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

Climate change causes significant changes.in the state of phytoplankton in the oceans, and a new MIT study showed that in the coming decades these changes will greatly affect the color of the ocean, intensifying its blue and green areas. Satellites should detect these changes in shade and warn in advance of large-scale changes in marine ecosystems.

In the journal Nature Communications, scientists reportthat they have developed a global model that mimics the growth and interaction of different phytoplankton species, or algae, and how the mixture of species in different places will change with increasing temperature around the world. The researchers also modeled how phytoplankton absorbs and reflects light, and how the color of the ocean changes as global warming affects the composition of phytoplankton communities.

The researchers tested their model, rolling it through to the end of the 21st century, and found that by 2100 more than 50% of the world's oceans would change their color due to climate change.

The study suggests that the blue areassuch as subtropics, will become even bluer, since phytoplankton will be less - and life in general - in these waters, when compared with the current state of affairs. Some regions that are greener today, such as those near the poles, may become even greener, as higher temperatures lead to the spread of diverse phytoplankton ..

"This model assumes that the unarmedThis change will not be easy to see, and the ocean will still look as if it has blue areas in the subtropics and greener areas near the equator and the poles, ”says lead author Stephanie Datkevich from the Department of Earth Science Institute. “This basic scheme will remain the same. However, the deep changes will be significant enough to affect the rest of the food chain, which rests on phytoplankton. "

The color of the oceans depends on the amount of chlorophyll.

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

Phytoplankton, for example, contains chlorophyll,a pigment that absorbs mostly blue patches of sunlight, producing carbon for photosynthesis, and to a lesser extent green parts. As a result, more green light reflects off the ocean, which gives algae-rich areas a greenish tint.

Since the late 1990s, satellites have continuously measuredthe color of the ocean. Scientists have used these measurements to obtain the amount of chlorophyll and, accordingly, phytoplankton in a specific area of ​​the ocean. But Datkevich says that chlorophyll will not necessarily reflect a sensitive signal of climate change. Any significant fluctuations in chlorophyll may well be caused by global warming, but also by “natural variability”, normal periodic jumps in chlorophyll due to natural weather-related phenomena.

"An El Nino or La Nina Event will triggervery 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 you just look at chlorophyll."

Modeling Ocean Light

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

The group refined the computer model, whichused in the past to predict phytoplankton changes with rising temperatures and ocean acidification. This model takes information about phytoplankton, such as its food consumption, and how it grows, and incorporates this information into a physical model that demonstrates ocean currents and mixing.

This time, however, the scientists added to the modelA new element that was not included in other methods of modeling the ocean: the ability to estimate specific wavelengths of light that are absorbed and reflected by the ocean, depending on the number and type of organisms in a particular region.

"Sunlight hits the ocean, and all thatis in the ocean, absorbs it like chlorophyll, ”says Datkevich. “Other things will absorb it or dissipate it. So to determine how light will be reflected from the ocean and give it color is difficult enough.

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

Signal in blue-green tones

When scientists added global to the modeltemperatures and increased them by 3 degrees by 2100 - this is the forecast of most scientists, if no action is taken to reduce greenhouse gas emissions - they found that the wavelengths of light in the blue and green parts of the spectrum responded the fastest.

Moreover, this blue-green wavelength rangedemonstrates a very clear signal, or shift, associated with climate change: the shift occurs earlier than expected when scientists looked at chlorophyll.

"Chlorophyll is changing, but you can't see itbecause of the incredible natural variability, "says Datkevich. “However, you can see significant climate change in some of these wavelengths in the signal sent to the satellites. So it is here that we should look for a real signal of changes in satellite measurements. ”

According to 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 dramatically.

"By the end of the 21st century, there will be a change in color50% of the oceans. The change will be pretty serious. Different phytoplankton types absorb light differently, and if climate change shifts one phytoplankton community to another, it will also change the types of food chains that they can sustain. ”

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