Seas will change colour as climate heats up

  • Seas will change colour as climate heats up

Seas will change colour as climate heats up

Areas in the subtropics, including much of the Atlantic Ocean, will become bluer, whereas regions near the poles will become greener thanks to shifts in the types and abundance of different kinds of phytoplankton, the team reports today in the journal Nature Communications.

Writing in the journal Nature Communications, Hickman and colleagues from the United Kingdom and USA report how they came to their conclusions by using a computer model that predicts how factors such as temperature, ocean currents and ocean acidity affects the growth and types of phytoplankton in the water, as well as levels of other coloured organic matter and detritus.

According to the researchers, the ocean will see its blue and green regions intensify so much so that satellite imaging will detect these the new hues.

"There will be a noticeable difference in the color of 50 percent of the ocean by the end of the 21st century", Dutkiewicz said in a statement. They also simulated how phytoplankton absorbs and reflects light, learning that climate change will effectively alter the ocean's coloring near the surface. "That basic pattern will still be there".

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. They're able to do this because water absorbs most sunlight with the exception of blue parts of the spectrum, which is reflected back out.

At the heart of the phenomenon lie tiny marine microorganisms called phytoplankton, which are crucial to ocean food webs and to the global cycling of carbon - and sensitive to the temperature of ocean waters. According to Pete Strutton, an Associate Professor at the Institute for Marine and Antarctic Studies at the University of Tasmania, "Phytoplankton produce half of the oxygen in the earth's atmosphere and are at the very base of the food chain".

"Looking at just the colour of the ocean, and how that is going to change in the future by monitoring it from satellites, is actually going to give us an early warning signal of changes in the phytoplankton", said Hickman. As a result, more green light is reflected back out of the ocean, giving algae-rich regions a greenish hue.

One way to monitor changes on a global scale is through observing the color of the ocean satellite data. The phytoplankton that live in the sunlit part of the ocean are hugely important, as they serve as the base of the marine food web.

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

"What we've shown is that the colour in the blue-green range is going to show that signal of change sooner, in some places in maybe the next decade", said Dr Dutkiewicz.

Scientists already know that climate change is affecting plankton, with warmer waters leading to different algae species blooming in new waters, for instance. Their model can estimate wavelengths of light that are absorbed and reflected by the ocean, which obviously changes by a given region and the organisms in the water.

As the researchers cranked up global temperatures in the model, by up to 3 degrees Celsius by 2100 - what most scientists predict will occur under a business-as-usual scenario of relatively no action to reduce greenhouse gases - they found that wavelengths of light in the blue/green waveband responded the fastest. "But they're important because they tell us a lot about what's changing in the ocean". "By the end of the century, our blue planet may look visibly altered", wrote Jennifer Chu in the press release.