Carbon burial on river‐dominated continental shelves: Impact of historical changes in sediment loading adjacent to the Mississippi River

Abstract

Seabed cores collected on the continental shelf adjacent to the Mississippi River show a direct temporal correlation between decreases in mass accumulation rate (factor of 2–3) and suspended sediment loads in the river. This mid 20th century decline is not apparent shelf‐wide due to sediment focusing and biological seabed mixing. Total organic carbon diagenetic loss rate across this sediment age interval is relatively uninterrupted when corrected for the non‐steady state mass flux. This suggests that organic carbon burial rates in oxic bottom water settings on river‐dominated continental margins are directly proportional to lithogenic flux. Variations in OM remineralization rates due to changes in the composition (marine vs. terrestrial) of the particulate OM flux at the sediment surface are a second‐order effect that cannot be distinguished in the bulk carbon sediment record at these oxic sites; although they may significantly alter the OM degradation‐induced CO2 flux to the overlying water column.