Origin and preservation conditions of organic matter in the Mozambique Channel: Evidence for widespread oxidation processes in the deep-water domains

The Mozambique and Madagascar margins present major rivers that are responsible for the discharge of large amounts terrestrial organic matter (OM) which can influence carbon cycling in marine environments. Therefore, channel represents a unique case to study fate deep-water domains. Using new extensive data set sedimentary OM collected from sediment traps, seafloor sediments core sediments, we address origin is transported deposited Channel, its degradation state preservation conditions. A Rock-Eval 6 survey allowed us characterize amount shallow turbidite systems, between 500 4400 m water depth. performed on suspended within particle traps at 47 above seabed show into domain with relatively high TOC (between 1.5 2.5%). However, largely oxidized close water-sediment interface (Oxygen Index >300 mg CO2/g TOC). Seafloor sampled maximum depth 40 cm lower values compared those suggesting mainly active interface. Small concentrations preserved recent distal area Zambezi system below 2500 (TOC < 0.5%). results Majunga slope (NW margin Madagascar) (Mozambique margin) contain highest concentration 1 2%). degraded, probably due conjugate effect low accumulation rates (SARs) permeabilities coarse-grained sediments. Consequently, Channel does not seem be an important sink OM. This process reinforced by bottom currents induce remobilization transport lead higher oxygen exposure time uppermost centimeters