Climate change will even change the color of the oceans, study says

Olive Hawkins
February 5, 2019

Climate change is changing populations of small, microscopic algae that float through the water column known as phytoplankton.

The oceans appear blue because water molecules alone absorb nearly all sunlight except for the blue part of the spectrum, but with any organism in the ocean, phytoplankton for instance, the pigment in it will absorb less in the green portions and reflect more green light.

By the year 2100, they say more than 50 percent of our oceans will have shifted in color, and those regions in the subtropics and near the equator and poles will have brighter blues and deeper greens most visible through satellite images of the Earth.

"In the same way that plants on land are green, phytoplankton are green as well, so the amount and different types of phytoplankton affect the colour of the ocean surface", said Dr Anna Hickman, co-author of the research from the school of ocean and earth science at the University of Southampton.

Dutkiewicz says ocean warming is already changing the types of phytoplankton and where they live. "That basic pattern will still be there".

The team modelled what would happen to the oceans by the end of this century if the world warmed by 3C, which is close to where temperatures are likely to be, if every country sticks to the promises they have made in the Paris climate agreement.

The team combined a system looking at changes to the hue of the ocean over the last two decades with one that predicted how phytoplankton would react to rising temperatures and ocean acidification-where the pH level of the water becomes more acidic as the ocean absorbs more carbon dioxide from the atmosphere.

To find out how much climate change will influence the ocean's color, the researchers built a model that simulates how ocean color will shift based on the amount and type of phytoplankton present. Their model can estimate wavelengths of light that are absorbed and reflected by the ocean, which obviously changes by a given region and the organisms in the water. "Phytoplankton are at the base, and if the base changes, it endangers everything else along the food web, going far enough to the polar bears or tuna or just about anything that you want to eat or love to see in pictures".

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Regions where there are a lot of nutrients, like in the Southern Ocean or parts of the North Atlantic, will see even faster-growing phytoplankton because those waters are warming with climate change.

"Without them there wouldn't be any life in the ocean", says MIT's Stephanie Dutkiewicz, lead author on the new study. On the other hand, colder algae-rich green waters in cold regions will also get warmer, potentially spurring the growth of more diverse phytoplankton.

One way to monitor changes on a global scale is through observing the color of the ocean satellite data.

The ocean looks blue or green to us because of a combination of how sunlight interacts with water molecules and with whatever else lives in that water.

Costa hopes this latest report will reinforce the importance of understanding the effects of climate change on the world's oceans, noting phytoplankton are "very important in the carbon cycle".

"Sunlight will come into the ocean, and anything that's in the ocean will absorb it, like chlorophyll", Dutkiewicz says. Dutkiewicz said those instruments will probably provide early signals of how climate change is altering the oceans and their colour.

The simulations, which take about three weeks to run on a large array of computers, revealed we can expect our oceans to look a little different in the future, though it depends on where you go. By the end of the century, our blue planet may look visibly altered.

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