Organic Matter Distribution is Controlled by Sedimentological Parameters in Marine Oxygen Minimum Zone

Summary Organic matter (OM) in marine sediment is usually associated with mineral surfaces because it offers protection from degradation. As the amount of OM on a particle increases, so does its grain size, but its density decreases. The reduced density of the surface sediment results in a high propensity for resuspension, therefore aggregate transport represents an efficient way to relocate OM to offshore sites and depocentres on the continental slope. This process has significant effects on reconstructing past environments as OM is laterally displaced from where it was produced. OM abundance in sediments is negatively correlated to oxygenation state; hence, oxygen minimum zones are often characterised by a soft, soupy sediment surface. We study samples from the Benguela upwelling system offshore Namibia, where widespread lateral transport has been described and significant age differences are reported between compounds (alkenones, crenarchaeol), calcareous shells, and bulk organic carbon. Working with the comprehensive dataset on environmental tracers on the Benguela upwelling system, we use bulk molecular tracers on core-top samples and their respective grain size and density fractions to trace resuspension effects on sedimentary OC ageing in anoxic and oxic water condition.