Published: Tue, February 05, 2019
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Climate change will dramatically alter colour of Earth's oceans

Climate change will dramatically alter colour of Earth's oceans

In order to account for these natural events, the researchers tweaked a previous global model used previously to predict phytoplankton changes in response to rising temperatures and ocean acidification to instead predict how climate change is affecting phytoplankton.

"It's an important variable that we should be tracking to understand changes in the ocean as a result of climate change".

The study suggests that blue regions, such as the subtropics, will become even more blue, reflecting even less phytoplankton - and life in general - in those waters, compared with today. The subtropics-which include California, Texas and Florida-will become more blue, while areas near the poles, where warmer temperatures will lead to more diverse phytoplankton, will become greener.

The study reported in the journal Nature Communications said climate change was already changing the makeup of phytoplankton, and by extension, the colour of the oceans and the colour of the blue planet. "That basic pattern will still be there". Dutkiewicz is a principal research scientist at MIT's Department of Earth, Atmospheric, and Planetary Sciences and the Joint Program on the Science and Policy of Global Change.

The shades of the oceans' surfaces depend on how sunlight is interacting with what is in the water.

The molecules in water absorb all but the blue part of the spectrum of sunlight, and the water reflects that blue color back.

In total, climate change will alter at least 30 percent of the ocean's color by 2100 and perhaps more than 60 percent, the researchers say. If an ocean ecosystem were a building, phytoplankton represent one of the bricks at its foundation, supporting a vast array of life.

"Sunlight will come into the ocean, and anything that's in the ocean will absorb it, like chlorophyll", Dutkiewicz said.

The change in oceans' colour takes place because of the difference in quantities of phytoplankton, the microscopic algae that gives water bodies their distinct green colour. They consume carbon dioxide and release oxygen.

In other words, oceans that are rich in phytoplankton tend to look greener, whereas tropical waters with less phytoplankton take on an Instagram-worthy blue or turquoise hue.

But in the scientific world, they could mean significant shifts.

"Other things will absorb or scatter it, like something with a hard shell". That gets reflected back out, giving it its deep blue color. Scientists have predicted that if this continues, ocean colours would change by the end of the century.

They believe it will be 30-40 years before they can say for certain that climate change is having an impact on chlorophyll.

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. By the end of the century, our blue planet may look visibly altered.

"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.

"It could be potentially quite serious", Dutkiewicz added. 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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