Beyond the rugged cliffs of Southwest Greenland, a hidden “blue carbon” pump is at work, transporting coastal seaweed into the deep abyss to help regulate our planet’s climate.

Knowledge gap

While macroalgae are known for high productivity and carbon assimilation, the specific oceanographic pathways that transport this carbon from rocky shorelines to permanent deep-sea storage have remained largely speculative. Most global carbon export estimates rely on simplifying assumptions because resolving the interplay between biological properties and complex physical ocean transport processes is exceptionally difficult.

Main approach

Our study utilized an interdisciplinary testbed in the Southwest Greenland continental shelf and the Labrador Sea to resolve these pathways. The approach integrated: High-resolution Sentinel-2 satellite imagery to map the distribution of floating algae mats. Tracking data from 305 surface drifters to quantify transport pathways and residence times. Lagrangian particle tracking models (LPTM) to trace the origins and future sinks of detected algal patches. Large Eddy Simulations (LES) to explore the physical mechanisms behind vertical export.

Technological challenge - how we tackle the study

The primary challenge lies in the remote and hostile nature of the Arctic environment. Traditional ship-based observations of deep-sea carbon transport are nearly impossible during intense winter storms when deep convection occurs. To overcome this, we leveraged machine learning-adjacent techniques and numerical simulations to detect nearly 8,000 mats of macroalgae from space and model their behavior in turbulent waters that exceed 2,000 meters in depth.

Main finding

Analysis of over 1,300 satellite images revealed more than 7,900 patches of floating macroalgae, confirming their presence far offshore. Surface currents connect the Greenland shelf to the deep Labrador Sea on timescales of roughly 12 to 63 days, which is short enough for the algae to remain intact and buoyant during transit. Crucially, the simulations demonstrated that wintertime deep convection creates vertical velocities strong enough to draw buoyant algae down to depths where their gas-filled vesicles implode under pressure. This “alternating-turbulence pump” causes the algae to lose buoyancy irreversibly and sink to the deep seafloor for long-term sequestration.

Main implications

These findings underscore the vital role of macroalgal forests in the global biological carbon pump and their potential as significant “blue carbon” contributors. As climate change warms the Arctic, habitat suitability models predict an expansion of these marine forests. Understanding these transport mechanisms is essential for biodiversity management, as it allows us to better account for the carbon storage provided by coastal ecosystems and protects them from human activities like bottom trawling that may disturb these deep-sea sinks.