ocean color
Ecology

Change of color of the ocean, climate emergency
10/07/2019

By the end of the century, the mosaic of blues and greens of the oceans could change. This is revealed by a new study published in "Nature communications".


Why is the ocean changing color?


Sunlight penetrates more than 180 meters below the surface of the ocean. Everything beyond that is plunged into darkness. On the surface, the majority of water molecules are able to absorb all colors except blue. This is the reason why the ocean is of this color. When organisms are present in the water, they can absorb or reflect different wavelengths. Thus, marine phytoplankton contain chlorophyll, a pigment that absorbs more radiation in the blue color to achieve photosynthesis, and less in the green. This is why surface waters rich in microscopic algae appear greener.

For the past twenty years, satellites have been taking measurements of the color of the oceans. Satellites provide, among other things, information on chlorophyll, and thus on phytoplankton present in different oceanic regions. This one is in great danger. Indeed, global warming is causing changes in the production and composition of plankton. Natural phenomena such as El Niño and El Niña also come into play.

Researchers at the Massachusetts Institute of Technology (MIT) have developed a model to simulate the growth of different phytoplankton species based on temperature variations. They also predicted how phytoplankton absorb and reflect light, and therefore the color that surface water should take. They were able to conduct the experiment with the results provided by the satellites. The researchers, led by Stephanie Dutkiewicz, simulated a temperature increase of 3°C by 2100. This scenario is plausible if greenhouse gas emissions do not decrease. According to scientists, more than 50% of ocean waters will change color due to climate change. In the subtropics, warm waters would become bluer due to reduced phytoplankton and marine life in general. Other regions are expected to grow in green, closer to the poles, as phytoplankton could become more abundant and more diverse. This change, however, should not be visible to the eye.


Importance of phytoplankton


Phytoplankton is the base of the marine food chain. Indeed, if there is no more phytoplankton, there will be no zooplankton, no fish, no marine animals and so on. It produces half of the oxygen we breathe. It is also the source of our precious oil. It interacts with the local and global climate by intervening in the carbon cycle via photosynthesis. but also, by emitting after its death sulfur molecules that contribute to the nucleation of water vapor into raindrops, that is to say to the formation of clouds and precipitations and by displacing this carbon in the column of water.


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