The impact of global warming on phytoplankton will change the color of the ocean surface more quickly than originally thought, a new US study concludes.
The color of the ocean is based on the interaction between sunlight and water, which absorbs the rays and reflects the blue part of the spectrum. The presence of organisms in the water changes the way the light is absorbed.
Phytoplankton, for example, contains chlorophyll, a pigment that absorbs the blue of light during photosynthesis. Areas denser in phytoplankton therefore have a greenish tint.
Researchers at the Massachusetts Institute of Technology (MIT) simulated the impact that warming would have on phytoplankton, and then calculated how it would absorb and then reflect light.
“There will be a noticeable difference in the color of 50% of the ocean by the end of the 21st century,” says Stephanie Dutkiewicz, lead author of the study published in Nature Communications (New Window) .
It will be difficult to perceive this change of color with the naked eye. The satellite images will show, however, that the blue and green of the planet’s oceans will become darker.
An improved model
To understand the effects of climate change, scientists generally rely on the concentration of chlorophyll in the ocean.
“We use satellite data that measure the color of the water, and then we use algorithms to deduce the concentration of chlorophyll,” says Claudie Beaulieu, a researcher from Quebec who co-signed the study.
“The MIT model allows you to compare the reflectance directly,” says one who recently joined the Ocean Science Department team at the University of California at Santa Cruz.
What we see is that climate change is happening a little faster if you look at the color of the water, rather than the chlorophyll concentration alone.
“This is an interesting result, since it gives us a precursor to the impact of climate change on the primary productivity of the oceans,” she continues.
Impact on the underwater ecosystem
More than 70% of the Earth’s surface is covered with oceans.
The increase in water temperature affects the growth rate of organisms, such as phytoplankton, and disrupts ocean currents. Regions will be richer in phytoplankton and others, poorer.
“If there are changes in the abundance and composition of phytoplankton communities, we can expect that there will be repercussions in the rest of the ocean food chain,” says Claudie Beaulieu.
Phytoplankton is at the base of the food chain. These changes will affect small fish, invertebrates, and so on.
Another impact, she continues, is the “service that [phytoplankton] makes us absorb CO2”. Like plants on Earth, plants in the ocean absorb carbon dioxide.
The study was based on a rise in global temperatures of 3 ° C by 2100, which is predicted by most scientists at the current rate of greenhouse gas emissions.