Continental shelves are integral to the global carbon cycle, yet uncertainties persist about the nature and extent of carbon burial, particularly in sand-dominated areas. In the sand-dominated North Sea, the Helgoland Mud Area (HMA) emerges as a small-size mud depocenter, surrounded by sandy sediments that do not accumulate organic carbon (OC) and are separated from adjacent rivers. Such small-size depocenters, common on high-energy shelves, have underexplored OC degradation and burial efficiencies due to their limited individual size. Since sandy sediments with interspersed small-size depocenter cover ∼50 % of global shelves, these depocenters may collectively offer greater OC burial capacity than previously recognized. This study investigated the composition, degradation, and sequestration of OC from terrestrial (OCterr) and marine (OCmar) sources in surface sediments of the HMA and adjacent sandy areas using bulk (mean grain size, OC content, loading and 13C isotope composition) and molecular (fatty acids and alkanes) analyses. Our results, derived from a two end-member mixing model based on δ13C values of bulk OC, revealed that OCterr dominates (∼74 %) the sedimentary OC in both areas, with OCmar contributing ∼26 %. The HMA exhibited OCterr and OCmar contents ∼5 times higher than in the sandy areas. Both OCterr and OCmar loadings negatively correlated with mean grain size, indicating reduced OC degradation in muddy sediments. Molecular analysis further revealed that OCterr in the HMA is less refractory compared to adjacent sandy regions. These differences are attributed to differences in porewater transport, oxygen penetration depths and exposure times, all of which influence OC preservation, despite the important role of mineral protection. OCterr and OCmar accumulation fluxes in the HMA were calculated at (6.75 ± 0.61) × 10−3 and (2.54 ± 0.68) × 10−3 Tg C/yr, respectively, representing 34.3 % of OCterr export from adjacent rivers and 2.8 % of net OCmar production in the HMA. These values are twice the global average for shelf areas, highlighting the exceptional efficiency of the HMA as a carbon sink and hinting at the significance of small-size depocenters within sandy areas in the global carbon cycle.