For the preparation of the work, which has the participation of the CSIC, an organization dependent on the Ministry of Science, Innovation and Universities (MICIU), and has been financed by the European Space Agency (ESA), a historical series of six years of observations was analyzed. of the European Copernicus Sentinel-2 satellite in the Mediterranean. In total, 300,000 images taken every three days with a resolution of 10 meters were scrutinized. The results reveal large aggregations of garbage and debris within floating structures scientifically known as “trails” that can be several kilometers long and result from the convergence of marine currents and the effect of wind on the sea surface.
Although the satellite’s sensors were not specifically designed to detect garbage, its ability to identify plastic made it possible to create a map of the most polluted areas of the Mediterranean. This map shows the main garbage entry points from the continent and improves our understanding of the mechanisms that transport waste. The results indicate that the amount of floating plastic in the Mediterranean could cover an area of approximately 95 square kilometers during the period 2015–2021, which is equivalent to about 7,500 football fields.
“Until now, searching for aggregations of garbage several meters in diameter on the surface of the ocean was like looking for needles in a haystack, since the formation of trails requires the presence of a large amount of garbage and little wind to prevent it from dispersing,” points out Manuel Arias, researcher at ICM-CSIC and one of the co-directors of the work.
For his part, co-director of the study Andrés Cózar, from the University of Cádiz emphasizes that “the relevance and meaning of the trails in terms of marine litter was, until now, an unknown.” Automation through supercomputers and advanced search algorithms has made it possible to prove that it is possible to monitor the accumulation of marine litter from space in large areas and on a routine basis.
Faced with future space missions, the research team suggests installing specific sensors for the detection of plastics in satellites. According to the study, this would multiply the ability to detect plastic in the ocean by twenty. Furthermore, this information could be compared with other environmental factors to improve understanding of the mechanisms that transport plastic waste from land to sea, and better guide actions and regulations to combat this form of marine pollution that affects both biodiversity and fishing resources and tourism.
Population Density, a Key Factor
The study concludes that factors such as population density, geography, or rainfall significantly influence the accumulation of garbage in the sea. Thus, for example, desert countries or cities contribute much less to the problem, while in areas with more rainfall, especially when torrential rains occur, the accumulation of garbage resulting from emissions that occurred in the previous days and weeks is much greater.
Finally, the study reveals that, for the most part, the garbage of continental origin is confined to the first 15 kilometers of sea from the coast, returning to it after a few days or months. “This confirms the notion that the distribution of garbage of continental origin and that generated by human activities directly in the sea behave and distribute in a different way,” Arias details in this sense.
The authors of the study illustrate the applicability of the new methodology with several real cases, such as the evaluation of the effectiveness of action plans against litter in the Tiber River in Rome (Italy), the identification of pollution sources related to transportation maritime in the Suez Canal (Egypt) or the use of satellite observations to guide cleaning tasks in the waters of the Bay of Biscay (Spain).
All in all, the results of the work show that monitoring marine pollution through satellites is feasible and promising for issues beyond plastic. For example, a sensor specifically dedicated to the detection and identification of floating objects could help address problems such as cargo loss on ships, oil spills or search and rescue at sea.
In addition to the University of Cádiz and the ICM-CSIC, the work team is made up of researchers from the European Space Agency (ESA), ARGANS France, the Universitat Politècnica de Catalunya (Spain), the Consiglio Nazionale delle Ricerche (ISMAR-CNR , Italy), the Technical University of Crete (Greece), ARGANS Ltd. (United Kingdom), AIRBUS Defense and Space (France), the Joint Research Center (JRC) of the European Commission, The Ocean Cleanup (Netherlands), and ACRI-ST (France).
