Substantial role of macroalgae in marine carbon sequestration

Abstract

Vegetated coastal habitats have been identified as important carbon sinks. In contrast to angiosperm-based habitats such as seagrass meadows, salt marshes and mangroves, marine macroalgae have largely been excluded from discussions of marine carbon sinks. Macroalgae are the dominant primary producers in the coastal zone, but they typically do not grow in habitats that are considered to accumulate large stocks of organic carbon. However, the presence of macroalgal carbon in the deep sea and sediments, where it is effectively sequestered from the atmosphere, has been reported. A synthesis of these data suggests that macroalgae could represent an important source of the carbon sequestered in marine sediments and the deep ocean. We propose two main modes for the transport of macroalgae to the deep ocean and sediments: macroalgal material drifting through submarine canyons, and the sinking of negatively buoyant macroalgal detritus. A rough estimate suggests that macroalgae could sequester about 173 TgC yr−1 (with a range of 61–268 TgC yr−1) globally. About 90% of this sequestration occurs through export to the deep sea, and the rest through burial in coastal sediments. This estimate exceeds that for carbon sequestered in angiosperm-based coastal habitats.

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Figure 1: Map of the locations where macroalgal carbon storage has been reported.
Figure 2: Conceptual diagram of the pathways for export and sequestration of macroalgal carbon.

KING ABDULLAH UNIVERSITY OF SCIENCE AND TECHNOLOGY

Figure 3: Pathways for the sequestration of macroalgal carbon in the ocean.

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Acknowledgements

The study was funded by the COCOA project under the BONUS programme, which is funded by the EU 7th Framework Programme, the Danish Research Council and KAUST. We thank I. Gromicho (KAUST) for the artwork in Fig. 2 and A. Kjeldgaard and T. Christensen for help with Fig. 1. The study is also a contribution to the Greenland Ecosystem Monitoring programme (www.G-E-M.dk) and the Arctic Science Partnership (www.asp-net.org).

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Correspondence to Dorte Krause-Jensen.

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Krause-Jensen, D., Duarte, C. Substantial role of macroalgae in marine carbon sequestration. Nature Geosci 9, 737–742 (2016). https://doi.org/10.1038/ngeo2790

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