By the end of the 21st century, most of the oceans will change color

Climate change is a significant change in the state of phytoplankton in the oceans, and a new study MIT showed that in the coming decades, these changes have a major impact on ocean color, enhancing its blue and green areas. The satellites should detect these changes in hue and early warning of large-scale changes in marine ecosystems.

By the end of the 21st century, most of the oceans will change color

in the journal Nature Communications, scientists report that developed a global model that simulates the growth and interaction of different types of phytoplankton or algae, as well as how the mixture of species in different locations will change when the temperature rises around the world. The researchers also modeled as phytoplankton absorbs and reflects light, and how the color of the ocean because of global warming affects the composition of phytoplankton communities.

The researchers tested their model, scroll to the end of the 21st century, and found that by 2100 more than 50% of the world's oceans has changed its color, due to climate change.

Research suggests that the blue areas, such as the subtropics, will become even more blue, because the phytoplankton will be less - and life in general - in these waters, when compared with the current status. Some regions that are now more green, such as those near the poles can become even greener, since higher temperatures lead to the spread of various phytoplankton ..

"This model implies that the naked eye, these changes will be noticed is not easy, and the ocean will still look as if it has a blue field in the subtropics and more green - near the equator and the poles," says lead author Stephanie Datkevich of the Department of earth, atmospheric and Planetary MIT. "This basic pattern remains the same. However, profound changes are significant enough to affect the rest of the food chain, which is based on phytoplankton. "

The color of the oceans depends on the amount of chlorophyll

The color of the ocean depends on how sunlight interacts with what is in the water. Only water molecules absorb almost all of the sunlight, except for the blue part of the spectrum - it is reflected. Consequently, relatively barren area of ​​open ocean seem dark blue from space. If the ocean there are any organisms, they can absorb and reflect light waves of different lengths, depending on their individual properties.

Phytoplankton, for example, contains chlorophyll pigment that absorbs mainly blue portions of sunlight, producing carbon in photosynthesis, and to a lesser extent - the green parts. As a result, more green light is reflected from the ocean, which makes the area rich in algae, a greenish tint.

Since the late 1990s, satellites constantly measured ocean color. Scientists have used these measurements to produce chlorophyll and therefore phytoplankton in a particular area of ​​the ocean. But Datkevich says that chlorophyll does not necessarily reflect the sensor signal of climate change. Any significant variations in chlorophyll may well be caused by global warming, but also - "natural variability" normal periodic jumps in chlorophyll due to natural phenomena associated with the weather.

"Event level of El Niño or La Niña will cause very large changes in chlorophyll, because it changes the amount of nutrients entering the system," says Datkevich. "Because of these large, natural changes that occur every few years, it is difficult to understand whether the situation will change because of climate change, if we just look at the chlorophyll."

Simulation of ocean light

Instead of looking at the estimates of chlorophyll, the team wondered whether it is possible to see a clear signal about the impact of climate change on phytoplankton, if you look only at satellite measurements of the reflected light.

Group finalized a computer model, which was used in the past to predict phytoplankton changes at higher temperatures and ocean acidification. This model takes information on phytoplankton, such as its consumption of food, and as it grows, and include this information in a physical model, which shows the ocean currents and mixing.

This time, however, the scientists added a new element of the model, which was not included in other ocean modeling techniques: the ability to assess the specific wavelengths of light that are absorbed and reflected the ocean, depending on the number and type of organisms of a given region.

"Sunlight falls into the ocean, and all that is in the ocean absorbs it as chlorophyll," says Datkevich. "Other things are going to absorb it and dissipate. So determine how light will be reflected from the ocean and give it color, hard enough.

It turned out that scientists model can be used to predict ocean color when environmental conditions change in the future. And the best thing about this is that it can be used in the laboratory.

The signal in the blue-green colors

When the researchers added a model of global temperatures and increased them by 3 degrees by 2100 - this is the forecast of most scientists, if any action to reduce greenhouse gas emissions will not be taken - they found the wavelengths of light in the blue and green portions of the spectrum have reacted fastest . Moreover, the blue-green wavelength range shows a very clear signal, or shift due to climate change: the shift occurs sooner than expected, when the researchers looked at the chlorophyll.

"Chlorophyll is changing, but you can not see it because of the incredible natural variability," said Datkevich. "However, you can see significant climate change in some of these wave bands in the signal that is sent to the satellites. So this is where we should look for a real change in the signal of satellite measurements. "

According to the model of scientists, climate change is already changing the composition of phytoplankton, and hence the color of the oceans. By the end of the century, our blue planet will change much.

"By the end of the 21st century will be a noticeable change in color of 50% of the oceans. The change will be quite serious. Different types of phytoplankton in different ways to absorb light, and if climate change will displace one another phytoplankton community, it will also change the types of food chains that they can support. "

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