Organic carbon deposition on the North Carolina continental slope off Cape Hatteras (USA)

The continental slope off Cape Hatteras, NC is a region of high sediment accumulation and organic matter deposition. Sediment accumulation rates range from 3 to 151 cm kyr−1. Organic carbon deposition rates are 5–13 moles C m−2 yr−1, the highest reported for the slope off the eastern US. Burial efficiencies are 3–40%. The organic matter deposited is marine in origin and a mix of old and young particles. High organic carbon deposition rates support remineralization throughout the upper 2–3 m of sediment. Deep bioirrigation to depths of 60–100 cm within the seabed affects the biogeochemistry of the sediments by extending the zone of sulfate reduction and by steepening DIC porewater gradients through the non-local exchange of porewater. Stable and radiocarbon isotope mixing curves for porewater dissolved inorganic carbon (DIC) indicate that the dominant source of DIC accumulating in the upper 2–3 m of the seabed is of nearly uniform δ13C (−21.10‰) and Δ14C (−546‰).