Seagrass meadows are important sinks for organic carbon and provide co-benefits. However, data on the organic carbon stock in seagrass sediments are scarce for many regions, particularly The Bahamas, which accounts for up to 40.7% of the documented global seagrass area, limiting formulation of blue carbon strategies. Here, we sampled 10 seagrass meadows across an extensive island chain in The Bahamas. We estimate that Bahamas seagrass meadows store 0.42–0.59 Pg organic carbon in the top-meter sediments with an accumulation rate of 2.1–2.9 Tg annually, representing a substantial global blue carbon hotspot. Autochthonous organic carbon in sediments decreased from ~1980 onwards, with concomitant increases in cyanobacterial and mangrove contributions, suggesting disturbance of seagrass ecosystems, likely caused by tourism and maritime traffic activities. This study provides seagrass blue carbon data from a vast, understudied region and contributes to improving climate action for The Bahamas and the Greater Caribbean region.

Conserving blue carbon ecosystems (BCEs) has gained international attention in climate change mitigation, reflected in United Nations policies and voluntary carbon-offset projects. These efforts assume significant and uniform losses of soil organic carbon (C_org) throughout the top meter following disturbances, yet this assumption lacks robust empirical support. Here, we synthesized 239 paired observations of intact and disturbed BCEs globally. Soil C_org stock losses in the top meters vary widely: from −68.4% (agricultural conversion, ±13.4%, 95% confidence interval) to +0.8% (harvesting, ±46.2%) in mangroves, −25.9% (climate/hydrological change, ± 30.7%) to +48.6% (grazing, ±78.7%) in saltmarshes, and −34.2% (vegetation cover damage, ±22.4%) to −27.4% (dredging, ±33.6%) in seagrasses. Extensive disturbances deplete C_org down to 50–200 cm, while limited disturbances impact only the top 10–30 cm or resulted in negligible losses. This refinement contributes to improved global inventories of greenhouse gas emissions from BCEs, supporting abatement policy settings for nationally determined contributions commitments.