Scientists have discovered that violent winter mixing in the North Atlantic can act like an express elevator for carbon, carrying energy-rich organic particles from the ocean surface to depths exceeding 1,000 metres in a matter of days or weeks. The finding reveals that a previously underestimated transport mechanism may move far more carbon into the deep ocean than gravity-driven sinking alone, potentially reshaping how researchers understand the ocean’s role in regulating Earth’s climate.
The study, published in Science Advances and led by the Institute of Marine Sciences of the Spanish National Research Council (ICM-CSIC) and the Barcelona Supercomputing Center–Centro Nacional de Supercomputación, combines observations from autonomous underwater robots with high-resolution computer simulations. Together, the data show that deep winter convection can inject living microalgae and recently produced organic debris into the ocean interior before the material has time to decompose near the surface.
The process begins during the harshest months in regions such as the Labrador and Irminger seas. Cold air and powerful winds strip heat from the ocean surface, causing the water to become denser. When this dense water sinks, it draws surface water downward and generates deep convection, a form of vertical mixing that can reach hundreds or even thousands of metres. These events are part of the large-scale circulation system that connects the world’s oceans and redistributes heat, nutrients and dissolved gases over long timescales.
Carbon enters this system through photosynthesis. Microscopic marine algae, known as phytoplankton, absorb carbon dioxide in sunlit surface waters and convert it into organic matter. Ordinarily, much of this material is consumed by organisms or broken down by microbes as it slowly sinks. Some particles eventually reach the seabed, where their carbon can remain isolated from the atmosphere for decades, centuries or longer. The new research shows that winter convection can bypass much of this gradual “marine snow” pathway by physically transporting fresh particles downward at high speed.
Evidence for the phenomenon came from Biogeochemical-Argo floats, autonomous robots that drift through the ocean while recording temperature, salinity, oxygen, chlorophyll and other chemical and biological properties. Between 2014 and 2017, these instruments detected unexpected peaks of chlorophyll at around 1,000 metres in the Labrador and Irminger seas. Chlorophyll is a key indicator of phytoplankton and is normally concentrated in the sunlit upper ocean, making its presence at such depth a striking signal that surface-derived biological material had been rapidly transported downward.
“Finding these concentrations of chlorophyll—typically found in the sunlit surface layer—at such a depth came as a huge surprise,” said Martí Galí of ICM-CSIC, the study’s lead author. The observations suggested that the particles had descended too quickly to undergo the extensive degradation normally expected during gravitational sinking. Instead, the turbulent downward movement of dense water had carried them into the deep ocean while they were still comparatively fresh and biologically valuable.
To determine how important this mechanism might be beyond the float-observation sites, the researchers used a coupled computer model representing ocean circulation, particle transport and marine biogeochemistry. The simulations were performed on supercomputing infrastructure at the Barcelona Supercomputing Center. By linking the movement of water to the production, transformation and degradation of organic particles, the model allowed the team to estimate how much material was transported, where it traveled and how long its carbon remained in the ocean interior.
The model indicates that the wintertime shortcut can intensify dramatically during severe winters, with transport rates approximately doubling under the strongest mixing conditions. The carbon does not necessarily remain directly beneath the region where it sinks, either. Once injected into the deep ocean, some of the material is carried laterally by currents and redistributed over wide areas. This movement can extend the time carbon remains away from the atmosphere and spread its ecological effects far from the original site of deep convection.
In years with particularly strong winter mixing, the process may account for between 30 and 50 per cent of all organic particles reaching depths between 500 and 2,000 metres. The particles delivered by convection also appear to be rich in energy, providing an unexpected seasonal food supply for deep-ocean ecosystems. Microbes and small animals living far below the surface may therefore receive a sudden pulse of fresh organic matter, even though sunlight cannot penetrate to these depths and local biological production is extremely limited.
The discovery has implications for climate projections because the strength of North Atlantic deep convection is sensitive to changing temperature, freshwater input, winds and sea-ice conditions. Human-driven warming could weaken the density contrasts that make surface water sink, potentially altering the delivery of carbon and food to the deep ocean. The researchers say that sustained observations from satellites, autonomous floats and other robotic platforms will be essential for determining how frequently these underwater cascades occur and how they respond to climate change. Improving their representation in numerical models, including those used by the Intergovernmental Panel on Climate Change, could lead to more accurate predictions of the ocean’s future capacity to store carbon.
Subject of Research: Ocean carbon transport, deep-ocean ecosystems and winter convection in the North Atlantic
Article Title: Convection injects labile particulate organic carbon to the deep ocean
News Publication Date: 31-Jul-2026
Web References: Science Advances article; Institute of Marine Sciences; Barcelona Supercomputing Center
References: Martí Galí et al., “Convection injects labile particulate organic carbon to the deep ocean,” Science Advances 12, eaee6883 (2026). DOI: 10.1126/sciadv.aee6883
Image Credits: Martí Galí Tàpies, Barcelona Supercomputing Center
Keywords: Oceanography, marine carbon cycle, deep convection, North Atlantic, climate change, phytoplankton, biogeochemical-Argo floats, deep ocean, carbon sequestration, marine ecosystems
