FunNature & AnimalThe ocean is changing color because of climate change

The ocean is changing color because of climate change

The color change will be almost imperceptible to the human eye, but it could hint at the profound changes that are expected for marine life.

At the heart of this ocean-changing phenomenon are tiny marine microorganisms called phytoplankton, which are crucial to ocean food webs and the global carbon cycle – and sensitive to ocean water temperatures. Due to the way light reflects off organisms, blooms from these phytoplankton communities create colorful patterns on the ocean’s surface.

Climate change will fuel phytoplankton bloom in some areas, while reducing it in other places, leading to subtle changes in the ocean’s appearance.

The color of the ocean varies from green to blue, depending on the type and concentration of phytoplankton or algae in any area. A deep blue ocean generally means little phytoplankton. The more phytoplankton, the greener the water looks.

According to NASA, when sunlight hits the ocean, some of the light is directly reflected, but most of it penetrates the ocean’s surface and interacts with the water molecules it encounters. By looking closely at the ocean’s colors, scientists can better understand phytoplankton and how they impact the world around them.

“Color will be one of the first signals, ” says Stephanie Dutkiewicz, of the Center for the Science of Global Change at MIT and co-author of the study published in the journal Nature Communications. “We will be able to see, not with the naked eye but through instruments, that the color of the ocean has changed.”

Phytoplankton live on the surface of the ocean, where they use sunlight and carbon dioxide to photosynthesize. When these organisms die, they bury carbon deep in the ocean, a crucial process that helps regulate the global climate.

But phytoplankton are vulnerable to the current ocean warming trend . According to NASA, warming changes key properties of the ocean and can affect phytoplankton growth, as they not only need sunlight and carbon dioxide to thrive, but also nutrients.

“Productivity is expected to decline because as surface waters warm, the water column becomes more and more stratified; there is less vertical mixing to recycle nutrients from deep waters to the surface,” they explain.

Various scientific models suggest that there is likely a decrease in the total amount of phytoplankton in the oceans over time.

Scientists built a climate model that projects changes in the oceans, including their optical properties, over the century. And in a world warming to 3 degrees Celsius, he found that multiple changes would occur in the color of the oceans.

The world has already warmed more than 1 degree since the 19th century, and at the current rate, scientists predict that warming could accelerate in the coming decades if nations do not take serious steps to reduce carbon dioxide emissions.

And why does that matter?

Phytoplankton communities are the foundation of the food web and are extremely diverse. If certain types begin to disappear from the ocean “it will change the type of fish that can survive,” the experts explain. Such changes could have an impact on the food chain.

Any color change in ocean experiences over the next several decades will likely be too gradual and subtle for most people to notice, but in the scientific world, they could spell significant changes.

“The changes are occurring due to climate change. It will take a while before we can prove it statistically. But the change in the color of the ocean will be one of the first warning signs that we have really changed our planet,” say the experts.

Reference: Ocean color signature of climate change. Stephanie Dutkiewicz, Anna E. Hickman, Oliver Jahn, Stephanie Henson, Claudie Beaulieu & Erwan Monier. Nature Communications volume 10, Article number: 578 (2019) DOI: https://doi.org/10.1038/s41467-019-08457-x

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