Acidic Oceans Could Dramatically Reduce One of the World’s Largest Oxygen Producers

The tiny floating organisms that supply our world with no less than a fifth of his oxygen will be in heavy weather like our oceans acidifynew research suggests.

The creatures, called diatoms, will be robbed of the silica building blocks they need to build their protective shells, which come in all sorts of dazzling opaline shapes.

This could reduce their numbers by 26 percent by the end of the next century, researchers have found.

“Diatomas are one of the most important plankton groups in the ocean,” explains marine biologist Jan Taucher of the GEOMAR Helmholtz Center for Ocean Research Kiel (GEOMAR).

“Their decline could lead to a significant shift in the marine food web or even a change for 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 major components of the biological pump that costs CO2 from our atmosphere and stores it in the depths of the ocean.

They are one of the reasons the oceans have succeeded absorb a huge chunk of the excess CO2 we humans have produced.

(Samarpita Basu/Katherine RM Mackey/Wiki/CC BY-SA 4.0)

Above: The role of phytoplankton in the biological carbon pump.

But because our excess CO2 dissolves in seawater, it reacts to form more hydrogen ions, which increases the acidity of the water. This altered ocean chemistry has already led to a 10 percent decrease in carbonate concentrations since industrialization.

Less carbonate means it is more difficult for calcium carbonate to form; this is an essential molecule for most marine animals as it is part of their shells and exoskeletons.

If the concentration of carbonate becomes too low, calcium carbonate dissolves. Some animals are now experiencing the dissolving their shells

By contrast, diatoms, which build their intricate greenhouses from completely different materials, were thought to be relatively impervious to ocean acidification, and may even benefit from the rise in CO2

This phytoplankton forms their outer shell, called frustulesfrom the silica floating in the surface water of the ocean.

But the new research identifies a factor that missed by previous studies† It turns out that as the pH of the water drops, these vital silica building blocks begin to dissolve more slowly, meaning more of them will sink further into the ocean depths before it gets light enough to float.

This leads to more silica on the ocean floor, well beyond the reach of the diatoms floating in the light they use to absorb CO.2 converted to oxygen, water and carbohydrates, hindering their ability to build their frugal homes.

Incredible detail of an opalized silica frustule under 1500x magnification.An opaline silica frustule under 1,500x magnification. (Massimo brizzi/Wikipedia/CC BY-SA 4.0)

Taucher and fellow researchers discovered this using giant oceanic “test tubes” (mesocosm), where they have different concentrations of CO. have added2 to simulate future warming scenarios.

They then evaluated samples from various depths and analyzed the dead diatom-filled sediment they captured. This, along with modeling supported by previous studies on diatomaceous silica chemistryrevealed a staggering decline in floating silica, suggesting that diatoms could decline by about a quarter by 2200.

Such a massive loss of this phytoplankton will have drastic consequences for other life on our planet, as these organisms are one of the most important primary producers

†[A]Associated impacts on ecosystem functioning and carbon cycles are more difficult to estimate,” the team said is in their newspaperand explained that they were not responsible for many physiological and ecological processes that can cause a knock-on effect on the rest of the food web.

Either way, the findings show how unexpected feedback mechanisms in Earth’s systems can dramatically alter the ecological and biological changes we might think we understand — revealing that there is so much more we need to learn about how our planet and its life forms are intertwined.

“This study once again highlights the complexity of the Earth system and the associated difficulty in predicting the impacts of man-made climate change in its entirety,” say GEOMAR marine biologist Ulf Riebesell.

“Surprises like these remind us time and again of the incalculable risks we face if we don’t tackle climate change quickly and decisively.”

This research was published in Nature

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