Anna Sànchez-Vidal
Professor at the University of Barcelona and a researcher with the Marine Geosciences Research Group (GMar), where she heads the research area on plastic and microplastic pollution
This is a particularly interesting and original study, which suggests that microplastics may be contributing to the colour changes observed in the ocean around the North Pacific Subtropical Gyre. Based on two decades of satellite observations and simulations, the researchers have found that the water has become brighter in both blue and green wavelengths. This pattern is consistent with the accumulation of microplastics in the water column and is difficult to explain by natural causes alone. Most importantly, it opens up a promising avenue for indirectly monitoring the smallest microplastics from space – precisely those that are the most difficult to sample and the most likely to enter the food chain.
Could this be used to monitor microplastics from space? It is a real possibility, but it is not yet an operational tool. The signal will need to be validated through oceanographic campaigns that combine measurements of microplastic concentrations with simultaneous satellite observations. It will also be necessary to check whether the method works in other regions, particularly in coastal and more productive areas, where sediments, organic matter and phytoplankton also alter the colour of the water. This would be the case in the Mediterranean, which accumulates concentrations of microplastics comparable to those in the major ocean gyres, but whose coastal waters are optically much more complex. For this reason, satellite observation and direct sampling must be viewed as complementary tools. In situ observation networks, including those involving citizen science, will be essential for validating and interpreting these signals. If their usefulness is confirmed, this could represent a very significant step forward for the global monitoring of one of the marine pollutants that is currently most difficult to quantify.