Seagrass meadows are increasingly recognized for their significant role in burying organic carbon (C) in their sediments. However, this process remains relatively under-studied due to challenges in determining rates of sediment accretion or burial of plant material over IPCC-relevant timescales (>50 – 100 years). Initial estimates suggested that seagrass sediments bury carbon at rates of 138 ± 38 g C m⁻² yr⁻¹ (or 40 - 82 Tg C yr⁻¹ globally). These estimates were based on limited direct assessments of C burial rates, supplemented by measurements of seagrass net community production, which do not necessarily reflect actual C sequestration within the seagrass bed. Over a decade has passed since that initial estimate, and recent local studies suggest seagrass C burial rates should be revised downward, though individual estimates remain dispersed. In this study, we synthesize last century C burial rates in seagrass sediments at regional and global scales to reassess the rate at which seagrass store carbon. We compiled published and unpublished data on sediment accumulation and C burial from 248 seagrass records across 82 global sites, including previously less-studied temperate regions beyond the Mediterranean, as well as additional records (n = 34) from adjacent unvegetated areas. Our results indicate that seagrass ecosystems bury on average 26 ± 4 g C m⁻² yr⁻¹ (geometric mean ± SD), resulting in a global C burial rate between 6.5 and 7.4 Tg C yr⁻¹, based on estimates of the total mapped seagrass area (250,000 – 285,000 km²) reviewed for this study. Although the areal estimate is about one fifth of the previously thought value, seagrass organic carbon burial still accounts for 3% of the total marine carbon burial globally, a disproportionately large contribution considering that seagrass meadows cover less than 0.1% of the ocean surface.
 

seagrass,organic carbon burial,Synthesis,global