On the Atlantic pelagic Sargassum's role in carbon fixation and sequestration

Abstract The extensive blooms of the pelagic Sargassum in the Atlantic raised the question of whether this brown seaweed may play an important role in climate change mitigation through carbon fixation and carbon sequestration, as argued in several recent papers. Using simple calculations and published values on Sargassum coverage, biomass density, carbon/biomass ratio, primary productivity, and carbon sequestration efficiency, we show that the total carbon stock in pelagic Sargassum of the entire Atlantic, even during the peak month, is unlikely to exceed 3.61 × 10−3 Pg C, and carbon fixation cannot exceed 6.0 million tons C month−1. While the carbon fixation estimate represents an upper bound, it is still