Major algae study reveals ocean carbon cycle is not what previously thought

Did you know diatoms? They make up a large part of phytoplankton, or “phytoplankton.” Not only do these single-celled algae play an essential role in the ocean by absorbing carbon dioxide dissolved in the water and converting it into organic matter using energy from the sun, they also turn into… incredibly beautiful!

Depending on the species, their delicate outer skeleton made of silica, called the “frustrum,” takes on an unusually diverse range of shapes. These round, triangular, and elongated shells are decorated with patterns of minute holes (halos) that resemble the work of the most skilled goldsmiths.

Until now, scientists have considered that all diatoms account for about one-fifth of Earth's carbon fixation (Matsuda and Kroth, Springer, 2014). But a new study published in the journal Science advances (July 17, 2024) By researchers fromUniversity of California San Diego (UC San Diego) came to disturb this account.

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Diatom consumption of organic matter: 79% of marine samples

Because by dissecting the gene expression (RNA) data collected during the expeditions, Tara OceanThe authors found that not only the split colostium cylindrotheca – A species found in all oceans – it manufactures its own organic matter from dissolved carbon (an “autotrophic” diet), but also consumes it.

Resulting in their proliferation, diatom consumption of organic matter (possibly bacteria) was detected in 79% of the water samples analyzed, often combined with photosynthesis (71%) and sometimes exclusively (8%). There are two types of diet classified respectively as “mixotrophic” and “heterotrophic”.

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“Diatoms are major contributors to marine food webs and key drivers of the global carbon cycle. Previously, we built all carbon cycle models assuming that the only role diatoms played was to fix carbon dioxide. Our results show that this is not the case.“It confirms Professor Karsten Zingler of the University of California, San Diego, who supervised the research (press release).

Reducing the carbon dioxide that these algae remove from the atmosphere

Therefore, the estimates of how much carbon dioxide these algae remove from the atmosphere should be revised downward, according to the study, especially since other widespread species of diatoms could also be affected, something the research team now plans to investigate.

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We believe these results will have major implications for our understanding of the global carbon cycle. Professor Karsten Zingler, University of California, San Diego

On dry lands, too, the carbon cycle seems to hold some troubling surprises. A new study has found that trees store carbon from the atmosphere for less time than expected (Graphene And others.Science, 2024). All of this work will be used to improve the accuracy of climate models.