More than half of the oceans have changed color – DW – 13/07/2023

Although our eyes do not perceive it with the naked eye, the color of the ocean has changed dramatically in the past 20 years, According to a study published in nature, This change as a result of climate change caused by the man.

study, led by scholars From the Massachusetts Institute of Technology (MIT) and the National Oceanography Center in the United Kingdom, reports that this change has been detected in 56% of the world’s oceans, an expanse greater than the total surface area of ​​the Earth.

The article explains that the tropical ocean regions Near the equator they become greener, indicating that surface ecosystems are also changing, because the ocean’s color is a “literal” reflection of the state of the organisms and materials in its waters.

Researchers still can’t say exactly how marine ecosystems are changing, but they are sure it’s caused by climate change.

said Stephanie Dutkiewicz, study co-author and research scientist at MIT.

phytoplankton

The color of the ocean reflects what is in the upper layers: deep blue waters reflect very little life, and greener waters indicate existence of ecosystems, Mainly from phytoplankton – plant-like microbes that abound in the upper layers of the ocean.

Phytoplankton are the foundation of the marine food web that supports progressively more complex organisms, including krill, fish, birds and marine mammals, and they are also a powerful muscle in the ocean’s ability to capture and store carbon dioxide.

That’s why scientists have spent decades observing phytoplankton at the ocean’s surface and studying how these core communities respond to climate change, observing from space.

Aqua satellite imagery

Kyle and his team analyzed measurements of ocean color with the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite, which has been monitoring ocean color for 21 years and makes measurements at seven visible wavelengths.

And although much of the ocean appears blue to our eyes, true color can contain a mixture of more subtle wavelengths, from blue to green and even red.

Cael conducted a statistical analysis using the seven ocean colors measured by satellite between 2002 and 2022. He first looked at how much the seven colors changed from one region to another over the course of a year, then extended the analysis to two decades.

The analysis showed a clear trend, above normal annual volatility.

To see if the trend is related to climate change, he turned to Dutkiewicz’s 2019 model, which simulates Earth’s oceans in two scenarios: one with greenhouse gases added and one without.

The greenhouse gas model predicted that a major trend would emerge within 20 years and that this trend should cause ocean color changes in about 50 percent of the world’s surface oceans (exactly what Kyle found in his analysis of real-world satellite data).

“The color of the oceans has changed, because it reflects changes in plankton communities, which will affect anything that feeds on plankton.”

“These changes will also change how much carbon the ocean will absorb, because different types of plankton have different capacities to do so. So we hope people will take it seriously. It’s not just models that predict these changes. Now we can see it. The ocean is changing,” Dutkiewicz said. “.

FEW (EFE, nature)