Testing the climate intervention potential of ocean afforestation using the Great Atlantic Sargassum Belt

Lennart T. Bach (Lead / Corresponding author), Veronica Tamsitt, Jim Gower, Catriona L. Hurd, John A. Raven, Philip W. Boyd

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    Abstract

    Ensuring that global warming remains <2 °C requires rapid CO 2 emissions reduction. Additionally, 100–900 gigatons CO 2 must be removed from the atmosphere by 2100 using a portfolio of CO 2 removal (CDR) methods. Ocean afforestation, CDR through basin-scale seaweed farming in the open ocean, is seen as a key component of the marine portfolio. Here, we analyse the CDR potential of recent re-occurring trans-basin belts of the floating seaweed Sargassum in the (sub)tropical North Atlantic as a natural analogue for ocean afforestation. We show that two biogeochemical feedbacks, nutrient reallocation and calcification by encrusting marine life, reduce the CDR efficacy of Sargassum by 20–100%. Atmospheric CO 2 influx into the surface seawater, after CO 2-fixation by Sargassum, takes 2.5–18 times longer than the CO 2-deficient seawater remains in contact with the atmosphere, potentially hindering CDR verification. Furthermore, we estimate that increased ocean albedo, due to floating Sargassum, could influence climate radiative forcing more than Sargassum-CDR. Our analysis shows that multifaceted Earth-system feedbacks determine the efficacy of ocean afforestation.

    Original languageEnglish
    Article number2556
    Number of pages10
    JournalNature Communications
    Volume12
    DOIs
    Publication statusPublished - 7 May 2021

    Keywords

    • Carbon cycle
    • Marine biology
    • Ocean sciences

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