According to a study published Wednesday in Nature, the change is due to a variation in ecosystems, and in particular plankton, which is the centerpiece of the marine food system and plays a crucial role in the global carbon cycle and in the production of the oxygen we breathe.

"The reason we are interested in colour changes is that colour reflects the state of the ecosystem," lead study author B.B. Cael of Britain's National Oceanographic Centre told AFP.

The color of the seas, seen from space, can indeed give an idea of what is happening in the upper layers of the water: a deep blue means that there is little life, whereas if the water is greener, it is likely that there is more activity, especially from phytoplankton which, Like plants, contains a green pigment bound to chlorophyll.

Far from being trivial, the evolution of phytoplankton and its concentration in certain regions, to the detriment of others where it could disappear, could disrupt the entire marine food chain.

Scientists therefore want to develop ways to monitor these changes in ecosystems in order to monitor climate change and establish protected areas.

Nature's study broadened the color spectrum, examining seven ocean color hues monitored by the MODIS-Aqua satellite from 2002 to 2022. These hues are too subtle to be perceived by humans and appear largely blue to the naked eye.

Its authors compared observational data to computer models of climate change. They concluded that the observed changes were closely in line with what had been predicted by the models.

"I've been doing simulations for years that tell me that these changes in ocean color are going to happen. To see that this actually happens is not surprising, but frightening," said Stephanie Dutkiewicz, co-author of the study and a member of MIT's Department of Earth, Atmospheric and Planetary Sciences.

While further work is needed to determine the exact implications of color changes, the study's authors believe it is very likely that climate change is the cause.

"These changes are consistent with what is known about the changes produced by human activities on climate," Dutkiewicz said.

© 2023 AFP