The tiny floating organisms that feed our world up to a fifth of its oxygen will be in dire straits as our oceans acidify, according to new research.
The creatures, called diatoms, will be deprived of the silica building blocks they need to build their protective shells, which come in all sorts of dazzling opaline forms.
This could reduce their numbers by up to 26% by the end of the next century, researchers have found.
“Diatoms are one of the most important groups of plankton in the ocean”, Explain marine biologist Jan Taucher of the GEOMAR Helmholtz Center for Ocean Research Kiel (GEOMAR).
“Their decline could result in a significant change to the marine food web or even a change to the ocean as a carbon sink.”
These single-celled algae make up 40% of the photosynthetic biomass of the ocean, making them one of the main components of biological pump who takes CO2 out of our atmosphere, storing it in the depths of the ocean.
They are one of the reasons the oceans have succeeded take a chunk excess CO2 we humans produce.
Above: 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 led to a 10% decrease in carbonate concentrations since industrialization.
Less carbonate means it is harder for calcium carbonate to form; it is a vital molecule for most marine animals as it is part of their shells and exoskeletons.
If the carbonate concentration drops too low, the calcium carbonate dissolves. Some animals now know the dissolution of their shells.
In contrast, diatoms, which build their complex glass houses out of completely different materials, were thought to be relatively immune to ocean acidification, and may even benefit from increases in CO2.
These phytoplanktons build their outer shells, called frustulessilica that floats in the surface waters of the ocean.
But the new research identifies a factor that has been missed by previous studies. It turns out that as the pH of the water drops, these vital silica elements will start to dissolve more slowly, which means more of it will sink deeper into the depths of the ocean. before it becomes light enough to stay afloat.
This leads to more silica at the bottom of the ocean, well out of reach of diatoms floating in the light which they use to transform CO2 in oxygen, water and carbohydrates, which hinders their ability to build their frustule homes.
Taucher and his fellow researchers discovered it using giant ocean “test tubes” (mesocosms), where they added different concentrations of CO2 to simulate future warming scenarios.
They then assessed samples from different depths – analyzing the sediments filled with dead diatoms that they captured. This, together with modeling, supported by previous studies on diatom and silica chemistryrevealed a staggering decline in floating silica, suggesting that diatoms could decline by up to about a quarter by 2200.
Such a huge loss of these phytoplankton will have dramatic ramifications for other life forms on our planet, given that these organisms are one of the main primary producers.
“[A]The associated consequences on ecosystem functioning and the carbon cycle are more difficult to assess,” the team said. states in his articleexplaining that they did not take into account many physiological and ecological processes that could trigger a domino effect on the rest of the food web.
Either way, the results show how unexpected feedback mechanisms in Earth systems can radically alter environmental and biological changes that we may think we understand – revealing that we still have a lot to learn about how our planet works. and its life forms are intertwined.
“This study highlights once again the complexity of the Earth system and the associated difficulty in predicting the consequences of climate change in its entirety,” said GEOMAR marine biologist Ulf Riebesell.
“Surprises like this remind us again 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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