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Microplastics - tiny pieces 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 percent of all marine trash, but with inadequate data, there are concerns that these figures could be underestimates.

Currently, most of the data we have on microplastics are accidentally captured by research ships, which use plankton nets to collect marine-microorganism samples. 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 additional data. It was while analysing these data that they noticed some differences-times where the surface of the ocean appeared to be much smoother than it should, given the prevailing wind (盛行风) conditions.

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 degree 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.

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 Duteh non-profit The Ocean Cleanup and Finnish clean-technology specialist Clewat, which are interested in using the information to more efficiently target their trash-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 micmplastics in the ocean is getting worse.