1483 / 2024-09-27 17:42:27

Rates of organic carbon accumulation in seagrass sediments globally

seagrass,organic carbon burial,Synthesis,global

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 We compiled published and unpublished data on sediment accumulation and C burial from 248 seagrass records across 82 global sites, including previously less-studied temperate regions beyond the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.