Climate change is changing the ocean’s color — and fast, scientists say
Beachgoers around the world would probably give different descriptions of the ocean. Those gazing at the Caribbean Sea might describe clear or turquoise water, while those along Argentinas coastline, where major rivers empty into the Atlantic Ocean, could report a light brown, sediment-rich view. But even though seawater has always differed depending on location, season or currents, scientists say the color of more than half of the worlds oceans is changing and fast. Much like raging wildfires, scorching heat waves and drenching floods , the oceans changing color is yet another warning sign of human-driven climate change, according to a new study that analyzed two decades worth of specialized satellite observations. Much of that change has to do with phytoplankton, the microscopic marine algae that live in the waters upper layer. Like grass and trees, phytoplankton use a green pigment called chlorophyll to convert sunlight into food. That pigment is often seen from space, and its the main indicator scientists use to study the oceans color. But phytoplankton are very susceptible to climate change a process thats throwing their populations out of whack and, thus, changing the oceans color, the study found. These ecosystems have taken millions of years to evolve together and be in balance, said Stephanie Dutkiewicz, a researcher at the Massachusetts Institute of Technology who co-authored the study, which was published last week in Nature. Changes in such a short amount of time are not good because they put the whole ecosystem out of balance. Dutkiewicz predicted those changes and the effects they could have on marine life in 2019. And even then, she said satellites would be the sentinels in determining whether the oceans color was shifting. In the new study, the researchers first analyzed data from NASAs Aqua MODIS satellite, which since 2002 has been monitoring ocean color changes, some of which are too subtle for human eyes to see. Twenty years-worth of data showed that colors had shifted in more than half of the worlds oceans, the study states. And scientists said the changes went beyond whats expected due to natural occurrences. Then, to find out whether that trend was related to climate change, the researchers compared those findings with the results of two models. One of them, Dutkiewicz said, simulated what would happen to the oceans colors if greenhouse gases werent heating the planet. The other model added in the presence of emissions, which resulted in a shift in color in 50 percent of the ocean a pattern consistent with the satellites observations. Dutkiewicz said it was a worrisome sign for the future of the planet. I knew that this could happen because Ive been working on these models for 10 to 15 years, so its not surprising, she said. But now we can see it firsthand we have a signal of it going on in the real world. And thats frightening because it means its not just my computer saying this anymore: Its satellite sensors saying, Yes, the oceans color is changing and really fast. The ocean displays an impressive range of colors a result of how light waves interact with the molecules in the water, getting either scattered or absorbed, said Ivona Cetinic, an oceanographer with NASA Goddard Space Flight Center. The oceans composition, or the nutrients and lives it sustains, is what defines the color of its water, she said. We think about ocean as this big bunch of water, but it has a huge variation in ecosystems and organisms and nutrients, Cetinic said. Theres no other way of understanding whats happening and observing all of that continuously than from space and the only way we can do it is by looking at the different colors in the ocean. In the ocean, water can have a brownish tint if its loaded with dead leaves and sediments spewing from rivers, she said. In other places, the ocean can showcase a range from deep navy blue to a greener-looking shade and thats where phytoplankton come into play. On the show SpongeBob SquarePants, plankton is a power-hungry villain. But in real life, the tiny plants are responsible for up to half of the oxygen we breathe. They help suck up much of the atmospheres carbon and are the backbone of the marine food web, serving as food for zooplankton, which then get eaten by fish, which fuel even bigger fish, and so on. Water that has a larger density of phytoplankton like that in the tropics tends to look greener, while water with fewer phytoplankton is bluer. Now, however, the cascading effects of climate change are taking a toll on phytoplankton, Dutkiewicz said. In some places, rising temperatures are changing ocean currents, disrupting the flow of deep-sea nutrients that surface-dwelling phytoplankton need to survive. That lack of nutrition can decrease phytoplankton populations turning the water bluer. In other areas, Dutkiewicz said the water has taken on a greener tint as phytoplankton populations increase a boom that can be too much for the ecosystem to sustain. Warmer water and changes in its acidity a product of more carbon dioxide dissolving into the ocean can also transform the species of phytoplankton that live in different areas. That not only changes the waters color but also affects food chains, Dutkiewicz said. If one phytoplankton was the size of a tennis ball, the largest would be the size of Manhattan, meaning they are going to support very different food webs, Dutkiewicz said. Climate change can cause a shift equivalent to, say, having palm trees grow in the middle of a tundra. And then you know, what do the elks do since theyre not used to palm trees? For now, at least, the changes in the oceans colors are hard to perceive with the naked eye its not like youre going to go to the beach one day and its a different color, Dutkiewicz said. But just because you cant see it, it doesnt mean its not happening and that it doesnt have the capability of impacting us in different ways, Dutkiewicz added. She said it should be a wake-up call though weve gotten quite a few of those over the years. Its almost like we keep pressing the snooze button on an alarm thats telling us we have to act now, she added.