Shallow coastal zones play a larger role than expected in Arctic carbon transport

A new study indicates that the nearshore zone along Arctic coastlines could play a more vital role in carbon cycling than scientists previously assumed.

The research team from the Vrije Universiteit Amsterdam, led by Fleur van Crimpen and including Joost van Genuchten from the iC3 Polar Research Hub, found that the shallow nearshore zone traps large amounts of organic carbon released from thawing permafrost. 

This means that a larger proportion of the carbon, previously thought to be transported into the Arctic shelf, instead stays close to shore and may be broken down to CO2 or stored there. This result challenges current assumptions about Arctic land-ocean carbon transport and could have important implications for climate feedbacks.

Credit: van Crimpen (2025),  Nature Commun Earth Environ 6, 909.

Shallow coastal waters shape the fate of permafrost carbon

Permafrost coasts around the Arctic are eroding rapidly as the region warms. This releases vast amounts of terrestrial organic carbon, mostly old plant material – including vascular plant material, which is high in organic carbon – into coastal waters. 

Exactly what happens to this carbon in shallow coastal zones has not been studied much due to logistical constraints. This new study focuses on the shallow waters (less than 5 metres deep) off the Canadian Beaufort Sea. where eroded material first arrives.

Using samples of sediments and surface waters along the coast, the team found that nearly half of terrestrial organic carbon arriving in the ocean is in a low-density form, mainly loose plant debris. Rather than floating offshore, as much as half of this material becomes waterlogged and heavy, causing it to settle in shallow waters instead of being transported to deeper parts of the shelf. Less than one tenth of this material reaches depths of 30–55 metres.

Credit: Fleur van Crimpen (NIOO-KNAW).

Lead author Fleur van Crimpen from the Vrije Universiteit Amsterdam explains: 

“We were surprised at how much of the permafrost-derived carbon gets trapped close to shore. These shallow zones aren’t just passive conduits; they act like sinks where carbon can be broken down or buried before it ever reaches the deep ocean.”

Co-author Joost van Genuchten from the iC3 Polar Research Hub adds: 

“These shallow coastal zones seem to play an essential role in the cycling of carbon in this area. Recognising their role could possibly sharpen our understanding of land-ocean carbon fluxes and the fate of coastal permafrost.”

Shallow coastal areas remain understudied

Despite their apparent importance, shallow coastal waters are rarely included in Arctic shelf studies. Shallow coastal waters make up only a tiny fraction of Arctic shelf sampling to date; less than six per cent of available sediment data comes from depths shallower than five metres.

The study’s authors argue that expanding observations in these zones is essential for understanding the coastal carbon dynamics.

Find out more

The study “Shallow coastal zones are key mediators in Arctic land-ocean carbon fluxes” is available open access in Nature Communications Earth & Environment.

Lead author Fleur van Crimpen now works as a postdoctoral researcher at the Department of Aquatic Ecology at the Netherlands Institute of Ecology on drivers of methane in Greenland.

Joost van Genuchten is a PhD researcher at the iC3 Polar Research Hub within the Department of Geosciences at UiT The Arctic University of Norway. He contributed to this study during an internship at Vrije Universiteit Amsterdam. His current research focuses on the methane dynamics in proglacial lakes in Greenland. To find out more about his work, please read this story.