"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", says lead author 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, in a statement. That's bad for climate change on several levels: For one, phytoplankton remove about as much carbon dioxide from the air as plants and help regulate our climate, research shows.
Writing in the journal Nature Communications, Hickman and colleagues from the United Kingdom and U.S. 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.
Phytoplankton, for instance, contain chlorophyll, a pigment which absorbs mostly in the blue portions of sunlight to produce carbon for photosynthesis, and less in the green portions.
The ocean is rich in diverse shades of blue and green.
"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. "Different types of phytoplankton absorb light differently, and if climate change shifts one community of phytoplankton to another, that will also change the types of food webs they can support", Dutkiewicz added. "That basic pattern will still be there". Likewise, the more abundant they are, the less blue the water will be.
To find out how much climate change will influence the ocean's color, the researchers built a model that simulates how ocean color will shift based on the amount and type of phytoplankton present.
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They found that increased heat will change the mixture of phytoplankton or tiny marine organisms in the seas, which absorb and reflect light. "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".
The molecules in water absorb all but the blue part of the spectrum of sunlight, and the water reflects that blue color back.
What the new hues will essentially reflect is life in those regions.
Satellites have been taking continuous measurements of the ocean's color since the late 1990s, the researchers noted. Any significant swings in chlorophyll could very well be due to global warming, but they could also be due to "natural variability" - normal, periodic upticks in chlorophyll due to natural, weather-related phenomena.
Scientists say there will be less of them in the waters in the decades to come. Dutkiewicz said those instruments will probably provide early signals of how climate change is altering the oceans and their colour. Under the assumption that climate change will continue at its expected rate throughout the 21st century, they then cranked up the ocean temperatures in their model by three degrees Celsius, which is what most scientists predict will happen under a scenario in which there's relatively no action taken to reduce greenhouse gases.
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", wrote Jennifer Chu in the press release.