Scientists at the University of Michigan (USA) have developed, on the basis of data from a NASA satellite system, a new method for recording the global distribution of microplastics in the world's seas from outer space. From the satellite data of a NASA system close to the earth, they calculated the concentration and movements of plastic particles in the sea. According to the research team, the study also provides information on discharges of microplastic from rivers and also gives indications that the concentration of microplastic on the water’s surface changes with the seasons.

 

The calculation of the concentrations of microplastic close to the ocean surface by the scientists at the University of Michigan is based on measurements from the Cyclone Global Navigation Satellite System (CYGNSS). It consists of eight small satellites that were developed to research and predict hurricanes and whirlwinds. The system measures by radar between latitude 38° north and 38° south the turbulence on the surface of the sea in order to calculate the wind speeds. The research team from the University of Michigan used the data from the observation range of the CYGNSS system to estimate microplastic concentrations. The authors of the study worked on the assumption that the presence of microplastic can be read from the size of the divergence between the calculated wind speed and the measured turbulence data. Their hypothesis was that if plastic or other litter is present close to the ocean surface, as for example in the Great Pacific Garbage Patch between California and Hawaii, the waves will be muted and the surface of the sea is less rough than it would be without the litter. In order to establish where the water was less agitated than would be expected, Chris Ruf, lead researcher in the CYGNSS project and one of the authors of the research study, compared, together with co-author Madeleine Evans, the CYGNSS turbulence measurements with other measurements of the wind speeds of buoys and other instruments. They combined their analyses with earlier models of plastic waste in the sea and thus charted the concentrations of microplastic in the ocean as a whole. According to Ruf and Evans, there should, in waters less polluted with waste, be a high level of conformity between the roughness of the sea and the wind speed: "But the further you go into the Great Pacific Garbage Patch, the greater is the discrepancy between the measurements of the wind speed and the roughness of the sea. When plastic particles are near to the ocean surface, the water is calmer and fewer waves are formed," explains Ruf. Over and above this, the data also indicate some seasonal fluctuations in the microplastic concentration. In the Pacific Garbage Patch, for example, the microplastic concentration seems to be higher in the summer and lower in the winter, which the research team attributes to a more pronounced vertical turbulence of the ocean at cooler temperatures. As a result, less microplastic is identified close to the surface.

For the study, Ruf and Evans also produced time-lapse recordings of all the world's major rivers, and concluded that particularly large quantities of microplastic stem from the Yangtze and the Ganges. According to the results obtained by the research team, the study shows on the one hand that microplastic in the sea suppresses the turbulence on the surface through winds. Secondly, the concentration of the microplastic correlates with the level of suppression. Based on this correlative relationship, Ruf and Evans have developed an algorithm which, they say, can be used for producing time-lapse recordings of the global and regional microplastic distribution. As a result, NASA has used the study data to produce an animated world map, which, according to the space agency, charts for the first time the global distribution and movements of microplastic in the oceans over such a long period.

 

Further information: to the study "Toward the Detection and Imaging of Ocean Microplastics with a Spaceborne Radar", to the NASA map

 

Sources:

• eu (7.12.2021)
• nasa.gov (3.12.2021)
• Toward the Detection and Imaging of Ocean Microplastics with a Spaceborne Radar, Madeline C. Evans, Christopher S. Ruf, published in "IEEE Transactions on Geoscience and Remote Sensing", (9.6.2021)
• Photo: NASA