(ORDO NEWS) — The tiny swimming organisms that provide our world with a fifth of the oxygen will be in dire straits when the oceans become acidic, new research shows.
These creatures, called diatoms, will be deprived of the silica needed to build their protective shells, which come in a variety of dazzling opal shapes.
This could lead to a 26 percent reduction in their numbers by the end of the next century, the researchers say.
“Diatoms are one of the most important groups of plankton in the ocean,” explains marine biologist Jan Taucher from the Helmholtz Center for Ocean Research in Kiel (GEOMAR).
“Their decline could lead to significant changes in the marine food web, or even a change in the role of the ocean as a carbon sink.”
These single-celled algae make up 40 percent of the ocean’s photosynthetic biomass, making them one of the main components of the biological pump that draws CO2 from our atmosphere and stores it in the deep ocean.
They are one of the reasons why the oceans have been able to absorb a huge chunk of the excess CO2 that we humans produce.
But when excess CO2 dissolves in seawater, it reacts to form more hydrogen ions, making the water more acidic. This change in ocean chemistry has already resulted in a 10 percent decline in carbonate concentrations since industrialization.
Less carbonate means it’s harder for calcium carbonate to form; it is a vital molecule for most marine animals as it forms part of their shells and exoskeletons.
If the carbonate concentration falls too low, the calcium carbonate dissolves. Some animals are currently experiencing the dissolution of their shells.
In contrast, it was thought that diatoms, which build their intricate glass houses from completely different materials, would be relatively immune to ocean acidification and might even benefit from rising CO2 levels.
These phytoplankton build their outer shells, called frustules, from silica that floats in the surface waters of the ocean.
But the new study uncovered a factor that had been overlooked by previous studies. It turns out that as the pH of the water drops, these vital building blocks of silica begin to dissolve more slowly, meaning that more and more of them sink into the deep ocean before they are light enough to stay afloat.
This results in more silica on the ocean floor, unavailable to diatoms floating in light, which they use to convert CO2 into oxygen, water and carbohydrates, hindering their ability to build their frustula homes.
Taucher and other researchers discovered this by using giant ocean “test tubes” (mesocosms) that were spiked with varying concentrations of CO2 to simulate future warming scenarios.
They then assessed samples from different depths, analyzing sediments filled with dead diatoms. This, along with modeling backed up by previous studies of diatom silica chemistry, showed a staggering reduction in floating silica, suggesting that diatom numbers could drop by a quarter by the year 2200.
Such a huge loss of phytoplankton would have drastic consequences for other life on our planet, as these organisms are among the ocean’s major primary producers.
“The associated implications for ecosystem function and carbon cycling are more difficult to assess,” the team said in the paper, explaining that they had not accounted for many of the physiological and ecological processes that could cause a domino effect on the rest of the food web.
However, the results of the study show how unexpected feedback mechanisms in the Earth‘s systems can radically change the ecological and biological changes we think we understand and show that we still have a lot to learn about how our planet and Earth are intertwined. her life form.
“This study once again highlights the complexity of the Earth system and the associated difficulty in predicting the impacts of anthropogenic climate change in its entirety,” says GEOMAR marine biologist Ulf Ribesell.
“Surprises like these remind us again and again of the incalculable risks we face if we don’t act quickly and decisively on climate change.”
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