Mechanical shortcut' rapidly carries organic particles into the deep ocean

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Add as preferred source The processes that capture carbon from the atmosphere and store it on the seabed are crucial for climate balance. However, assessing these mechanisms is often complicated because it requires measurements ranging from the surface to the deep ocean.

Now, a new study published in the journal Science Advances and led by the Institute of Marine Sciences (ICM-CSIC) and the Barcelona Supercomputing Center – Centro Nacional de Supercomputación (BSC-CNS) has made it possible to observe and quantify a key transport pathway: Large-scale winter upwelling of surface water rapidly delivers nutrient-rich organic particles to depths of more than 1,000 meters (3,280 feet).

In regions such as the subpolar North Atlantic , cold, strong winter winds cool surface water, making it denser and heavier and causing it to sink rapidly. This process, known as "deep convection," fuels currents that connect all the oceans over centuries and helps regulate the global climate and carbon storage in the ocean.

The study demonstrates that this "underwater cascade" acts as a mechanical shortcut, carrying living microalgae and organic debris to the seabed much more rapidly and to greater depths than previously thought. This transport is intermittent and regional in scope but far more efficient than the sedimentation of particles by gravity, the dominant transport mechanism.

To carry out the study, the scientific team combined real-world data with sophisticated computer simulations. On the one hand, they analyzed data from a fleet of autonomous underwater robots, known as Biogeochemical-Argo floats , that drift and take measurements at depths of around 1,000 meters (3,280 feet). Thanks to these devices, surprising peaks of chlorophyll have been detected in the depths of the Labrador and Irminger seas, coinciding with intense episodes of surface-water sinking that occurred between 2014 and 2017.

"Finding these concentrations of chlorophyll—typically found in the sunlit surface layer—at such a depth came as a huge surprise, because normally it would have broken down long before reaching that depth," explains Martí Galí, a researcher at ICM-CSIC and lead author of the study. "These data allow us to quantify a previously little-known source of carbon within the ocean and open up a vast range of possibilities for using these robots as the eyes of science in the deep ocean."

To calculate the scale of this shortcut globally, the researchers used a computer model that simulates marine physics and biogeochemistry. The simulations were run using the BSC's supercomputing resources.

"The story began right here at BSC, where we realized that we needed to better link these large-scale water movements with the carbon cycles," recalls Raffaele Bernardello, a researcher in the BSC's Earth Sciences Department and co-author of the study. "The simulations have enabled us to estimate that transport doubles during the harshest winters and that the carbon does not remain stagnant; rather, some of it travels laterally and is stored far from the area where it has sunk, prolonging its positive effect on the climate."

Furthermore, the study indicates that in years of strong winter mixing, this mechanism contributes between 30% and 50% of all organic particles reaching layers between 500 and 2,000 meters (1,640 to 6,560 feet). By analyzing the properties of particles at 1,000 meters (3,280 feet) and comparing them with those observed by satellites at the surface, researchers found that the injected material is very rich and full of energy.

Maria Andrea Orihuela-García, who is completing her doctoral thesis at ICM-CSIC in association with BSC, highlights the implications for deep-sea ecosystems: "This process not only serves to capture carbon from the atmosphere but also sends energy directly downward. These vertical currents act as an unexpected seasonal feast that nourishes and energizes communities of microbes and small animals living in the deep ocean."

Against this backdrop, the team emphasizes the need for further research in this area to improve observations of this phenomenon and its representation in numerical models, including those of the Intergovernmental Panel on Climate Change (IPCC). The team also emphasizes the need to maintain and strengthen ocean observation systems using satellites and autonomous robots, particularly the Argo program, an international collaborative effort based on the principles of open science.

Finally, at a time when human activity is altering the planet's climate and threatening to weaken water downwelling in the North Atlantic, a highly significant process, constant global monitoring of the ocean—from the surface to the depths—is becoming more important than ever for understanding and predicting climate change.

Martí Galí et al, Convection injects labile particulate organic carbon to the deep ocean, Science Advances (2026). DOI: 10.1126/sciadv.aee6883

Provided by Barcelona Supercomputing Center

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