Ocean about to release its CO2 reserves

Ocean about to release its CO2 reserves
Ocean about to release its CO2 reserves

The ocean absorbs about a third of our carbon dioxide (CO) emissions2)). And it is not without consequences. As we continue to burn fuelsfuels fossils, our ocean is becoming acidic. The threat to ecosystems is real. So while the ocean may seem like a fabulous carbon sink, perhaps we shouldn’t rely too much on it to limit anthropogenic global warming.

Will the ocean continue to store carbon?

Yet this is one of the invaluable services that the ocean provides us today. Even if with the changes underway, it is beginning to absorb less CO2 from the atmosphere, scientists estimate that it also releases a little less. As a result, it continues to be a valuable help to us for the time being. But this may not last much longer. Researchers from the Massachusetts Institute of Technology (MIT, United States) have just made an unexpected discovery on this subject. In the journal Nature Communicationsthey reveal that as ocean circulation slows down – one of the observed effects of global warming – the ocean could start to release more and more carbon previously trapped in the depths.

“What we thought was happening in the ocean has been completely turned upside down. notes Jonathan Lauderdale, a researcher in the Department of Health Sciences, TerreTerreatmosphere and planets, in a press release from MIT. We cannot rely on the ocean to store our carbon. We must be proactive in reducing emissionsemissions now, rather than relying on these natural processes to give us time to mitigate climate change.”

Phytoplankton to absorb CO2 from the atmosphere

To understand, we must go back to 2020. MIT researchers then developed a model of“boxes”which represented different parts of the ocean with a different balance of nutrientsnutrientsof ferfer and those they call ligandsligandsof the moleculesmolecules organic matter considered to be byproducts of phytoplankton. By then modeling a flow between these boxes, the researchers concluded that even with additional iron added to the ocean, the growth of phytoplanktonphytoplankton would not be better.

But why do we want to boost the growth of phytoplankton? Because when it grows, it absorbs CO2 from the atmosphere by photosynthesisphotosynthesisIts role in the ocean’s capacity to store carbon is therefore crucial.

Geoengineering: Seeding the ocean with iron won’t help limit global warming

In summary, what scientists explained four years ago is that, without a ligand, iron is not really available to phytoplankton. It therefore does not take advantage of this to absorb more CO2 of the atmosphere. And today, after having completed their models by including ocean/atmosphere exchanges, researchers are discovering an even worse situation.

Towards a CO2-emitting ocean?

“The result was so surprising that I thought I had made a mistake”says Jonathan Lauderdale. His model indicated that when ligand concentrations vary from one region of the ocean to another, then the weaker the ocean circulation, the more CO2 accumulates in the atmosphere. The trouble is, it turns out that in the real world, ligand concentrations do indeed change from one region of the ocean to another.

The researchers explain. As ocean circulation slows down due to global warming, the ocean extracts less carbon and nutrients from its depths. As a result, surface phytoplankton lacks resources. It then produces fewer ligands. And fewer ligands also mean less available iron and therefore… fewer phytoplankton to absorb CO2 of the atmosphere. All in what scientists call a feedback loopfeedback loop. More commonly, a vicious circle.

” Some climate modelsclimate models predict a 30% slowdown in ocean circulation due to the sourcesource of the ice capsice capsparticularly around theAntarcticAntarcticThis huge slowdown in circulation could become a big problem: in addition to a host of other climate problems, not only would the ocean absorb less CO2 anthropogenic atmospheric pollution, but this could be amplified by a degassingdegassing net deep ocean carbon leading to unexpected increase in CO2 atmospheric and further global warming”concludes Jonathan Lauderdale.

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