Climate change is causing a shift in the color of the oceans, an early indicator of important changes to marine ecosystems, according to a study done by MIT.
The change in temperature is having an effect on phytoplankton, microscopic organisms that live in the water and that absorb and reflect light wavelengths.
A model developed by the study’s researchers shows that by 2100, climate change will cause more than 50 percent of the oceans to change color. In effect, blue parts of the ocean will become a deeper blue and green parts a deeper green. Even though the human eye may not be able to see the color adjustments, satellites will be able to to detect them.
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“The model includes equations for what is happening in the atmosphere, how the atmosphere is moving around and being heated,” Stephanie Dutkiewicz, a principal research scientist at MIT’s Department of Earth, Atmospheric, and Planetary Sciences, said. “It includes equations for how the ocean is moving, taking up heat and mixing up nutrients.”
The researchers take what they know about the real world to create a virtual world using those rules.
“We can also simulate the future, assuming things like how the CO2 content of the atmosphere is going to change and how humans will impact CO2 emissions,” she said.
The color of the ocean is dependent on how sunlight interacts with what is in the water. When there is no phytoplankton present, the ocean appears as deep blue from outer space. However, when there is a lot of phytoplankton, the ocean looks green because the chlorophyll in the phytoplankton absorbs the blue portions of sunlight in order produce more carbon for photosynthesis.
The subtropics, the vast regions just north and south of the equator, and much of the North Atlantic are projected to get bluer. Small regions in the Southern Ocean and parts of the Arctic are expected to get greener.
Phytoplankton live at the sunlit layer of the ocean, but to survive, they need nutrients from the bottom of the ocean. Natural causes, like an El Niño or La Niña, cause a fluctuation in the amount of nutrients that phytoplankton get and in turn, the color of the ocean to change.
Dutkiewicz’s previous studies show that changes in carbon emissions have a big impact on the phytoplankton. As the climate changes, not only does the color of the ocean change, but the food web that phytoplankton supports is affected.
So why does this matter?
“The oceans modulate our climate in a very big way,” Amala Mahadevan, a physical oceanographer at Woods Hole Oceanographic Institution, said. “The oceans, thanks to phytoplankton which functions like a plant, take up about two thirds of the CO2 we put into the atmosphere because of the fossil fuels we are burning. The oceans are offsetting the effect of climate change for us. If they had not done that, our temperatures would be much higher.”
If phytoplankton change, the ocean would no longer absorb CO2 at the same rate.
“All other organism depend on phytoplankton, they are the base of the food chain in the ocean, Mahadevan said. “If you change the phytoplankton, you change everything, including the fish that you eat.”
Dutkiewicz stressed the need for satellites to be maintained by programs like NASA in order to continue to monitor the change of the color of the ocean.
“Just because you can’t see it, climate change is real and if we were to reduce the amount of greenhouse gasses we were admitting into the environment, it would reduce the impact of change that the model suggests,” Dutkiewicz said.