confirms, as was previously thought, that rivers are the main source of ocean microplastics. ‘By far the largest amount of outflow that we saw was coming out of the Yangtze into the East China Sea,’ says Ruf.

Raising awareness of the issue of ocean microplastics among the public and politicians is just one of the researchers’ future aims; they are also in conversation with Dutch non-profit The Ocean Cleanup and Finnish clean-technology specialist Clewat, which are interested in using the information to more efficiently target their debris-collection campaigns.

So far, only one year’s worth of data have been processed since CYGNSS was launched in 2016. By looking at a longer time period, Ruf and Evans aim to determine whether the seasonal pattern is repeatable, and whether the concentration of microplastics in the ocean is getting worse. ‘In principle, this technique ought to work with other types of motion wind satellites as well, and those go all the way back to the late 1970s,’ says Ruf.

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