Published: Tue, February 05, 2019
Research | By Raquel Erickson

Climate change will even change the colour of oceans, research finds

Climate change will even change the colour of oceans, research finds

Water molecules alone absorb nearly all sunlight except for the blue part of the spectrum, which is reflected back out. In areas where the tiny plants begin to die out in even greater numbers than we've seen already, those organisms will have a much tougher time sustaining themselves, and the effects are felt all the way up to the top, including humans.

Phytoplankton contain chlorophyll, a pigment that mostly absorbs in the blue portions of sunlight to produce carbon for photosynthesis, and less so in the green portions.

"The basic pattern will still be there", said Research Scientist Stephanie Dutkiewicz in a press release from MIT.

"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. Still, the sweeping alterations to sea life will be significant enough to affect ocean's food web, which phytoplankton sit at the base of.

After building their ocean model, which simulated how global warming's effects on temperature, acidification, currents and mixing will impact the metabolism and proliferation of different phytoplankton species, researchers incorporated their spectral analysis to simulate the impacts of shifts in phytoplankton communities on the ocean's color.

Since the late 1990s, satellites have been taking continuous measurements of the ocean's colour to determine the amount of chlorophyll-and, in turn, phytoplankton-in an oceanic region.

The ocean's colors could change as the climate warms, though it won't be very noticeable to the naked eye. As a result, the simulation could show changes to the light being absorbed and reflected to the ocean based on the presence of phytoplankton. This water is "barren", and the typical oceanic blue is seen in open waters. Those levels can change because of weather events or because of climate change.

The ocean is awash in blue thanks to water. But it's been hard to detect and measure these changes, says Dutkiewicz, partly because there's so much variability in the ocean from year to year.

Phytoplankton are small, microscopic plants that float through the water column, due to their ability to absorb and reflect light, communities of phytoplankton affect the color of the ocean. "So it's a complicated process, how light is reflected back out of the ocean to give it its color".

Importantly, she said, the shift in reflectance of blue/green light appeared to give an earlier indication of changes to phytoplankton than estimates of the amount of chlorophyll present, a measure now used to monitor phytoplankton levels.

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.

"It could be potentially quite serious", Dutkiewicz added of the change in color in the oceans.

When the temperature value is tweaked, the model's output shows the change in the colour of Earth's oceans: The blue and green parts of the spectrum being the most responsive, showing drastic change with increased temperatures. Since much of the ocean's color comes from phytoplankton, Dutkiewicz and her team suspected that if these communities change, then the color of the ocean is likely to vary along with them.

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