Skip to main content

By Utrecht University

A groundbreaking study by an international team of researchers has revealed seaweed forests to be significant contributors to oceanic carbon storage.

Their research estimates that the world’s seaweed forests transport 56 million tonnes of carbon (between 10 to 170 million tonnes) to deep ocean sinks each year. Between 4 and 44 million tonnes of this carbon could remain sequestered in these deep sinks for at least a hundred years.

This discovery, published in the prestigious journal Nature Geoscience, highlights a considerable contribution of macroalgae to oceanic carbon sinks. The study also suggests that large-scale shifts in seaweed forest distribution and abundance, including past and ongoing losses, would affect the carbon sink capacity. The study thereby provides further impetus for efforts to increase seaweed forests through conservation or restorations.

Seaweed forests, primarily composed of large brown macroalgae like kelps and rockweeds, are among the most extensive and productive vegetated coastal ecosystem on the planet and are hotspots of marine biodiversity. These ocean forests can grow as rapidly as forests on land and are efficient in capturing carbon, which they store in their biomass. Part of this biomass can be transported to deep ocean sinks.

Photo Dr. Karen Filbee Dexter NS
Kelp forests of large brown seaweeds are among the most extensive and productive vegetated natural ecosystems on Earth. These underwater forests are found along >25% of the world’s coastlines, particularly in cooler water where they take up and bind large amounts of carbon in seaweed biomass through photosynthesis. The recent study combined global models of biomass production and export from kelp forests with global oceanographic models to quantify how much seaweed carbon gets exported to deep ocean sinks. The photo shows dense kelp forests (Laminaria hyperborea) – probably the dominant kelp forest on the continent (Photo: Thomas Wernberg, The University of Western Australia)

The study, spearheaded by Dr Karen Filbee-Dexter at the Norwegian Institute of Marine Research and the University of Western Australia, reveals that seaweed forests export about 15% of their captured carbon into deep ocean waters each year, where part of it can remain trapped for centuries. The study estimates that seaweed-carbon export below 200 m depth totaled 3–4% of the ocean carbon sink. The findings thereby underscore the need to include macroalgae in the depictions of the global ocean carbon budget, which still ignores the contribution of marine vegetation.

The international team used state-of-the-art global ocean models to track the fate of seaweed carbon from the coast to the deep ocean. The transport time for macroalgae to the deep ocean was compared to their degradation rate to estimate the fraction that would reach the deep sinks. The team identified hotspots of carbon export globally, for example in areas with extensive seaweed forests or coastal areas with canyons or narrow continental shelves that are close to the deep sea.

“The study identified the seaweed forests of Australia, the USA, New Zealand, Indonesia and Chile as having particularly high carbon removal capacity” said Dr. Filbee-Dexter.

The coastal ocean represents an important global carbon sink and is a focus for interventions to mitigate climate change and meet the Paris Agreement targets while supporting biodiversity.

Utrecht University’s Prof. Jack Middelburg, a co-author of the study, said this research is relevant to conservation, because when seaweed forests are lost, and e.g. replaced by sea urchins, this drawdown of carbon stops. The study underscores the urgent need to act more quickly to protect, manage and restore seaweed forests, which are being lost at alarming rates in many regions of the world due to a variety of human pressures such as ocean warming, marine heatwaves, nutrient pollution, and overfishing.

More information: Karen Filbee-Dexter, Albert Pessarrodona, Morten F. Pedersen et al., ‘Carbon export from seaweed forests to deep ocean sinks’, Nature Geoscience (2024), DOI:10.1038/s41561-024-01449-7. Utrecht UniversityPress Release; Featured image credit: Freepik (AI Gen.)

Asteroid, Earth, Meteorite image
Asteroid impact could trigger global cooling and food chain disruptionScience

Asteroid impact could trigger global cooling and food chain disruption

Summary Scientists simulate asteroid collision effects on climate and plants Summary: A new study published in Science Advances explores the potential consequences of a medium-sized…
SourceSourceFebruary 6, 2025 Full article
Image: Aerial view of a tropical rainforest
Tropical forests struggle to keep pace with climate changeScience

Tropical forests struggle to keep pace with climate change

A major new study has revealed that tropical forests across the Americas are not adapting quickly enough to climate change, raising concerns about their long-term…
SourceSourceApril 4, 2025 Full article
Image: Silhouette of Trees in the Burning Forest
Large wildfires create weather that favors more fireClimateScience

Large wildfires create weather that favors more fire

By Jules Bernstein, University of California - Riverside A new UC Riverside study shows soot from large wildfires in California traps sunlight, making days warmer…
SourceSourceJune 18, 2024 Full article