It’s not just ocean waters that are warming. They have also started to change color

Climate change is changing the oceans forever. Global warming has led to… Polar ice is disappearing fasterthat hurricanes and natural disasters are becoming more frequent and that many marine organisms are dying They are moving To areas they had never lived before. There is another, equally important, though less well-known, result: the seas are changing colour.

Become greener. This is what comes out of Study published in Nature who analyzed 20 years of NASA satellite images. The results reveal dramatic changes in the color palette in 56% of the seas during that period, especially in tropical regions located within 40 degrees of the equator. It’s all about marine organisms, and more specifically phytoplankton.

Investigation. B.B. Kyle and his colleagues at the National Oceanographic Center in Southampton analyzed the observations made by the planet NASA’s MODIS Aqua satellite He has done it for the past 20 years and looked for patterns of change in ocean color across a range of colors that includes red and blue. When comparing these changes with assumptions from a computer model simulating what the oceans would have looked like if global warming had never occurred, the contrast is clear.

In most areas there was a clear “green effect”.

Darker purple means a more significant color change.

Why does this happen? Phytoplankton contain the pigment chlorophyll, which reflects green light, making the ocean greener when it hosts a greater number of these marine microbes. And as the study authors explain, so do plankton It scatters and absorbs light differently, changing the optical properties of the water and, therefore, the reflectance (which is ultimately the color we perceive of the ocean). If the reflection changes, it means that the ecosystem is changing.

Stratification. The authors believe that the likely origin of this change occurs in… Nutrient stratification is fueled by climate In the upper waters of the oceans, which may cut off food sources for these organisms. “More stratification means a greater difference in density of surface water (where the light is) versus deep water (where the nutrients are), which means less mixing of the two, which means fewer nutrients getting to the plankton,” Kyle explained.

Why should we care? Not because of the color of course, although we all love the refreshing blue, but because it strongly demonstrates that the marine ecosystem is changing. It should be taken into account that phytoplankton play their role An essential role for all life on Earth as a global carbon sink A producer of atmospheric oxygen.

They also have the ability to change much of their environment, including temperature, nutrient availability, and light levels in the water. Base of the marine food chain. For all this, it is important to know what exactly is happening to them and how we can solve it.

Photos | Unsplash/National Oceanographic Center

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*An earlier version of this article was published in July 2023.