In ocean surface waters, diatoms convert dissolved atmospheric CO₂ into "organic" carbon, which, after their death, falls to the depths. Nonetheless, this carbon is rapidly degraded in the form of carbon dioxide before reaching a depth of 1,000 meters.

This view has been corrected by recent observations and simulations that demonstrate the predominance of diatoms, not only in surface waters but also in other ocean compartments. Moreover, the size of diatoms (ranging from 2 microns to one millimeter), their morphology, their silicon and carbon composition and their environment are all factors that strongly influence their effectiveness as "carbon pumps".

The researchers thus demonstrated that diatoms can occasionally transport large quantities of organic carbon to the deepest layers of the ocean, where it remains stored for more than a century. This means that carbon transfer in the ocean depths attributable to diatoms has been underestimated until now.

However, several simulations predict a global decline in diatoms (except in the Antarctic Ocean) and consequently a decrease in their carbon transfer to the ocean depths, although the adaptations of these species to climate change and acidification could contradict these projections. The evolution of the ocean carbon pump is therefore complex and cannot be described by simplified ocean models.

This work, conducted by an international team led by researchers from the European University Institute of the Sea (Université de Bretagne occidentale, CNRS, IRD), demonstrates the need for multidisciplinary strategies in order to understand these essential mechanisms of global climate change.