A new study recently published in The ISME magazine has revealed that diazotrophs, a group of marine cyanobacteria that contain nitrogen gas (N2) from the atmosphere to nutrients for primary producers in the ocean, contribute directly to carbon export and sequestration on the seafloor.
The results of this work led by the French Mediterranean Institute of Oceanography (MIO), conducted as part of the TONGA Ocean Expedition, represent a major paradigm shift, as these microorganisms were previously known to2 captured from the atmosphere, but the experts didn’t know they could also capture the CO2 with them as they die and sink, just like the rest of the phytoplankton (i.e. plant plankton).
“This process is known as the biological carbon pump and until now has been mainly attributed to phytoplankton, which convert CO2 converted to organic matter during photosynthesis. When it dies, the carbon sinks with these microorganisms and stores about twice as much carbon on the seafloor as is currently found in the atmosphere,” explains Francisco Cornejo, researcher at the Institut de Ciències del Mar (ICM-CSIC) and one of the authors of the study.
In turn, organisms at higher levels of the marine food web use the same organic matter for survival, ensuring the functioning of the entire oceanic system. Thanks to the biological carbon pump, the ocean is even considered a carbon sink.
Shifting the paradigm
The results of the now published study have important implications for science, because at present global biogeochemical models (i.e. the tools used to make predictions about the evolution and fluxes of carbon on the planet) do not take into account the direct contribution of diazotrophs in this process.
“Our results will give us a more accurate picture of ocean carbon flows, which is especially relevant at a time when climate models predict an expansion of nitrogen-poor zones, where diazotrophs thrive,” said MIO researcher Sophie Bonnet, who initiated this joint study. .
To conduct their research, researchers collected hundreds of sediment trap samples installed at various depths during a South Pacific campaign, which were later analyzed using microscopy, sequencing and DNA quantification techniques.
Because of this, they noticed that the particles that sink from the surface to the sea floor, in addition to phytoplankton organisms, contain a large amount and diversity of these diazotrophs. All this has made it possible for the first time to quantify the role of these microorganisms in the global biological carbon pump.
For future research, experts will try to dig deeper into the role of diazotrophs in the biological carbon pump, with special focus on the pathways these microorganisms undergo during their sinking in the different oceanic regions.
The seasonality of oceanic carbon cycles
Sophie Bonnet et al, Diazotrophs are overlooked as contributing to the export of carbon and nitrogen to the deep ocean, The ISME magazine (2022). DOI: 10.1038/s41396-022-01319-3
Provided by Institut de Ciències del Mar (ICM-CSIC)
Quote: Diazotrophs are overlooked as contributing to the export of carbon and nitrogen to the deep ocean (2022, October 17) retrieved October 17, 2022 from https://phys.org/news/2022-10-diazotrophs-overlooked- contributors-carbon-nitrogen.html
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