Un raccourci mécanique transporte rapidement des particules organiques dans les profondeurs de l'océan.

A newly discovered oceanic process called the "mechanical shortcut" has been identified as a major contributor to the rapid transport of organic particles from the surface to the deep ocean, according to a study published in Science Advances. Led by the Institute of Marine Sciences (ICM-CSIC) and the Barcelona Supercomputing Center (BSC-CNS), the research reveals how seasonal changes drive the movement of nutrient-rich organic matter to depths exceeding 1,000 meters (3,280 feet), significantly altering our understanding of oceanic carbon cycling. The phenomenon occurs primarily in the subpolar North Atlantic, where cold, strong winter winds cause surface waters to cool and become denser. As a result, these dense, cooled waters sink rapidly, a process known as "deep convection." This leads to the formation of powerful ocean currents that span the globe and play a critical role in regulating climate and storing carbon in the ocean. The study shows that this deep convection triggers a "mechanical shortcut," enabling the swift delivery of living microalgae and organic debris to the seabed, bypassing the slower, gravity-driven sedimentation typically responsible for particle transport. The discovery was made through a combination of field observations and advanced computational modeling. Researchers deployed a network of autonomous underwater robots known as Biogeochemical-Argo floats, which drift and collect data at depths of approximately 1,000 meters. These instruments recorded unexpected spikes in chlorophyll levels in the Labrador and Irminger Seas, aligning with periods of intense surface-water sinking between 2014 and 2017. Such findings were surprising, as chlorophyll is usually confined to the sunlit surface layer and should degrade before reaching such depths. Martí Galí, a researcher at ICM-CSIC and lead author of the study, noted that these observations allowed scientists to quantify a previously underappreciated source of carbon within the ocean. He emphasized that the data collected by the floats provide valuable insights into the dynamics of deep-sea carbon transfer and highlight the potential of robotic systems as tools for exploring the ocean’s hidden realms. To understand the broader implications of this process, the research team utilized high-performance computing resources at the BSC. A simulation model was developed to integrate marine physical and biogeochemical processes, offering a comprehensive view of how carbon moves through the ocean system. According to Raffaele Bernardello, a researcher at BSC and co-author of the study, the simulations revealed that during particularly harsh winters, the rate of carbon transport can double. Moreover, the study suggests that some of the transported carbon does not remain localized but instead spreads laterally, contributing to carbon storage in distant areas and extending its climatic impact. Further analysis of particle composition showed that the organic material delivered to depths of 1,000 meters is highly energetic and rich in nutrients. Maria Andrea Orihuela-García, a doctoral candidate at ICM-CSIC working with BSC, highlighted the ecological significance of this process. She explained that the transport not only captures atmospheric carbon but also provides essential energy to deep-sea ecosystems, supporting life in otherwise resource-limited environments. As the research continues, scientists aim to refine their models and expand the geographic scope of their studies to better predict how these mechanical shortcuts influence global carbon cycles and climate regulation. With ongoing advancements in oceanographic technology and computational power, the future holds promise for deeper exploration of the ocean’s complex and dynamic systems.