Scientific publication

The key role of seaweed forests in global carbon sequestration

Credits: Photo by Richard Shucksmith

The coastal ocean plays a crucial role as a global carbon sink, essential for climate change mitigation efforts and the achievement of the Paris Agreement targets. This critical function also supports biodiversity and other ecosystem services. However, a significant gap in our understanding of marine carbon budgets is the fate of carbon exported from seaweed forests, the largest vegetated ecosystems along our coasts.

Our research has provided groundbreaking national and global estimates of particulate carbon export from seaweed forests to depths below 200 meters, revealing that this process accounts for 3-4% of the ocean’s carbon sink capacity. The study utilized sophisticated models to assess seaweed forest extent, production, decomposition, and the exchange of water between the continental shelf and the open ocean.

Key findings:

  1. Seaweed Carbon Export: On average, 15% of seaweed production is exported beyond the continental shelf. This translates to an estimated 56 teragrams of carbon per year (TgC yr−1), with a range between 10 and 170 TgC yr−1.

  2. Sequestration Potential: Of the exported carbon, it is estimated that 4 to 44 Tg of seaweed-derived carbon could be sequestered for up to 100 years at depths below 200 meters annually.

These insights underscore the significant but previously underappreciated role of seaweed forests in carbon sequestration. Although the study did not account for shelf burial and dissolved and refractory carbon pathways, it highlights the substantial potential of seaweed as a natural carbon sink.

Implications for conservation and climate mitigation

Understanding the full extent of seaweed carbon sequestration is crucial for guiding conservation efforts, particularly as seaweed forests face global declines. Protecting and restoring these ecosystems could enhance their carbon sequestration potential, contributing to climate mitigation strategies.

This research underscores the importance of seaweed forests in the global carbon cycle. By continuing to investigate and understand the mechanisms behind seaweed carbon export and sequestration, we can better inform conservation policies and climate change mitigation efforts. Protecting these vital ecosystems is not only essential for biodiversity but also for sustaining their role as natural carbon sinks in our fight against climate change.

Main reference

Filbee-Dexter, K., Pessarrodona, A., Pedersen, M.F. et al. Carbon export from seaweed forests to deep ocean sinks. Nat. Geosci. (2024).

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Jorge Assis [PhD, Associate Researcher]
Centre of Marine Sciences, University of Algarve [Faro, Portugal]
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