Wednesday, 24 April, 2019

Rising temperatures to make oceans bluer and greener

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Sandy Nunez | 05 February, 2019, 14:27

Likewise, the more abundant they are, the less blue the water will be.

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. "That basic pattern will still be there".

"There will be a noticeable difference in the color of 50 percent of the ocean by the end of the 21st century", said Stephanie Dutkiewicz, 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.

Scientists already know that climate change is affecting plankton, with warmer waters leading to different algae species blooming in new waters, for instance. "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".

To make the distinction between greening due to climate change and due to isolated weather events or other factors, the researchers put in the measurements of reflected light from satellite imagery into a model that mapped oceanic currents and water mixing.

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.

They found that increased heat will change the mixture of phytoplankton or tiny marine organisms in the seas, which absorb and reflect light.

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.

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Ocean colour varies from green to blue, depending on the type and concentration of phytoplankton, or algae, in any given area. As a result, the simulation could show changes to the light being absorbed and reflected to the ocean based on the presence of phytoplankton.

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.

Dutkiewicz and her team built a climate model that projects changes to the oceans, including their optical properties, throughout the century.

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

A United Nations-backed panel of scientists said previous year that it will require "unprecedented" action over the coming decade for the world to limit warming and stave off the most catastrophic consequences of climate change. The sensors, which measure the colour of the water, work to calibrate satellite data in real time, providing information about the health of the Salish Sea. That gets reflected back out, giving it its deep blue color.

"The nice thing about this model is, we can use it as a laboratory, a place where we can experiment, to see how our planet is going to change", Dutkiewicz says.

As temperatures continue to rise, the numbers of these organisms in different locations will change causing a predicted 50% of the world's oceans to change colour.

For Mr. Strutton, "What this study has shown is that although the greenness of the oceans, the amount of chlorophyll might only be changing by small amounts, what's important is that the type of phytoplankton might be changing more dramatically". "It could be potentially quite serious".