Oceans: particle fragmentation plays a major role in carbon sequestration

A BGC-Argo profiling float equipped with biological and chemical sensors, which can take measurements between the surface of the ocean and a depth of 2,000 metres. D. Luquet, IMEV - A French-British team directed by the Laboratoire d'océanographie de Villefranche-sur-Mer (CNRS/Sorbonne Université) has just discovered that a little known process regulates the capacity of oceans to sequester carbon dioxide (CO₂). It should be noted that photosynthesis performed by phytoplankton on the ocean's surface transforms atmospheric CO₂ into organic particles, some of which later sink to its depths. This essential mechanism sequesters part of oceanic carbon. However, approximately 70% of this particle flux is reduced between a depth of 100 and 1,000 metres. Earlier studies had shown that small animals consume half of it, but no measurements explained what happened to the other half. Using a fleet of robots deployed in different oceans, scientists revealed that approximately 35% of this flux is fragmented into smaller particles.