The study found that climate change is changing the color of the ocean

Much like raging wildfires, scorching heat waves and plunging floods, the changing ocean color is another warning sign of human-driven climate change, according to a new study that analyzed two decades’ worth of specialized satellite observations.

Much of this change has to do with phytoplankton, which are microscopic marine algae that live in the top layer of water. Like grass and trees, phytoplankton use a green pigment called chlorophyll to convert sunlight into food.

This pigment is often seen from space, and is the main indicator scientists use to study ocean color. The study found that phytoplankton are very vulnerable to climate change – a process that expels its inhabitants from their bodies, thus changing the color of the ocean.

“It took these ecosystems millions of years to evolve together and be in balance,” said Stephanie Dutkiewicz, an MIT researcher who co-authored the study. published Last week in nature. “Changes in such a short time are not good because they throw the entire ecosystem out of balance.”

Dutkiewicz predicted those changes — and the effects they could have on marine life — in 2019. Until then, she said, satellites will be the “watchmen” in determining whether or not the ocean’s color is changing.

In the new study, the researchers first analyzed data from NASA’s Aqua MODIS satellite, which since 2002 has been monitoring ocean color changes, some of which are too subtle for the human eye to see. Twenty years’ worth of data has shown that colors have changed in more than half of the world’s oceans, according to the study. Scientists said the changes went beyond what would be expected due to natural events.

Then, to see if this trend was related to climate change, the researchers compared those results with the results of two models. Someone simulated what would happen to the ocean’s colors if greenhouse gases weren’t heating the planet, Dutkiewicz said. The model added the other in the presence of emissions, resulting in a color shift in 50 percent of the ocean — a pattern consistent with the satellite observations.

Dutkiewicz said it was a worrying sign for the future of the planet.

“I knew this could happen because I’ve been working on these models for 10 to 15 years, so it’s not surprising,” she said. “But now we can see it directly — we have an indication of it happening in the real world. And that’s scary because it means it’s not just my computer saying this anymore: It’s the satellite sensors saying, ‘Yeah, the ocean is changing color, and really fast.'”

The ocean displays a dazzling array of colors — a result of how light waves interact with molecules in the water, whether they’re scattered or absorbed, said Ivonna Cetenio, an oceanographer at NASA’s Goddard Space Flight Center. She said the composition of the ocean, or the nutrients and life it sustains, is what determines the color of its waters.

“We think of the ocean as a large body of water, but it has a great diversity of ecosystems, organisms, and nutrients,” Cetinho said. “There’s no other way to understand what’s going on and to observe all of it continuously from space – and the only way to do that is by looking at the different colors in the ocean.”

In the ocean, she said, water can have a brownish tint if it is laden with dead leaves and sediment thrown up from rivers. Elsewhere, the ocean can display a range from a deep dark blue to a shade of green—and that’s where phytoplankton come in.

In “SpongeBob SquarePants,” Plankton is a power-hungry villain. But in real life, tiny plants are responsible for up to half of the oxygen we breathe. They help absorb a lot of the carbon in the atmosphere and are the backbone of the marine food web, serving as food for zooplankton, which fish then feed on, which feed on larger fish, and so on.

Waters with a higher density of phytoplankton — such as those in the tropics — tend to appear greener, while waters with fewer phytoplankton are more blue. Now, however, the cascading effects of climate change are taking their toll on phytoplankton, Dutkiewicz said.

In some places, rising temperatures are altering ocean currents, disrupting the flow of nutrients into the deep sea that surface-dwelling phytoplankton need to survive. This lack of nutrition can reduce phytoplankton numbers – making the water more blue. In other areas, Dutkiewicz said the waters have taken on a greener hue as phytoplankton numbers increase — a boom that could be “too much” for the ecosystem to sustain.

Rising water temperatures and changes in its acidity — as more carbon dioxide dissolves into the ocean — can shift the types of phytoplankton that live in different regions. Not only does this change the color of the water, Dutkiewicz said, but it also affects food chains.

“If one phytoplankton were the size of a tennis ball, the largest would be the size of Manhattan, which means it would support completely different food webs,” Dutkiewicz said. Climate change could cause a shift equivalent to, say, the growth of palm trees in the middle of the tundra. And then you know, what do elk do because they’re not used to palm trees? “

For now, at least, it’s hard to perceive changes in the colors of the ocean with the naked eye — “It’s not like you’re going to the beach one day and it’s a different color,” Dutkiewicz said.

“But just because you can’t see it doesn’t mean it isn’t happening and that it doesn’t have the power to affect us in different ways,” Dutkiewicz added.

It should be a wake-up call, she said — “although we’ve had quite a few of those over the years.”

“It’s like we keep hitting the snooze button on our alarm telling us we have to move now,” she added.