Carbon sequestration potential increased by incomplete anaerobic decomposition of kelp detritus

Kelps are highly productive macroalgae that form habitats along one-quarter of the worlds’ coastlines. Emerging evidence suggests kelps have potential to sequester carbon through export detritus deep marine sinks, yet how much this detrital is remineralized grazing and microbial decomposition before it reaches these sinks remains a critical knowledge gap. We measured decay Laminaria hyperborea in shallow kelp forests (10 m) adjacent fjords (300 m), experimentally tested effect temperature oxygen conditions similar those at ex situ experiments. Initial rate ( k ) was high (-0.107 -0.183 d -1 with 40-60% original biomass being lost within few weeks, after which rates slowed down = -0.009 -0.038 ). Temperature had little on extent range (4-10°C). Blade decomposed almost completely 300 under aerobic conditions. Anaerobic both blade stipe ceased, contrast, 150-200 d, leaving 20-30% initial decompose extremely slowly or not all. Decomposition followed by changes chemical composition; C:N ratios increased substantially, while mannitol phenolics disappeared from matrix. Slow incomplete anaerobic suggest for long-term burial sequestration will be enhanced if exported nearby areas permanent periodic hypoxia near bottom.