Seaweed’s unsung carbon capturing potential

The study doubles previous estimates of coastal macroalgae’s capacity to capture and store atmospheric CO₂, a long-term process called carbon sequestration. 

Generally, macroalgae contribute to oceanic photosynthesis, and until this study, scientists thought that its photosynthetic production was released back into the atmosphere as CO₂. Most macroalgae grow on rocky shores, where detritus cannot be buried in sediments, so they thought it was releases into the water, where it would be decomposed by bacteria and released back as CO₂.

But these researchers are now contesting this. “Our analysis shows that a large fraction of their photosynthetic production is sequestered into marine soils or the deep sea or both,” says Carlos M. Duarte, a marine scientist at King Abdullah University of Science and Technology, and co-author of this study. 

According to Duarte, macroalgae can globally sequester CO₂ roughly equivalent to emissions of 35 million Saudi citizens.

Macroalgae often attach to floating structures that keep them adrift on the surface. Duarte and his team thereby suggest two modes by which macroalgae are transported to the deep ocean and sediments, where their CO₂ content is sequestered; dislodgment during storms and “ballasting” of the macroalage. The latter happens when the algae attach themselves to stones and boulders that eventually sink into the deep sea.  

“Management actions can help maintain such carbon sinks by conserving kelps and macroalgal forests,” says Duarte.

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