Organic Carbon Burial in Global Continental Margin Sediments

Continental margin sediments are key long-term sinks for atmospheric carbon dioxide (CO₂). Despite their global significance, the magnitude and spatial distribution of organic carbon (OC) burial in this environment remains poorly quantified mainly due to the exceptional heterogeneity of the coastal ocean. Yet, this knowledge is critical not only for closing the global carbon budget but also for guiding policy decisions. Here, we integrate the rapidly growing observational data set with spatial machine learning and inverse as well as forward reaction-transport modelling, capturing the spatial heterogeneity of global continental margins to deliver robust OC flux estimates.

We estimate a global continental margin OC burial flux of 441 Tg C yr⁻¹ through the base of the mixed layer, decreasing to 293 Tg C yr⁻¹ at the 1 kyr age horizon (<1–33 m sediment depth). Approximately 70% of this burial occurs in the northern hemisphere, and >50% is concentrated within the latitudinal band 10°S–30°N. Using the MARgins and CATchments Segmentation framework, tropical regions show the highest OC flux densities and total long-term burial flux globally (5.4 tC km^-2 yr⁻¹ and 64 Tg C yr⁻¹). In addition, polar regions and marginal seas also reveal high total long-term burial fluxes (42 Tg C yr⁻¹ and 35 Tg C yr⁻¹). In polar regions, high burial is driven by modest OC flux densities over vast areas, while marginal seas exhibit high flux densities but limited spatial extent. Each of the other MARCAT regions contributes less than 15% to global OC burial. We thus find the highest OC burial rates in the Exclusive Economic Zones (EEZs) of Indonesia (27 Tg C yr⁻¹) and Russia (20 Tg C yr⁻¹), followed by the EEZs of the Philipines, Antarctica, the United States, Japan, Papua New Guinea, Canada, New Zealand, Brazil, Yemen, and Mexico (each accounting for 2-5% of global OC burial). The EU EEZs collectively bury approximately as much OC as the Russian EEZ.

When combined with global radiocarbon data for organic carbon (OC), our global estimates reveal several hotspots of young, marine-derived OC burial that actively remove contemporary atmospheric CO₂. These regions include tropical margins such as the Sunda Shelf, the Caribbean coastal zones, the western coast of Mexico, and the South China Sea, as well as marginal seas. In contrast, other burial hotspots—such as tropical margins adjacent to large river deltas or the Arctic shelf—predominantly sequester older, pre-aged terrestrial OC and petrogenic OC. While OC burial in these areas has a limited direct impact on contemporary CO₂ levels, it plays a crucial role in the modern carbon cycle by preventing the release of this geological carbon through microbial degradation.