Organic Carbon Burial in Global Continental Margin Sediments

Abstract Continental margins, situated at the nexus of land and ocean, act as major burial hotspots for terrestrial and marine organic matter, creating a critical interface between the short-term carbon cycle and long-term geological storage. Although this burial largely regulates atmospheric CO₂, O₂ and thus climate, its magnitude and spatial distribution remain poorly constrained due to sparse observations and an extraordinary environmental variability. Here we present the first global, observation-constrained assessment of organic-carbon transfer and burial along the global continental margin, integrating observational data with spatial machine learning and three-dimensional reaction–transport modelling. We estimate a global organic-carbon transfer flux of 367 Tg C yr⁻¹ on centennial timescales, decreasing to 293 and 246 Tg C yr⁻¹ on millennial and multi-millennial scales. These results show that continental-margin sediments form one of Earth’s largest and most persistent long-term carbon sinks, exceeding lakes, reservoirs and all major vegetated coastal ecosystems combined. Burial is strongly heterogeneous, with ~70% occurring in the Northern Hemisphere and ~50% in equatorial regions, and with pronounced hotspots in tropical margins and marginal seas. These findings reduce a central uncertainty in the coastal carbon budget and thus refine global carbon cycle assessments, constrain ocean–atmosphere CO₂ exchange, and provide the first spatial framework to guide marine conservation, management, and climate policy.