Much of the surface ocean will shift in color by end of 21st century

Climate-driven changes in phytoplankton communities will intensify the blue and green regions of the world’s oceans.


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The Earth’s climate has changed throughout history. Just in the last 650,000 years, there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 7,000 years ago marking the beginning of the modern climate era — and of human civilization.

Most of these climate changes are attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives.

In a new study by the MIT scientists, suggests that this climate change leads to phytoplankton in the world’s oceans. Scientists predicted that the changes will affect the ocean’s color, intensifying its blue regions and its green ones.

During the study, scientists developed a model that reproduces the growth and cooperation of various types of phytoplankton, or algae, and how the blend of species in different areas will change as temperatures ascend the world over. The scientists additionally recreated the way in which phytoplankton retain and reflect light, and how the oceans’ color changes as global warming influence the makeup of phytoplankton networks.

The researchers ran the model through the end of the 21st century and found that, by the year 2100, more than 50 percent of the world’s oceans will shift in color, due to climate change.

The study suggests that blue regions, such as the subtropics, will become even more blue, reflecting even less phytoplankton — and life in general — in those waters, compared with today. Some regions that are greener today, such as near the poles, may turn even deeper green, as warmer temperatures brew up larger blooms of more diverse phytoplankton.

Lead author Stephanie Dutkiewicz, a principal research scientist at MIT’s Department of Earth, Atmospheric, and Planetary Sciences said, “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.”

“That basic pattern will still be there. But it’ll be enough different that it will affect the rest of the food web that phytoplankton supports.”

Rather than hoping to derived estimates of chlorophyll, the group pondered whether they could see a reasonable flag of environmental change’s impact on phytoplankton by taking a gander at satellite estimations of reflected light alone.

Scientists then changed a computer model show that it has utilized in the past to anticipate phytoplankton changes with rising temperatures and ocean acidification. This model takes data about phytoplankton, for example, what they devour and how they develop and fuses this data into a physical model that mimics the ocean’s currents and mixing.

This time around, the researchers added a new element to the model, that has not been included in other ocean modeling techniques: the ability to estimate the specific wavelengths of light that are absorbed and reflected by the ocean, depending on the amount and type of organisms in a given region.

Dutkiewicz said, “Sunlight will come into the ocean, and anything that’s in the ocean will absorb it, like chlorophyll. Other things will absorb or scatter it, like something with a hard shell. So it’s a complicated process, how light is reflected back out of the ocean to give it its color.”

Comparing the results scientists found that they found the two agreed well enough that the model could be used to predict the ocean’s color as environmental conditions change in the future.

analysts cracked up worldwide temperatures in the model, by up to 3 degrees Celsius by 2100 — what most scientists foresee will happen under a business-as-usual situation of moderately no activity to lessen ozone-harming substances — they found that wavelengths of light in the blue/green waveband reacted the quickest.

Scientists observed that this blue/green waveband showed a very clear signal, or shift, due specifically to climate change, taking place much earlier than what scientists have previously found when they looked to chlorophyll, which they projected would exhibit a climate-driven change by 2055.

Dutkiewicz said, “Chlorophyll is changing, but you can’t really see it because of its incredible natural variability. But you can see a significant, climate-related shift in some of these wavebands, in the signal being sent out to the satellites. So that’s where we should be looking in satellite measurements, for a real signal of change.”

According to their model, climate change is already changing the makeup of phytoplankton, and by extension, the color of the oceans. By the end of the century, our blue planet may look visibly altered.

The study is published in the journal Nature Communications.


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