Published: Tue, February 05, 2019
Sci-tech | By April Francis

Rising temperatures to make oceans bluer and greener

Rising temperatures to make oceans bluer and greener

Areas that are predominantly blue, such as the subtropics, will become even more blue as phytoplankton - and all the life it supports, which is virtually all life in the area - dwindle. When there is too little, the quantity of life in the waters goes down and water's natural blue comes through. Thus, more quantity of phytoplankton, lesser the blue color in the sea and more of green shaded water.

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

"The model suggests the changes won't appear huge to the naked eye, and the ocean will still look like it has blue regions in the subtropics and greener regions near the equator and poles", lead study author Stephanie Dutkiewicz, a planetary scientist at MIT, told MIT News.

They also play an important role in how we see the oceans with our eyes. However, in an important twist to previous studies, they also explored how such changes would affect the absorption and reflection of light at the ocean surface. "If they were to magically change - or if we were to kill them off completely - there would be a lot of carbon coming out of the ocean and back into the atmosphere, and creating more problems that we have now". Climate change is altering the ocean currents, meaning there will be fewer nutrients for phytoplankton to feed on in some areas, so there will be a decline in their number in those regions.

For the study, the researchers developed a global model that simulates the growth and interaction of different species of phytoplankton. "We are interested in phytoplankton because they are tiny marine plants, they contribute about half of global photosynthesis, they are the base of the marine food web". Because they contain a pigment that reflects green light, portions of sunlight that bounces back make the water glow with a greenish hue.

Based on this principle, scientists have been using satellites to measure ocean color since the late 1990s. Those levels can change because of weather events or because of climate change.

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. It has been predicted that North Atlantic ocean will top the list in reflecting this change followed by Southern Ocean. If there are any organisms in the ocean, they can absorb and reflect different wavelengths of light, depending on their individual properties. "But you can see a significant, climate-related shift in some of these wavebands, in the signal being sent out to the satellites".

The team, which includes researchers from MIT, University of Southhampton, National Oceanography Centre Southampton, University of California at Santa Cruz, and University of California at Davis, states that the new model shows that the effects of climate change on the oceans is far more rapid than expected. Different hues of chlorophyll absorb different wavelenghts of light, and such climate-induced changes could have a dramatic impact on the ocean's food webs, the team concludes.

What's more, Dutkiewicz observed that this blue/green waveband showed a very clear signal, or shift, due specifically to climate change, taking place much earlier than what scientists have previously found when they looked to chlorophyll, which they projected would exhibit a climate-driven change by 2055.

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