Half of the Ocean's Surface Has Changed Color. That Shouldn't Happen.
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Human-driven climate change is altering the world’s oceans, including their very color.
New research from MIT, U.K.’s National Oceanography Center, and NASA shows that 56 percent of the world’s oceans have become more green over the past 20 years.
This new green hue is likely due to changes occurring in the phytoplankton community, which lives near the ocean’s surface.
Anthropogenic greenhouse gasses are forever altering the world’s landscape. Changing weather patterns are choking some parts of the world with drought while flooding others in a cacophony of hurricanes and superstorms. But these changes don’t just affect climate — they can also impact the very color of the planet’s oceans.
New research from MIT, the National Oceanography Center in the U.K, and NASA shows that about 56 percent of the ocean’s surface is slowly changing color due to human-induced climate change. Although the change doesn’t cover the entire ocean—the tropical seas near the equator are particularly affected—the effects still span a larger area than are covered by all landmasses on Earth. The results of the study were published in the journal Nature on Wednesday.
“I’ve been running simulations that have been telling me for years that these changes in ocean color are going to happen,” Stephanie Dutkiewicz, MIT senior research scientist and co-author,said in a press release. “To actually see it happening for real is not surprising, but frightening. And these changes are consistent with man-induced changes to our climate.”
The main engine behind aquatic color is light absorption. H2O molecules absorb warmer wavelengths of light—red, yellow, and green—better than blue. In fact, at around 100 meters deep, red light is absorbed completely. This is why the ocean slowly becomes a richer blue the farther you descend into its depths. Although water isn’t great at absorbing blue, it does eventually get the job done, which is why the deepest parts (anything below about a kilometer) are pitch black.
But deep blue hue of the ocean is created by a variety of factors, and the color at the ocean’s surface can also be influenced by the lifeforms and ecosystems living there. One big example is phytoplankton, a plant-like microbe that lives in the upper ocean and contains the greenish pigment chlorophyll. Phytoplankton are arguably the most important organisms on Earth, as they’re responsible for producing 70 percent of the world’s oxygen, capturing carbon from the atmosphere, and providing the nutritional foundation for a vast web of marine life.
Scientists keep an eye on phytoplankton by measuring how much blue-green light is reflected by the ocean’s surface from space. For 20 years, scientists have tracked phytoplankton, and this new paper shows that in those two decades, the majority of the ocean (though mostly imperceptible to our eyes) has only gotten greener.
While researchers are still unsure of precisely how the undersea ecosystems are shifting to cause this color change, they’re pretty sure the plankton are heavily involved. “The color of the oceans has changed,” Dutkiewicz said in a news release. “And we can’t say how. But we can say that changes in color reflect changes in plankton communities, that will impact everything that feeds on plankton. It will also change how much the ocean will take up carbon, because different types of plankton have different abilities to do that.”
The researchers used the Moderate Resolution Imaging Spectroradiometer (MRIS) aboard NASA’s Aqua satellite. While the dataset showed clear variability, researchers compared the data to two climate models—one with excess greenhouse gasses and one without—to determine if the color change was simply annual variability.
Sadly, it was not.
“This suggests that the trends we observe are not a random variation in the Earth system,” lead author B. B. Cael said in a press release. “This is consistent with anthropogenic climate change.”
Climate change is one of the greatest challenges humanity’s ever faced, and for the world’s oceans—especially for its essential community of phytoplankton—we’re quickly entering a “sink or swim” moment.
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