New research suggests that small floating organisms that supply our world with up to one-fifth of their oxygen will be in an extreme situation as our oceans become more acidic.
Creatures, called diatoms, will be deprived of the building blocks of silica they need to build their protective shells, which have all sorts of dazzling opaline shapes.
Researchers have found that this could reduce their numbers by 26 percent by the end of the next century.
“Diatoms are one of the most important plankton groups in the ocean,” said marine biologist Jan Taucher of the GEOMAR Helmholtz Kiel Ocean Research Center (GEOMAR).
“Its decline could lead to a significant shift in the marine food web or even a shift to the ocean as a carbon sink.”
These unicellular algae make up 40 percent of the ocean’s photosynthetic biomass, making them one of the main components of the biological pump that removes CO2 from our atmosphere and stores it in the depths of the ocean. ocean.
They are one of the reasons why the oceans have managed to absorb much of the excess CO2 that humans have been producing.
(Samarpita Basu / Katherine RM Mackey / Wiki / CC BY-SA 4.0)
Above: The role of phytoplankton in the biological carbon pump.
But as our excess CO2 dissolves in seawater, it reacts to form more hydrogen ions, increasing the acidity of the water. This altered ocean chemistry has already caused a 10 percent decrease in carbonate concentrations since industrialization.
Less carbonate means it is more difficult for calcium carbonate to form; this is a vital molecule for most marine animals because it is part of their shells and exoskeletons.
If the carbonate concentration drops too low, the calcium carbonate dissolves. Some animals are now experiencing the dissolution of their shells.
Instead, it was thought that diatoms, which build their complex glass houses with completely different materials, would be relatively insensitive to ocean acidification, and possibly even benefit from CO2 increases.
These phytoplankton build their outer shells, called frustules, from silica floating in the surface waters of the ocean.
But new research identifies a factor that was lost in previous studies. It turns out that as the pH of the water drops, these vital silica blocks will begin to dissolve more slowly, which means that the deeper it sinks into the depths of the ocean before it becomes light enough to stay afloat. flotation.
This causes more silica at the bottom of the ocean, far from the reach of light-floating diatoms they use to convert CO2 into oxygen, water and carbohydrates, which impedes their ability to build. their furrowed dwellings.
Opal silica frustula with an increase of 1,500x. (Massimo Brizzi / Wikipedia / CC BY-SA 4.0)
Taucher and other researchers discovered this through giant oceanic “test tubes” (mesocosms), where they added different concentrations of CO2 to simulate future warming scenarios.
They then evaluated samples from different depths, analyzing the sediment full of dead diatoms they captured. This, along with modeling, supported by previous studies on the chemistry of diatom silica, revealed a surprising decrease in floating silica, suggesting that diatoms could shrink by about a quarter by about 2200.
Such a great loss of these phytoplankton will have drastic ramifications in the other life of our planet, since these organisms are one of the main primary producers of the ocean.
“[A]the associated consequences for the functioning of ecosystems and the carbon cycle are more difficult to assess, “the team said in its article, explaining that they did not take into account many physiological and ecological processes that can trigger a domino effect. rest of the food web.
Regardless, the findings show how the unexpected feedback mechanisms of Earth’s systems can drastically alter the environmental and biological changes we may think we understand, revealing that we still need to learn much more about how our planet and its forms intertwine. of life.
“This study once again highlights the complexity of the Earth’s system and the associated difficulty in predicting the consequences of man-made climate change as a whole,” says GEOMAR marine biologist Ulf Riebesell.
“Surprises like this remind us again and again of the incalculable risks we run if we do not counteract climate change quickly and decisively.”
This research was published in Nature.