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The Role of Seaweed in Oceanic Carbon Sequestration

An international group of researchers revealed that seaweed forests play a significant role in capturing and storing carbon dioxide in the deep ocean. Researchers estimated that seaweed forests transport millions of tons of carbon each year, contributing to the fight against climate change. The findings highlight the importance of protecting and restoring these vital underwater ecosystems. The research was published in the journal Nature Geoscience.

The Role of Seaweed in Oceanic Carbon Sequestration

Image Credit: Ethan Daniels/

According to the findings, global seaweed forests transfer between 10 and 170 million tonnes of carbon to deep ocean sinks annually, with 56 million tonnes being the average. Of this, between 4 and 44 million tonnes could be sequestered in these deep sinks for a minimum of one hundred years.

This study emphasizes the significant role that macroalgae play as oceanic carbon sinks. It also implies that significant changes in the number and distribution of seaweed forests, including past and present losses, would impact the carbon sink capacity. Thus, the study offers more motivation for initiatives aimed at expanding seaweed forests via preservation or restoration.

Seaweed forests are hotspots for marine biodiversity and are among the world's most expansive and productive vegetated coastal ecosystems. They are mainly made up of huge brown macroalgae like kelps and rockweeds.

These ocean forests are effective at absorbing carbon, which they store in their biomass. They can develop just as quickly as forests on land, and some of this biomass can be moved to sinks in the deep ocean.

The research, led by Dr. Karen Filbee-Dexter of the University of Western Australia and the Norwegian Institute of Marine Research, shows that each year, seaweed forests transfer roughly 15 % of the carbon they have sequestered into deep ocean waters, where some of it can stay trapped for millennia.

According to the study, 3-4 % of the ocean's carbon sink is attributed to seaweed carbon exported below 200 m of depth. The results thus highlight the necessity of incorporating macroalgae into models of the global ocean carbon budget, as they currently do not account for the contribution of marine vegetation.

The international team employed cutting-edge global ocean models to trace the path of carbon from seaweed from coastal areas to the deep ocean. They compared the time it takes for macroalgae to reach the deep ocean against their rate of degradation to estimate how much carbon would make it to deep sinks.

Additionally, the team pinpointed global hotspots for carbon export, such as regions with large seaweed forests or coastal zones near deep sea areas, which feature canyons or narrow continental shelves.

The study identified the seaweed forests of Australia, the USA, New Zealand, Indonesia, and Chile as having particularly high carbon removal capacity.

Dr. Karen Filbee-Dexter, School of Biological Sciences and Oceans Institute, University of Western Australia

The coastal ocean serves as a major global carbon sink and is the target of interventions aimed at reducing global warming, meeting the targets set forth in the Paris Agreement, and preserving biodiversity.

Co-author of the research, Professor Jack Middelburg of Utrecht University, emphasized the importance of this research for conservation. He explained that the loss of seaweed forests, often replaced by sea urchins, halts the drawdown of carbon.

The study highlights the critical need for accelerated efforts to protect, manage, and restore seaweed forests. These vital ecosystems are disappearing rapidly in many regions worldwide due to various human-induced pressures, including ocean warming, marine heatwaves, nutrient pollution, and overfishing.

Journal Reference:

 Filbee-Dexter, K., et al. (2024) Carbon export from seaweed forests to deep ocean sinks. Nature Geoscience.

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