Influence of oxygen exposure time on organic carbon preservation in continental margin sediments

Abstract

Today, over 90% of all organic carbon burial in the ocean occurs in continental margin sediments1. This burial is intrinsically linked to the cycling of biogeochemically important elements (such as N, P, S, Fe and Mn) and, on geological timescales, largely controls the oxygen content of the atmosphere2,3,4. Currently there is a volatile debate over which processes govern sedimentary organic carbon preservation5,6,7,8. In spite of numerous studies demonstrating empirical relationships between organic carbon burial and such factors as primary productivity9, the flux of organic carbon through the water column10, sedimentation rate11,12, organic carbon degradation rate13, and bottom-water oxygen concentration8,14, the mechanisms directly controlling sedimentary organic carbon preservation remain unclear. Furthermore, as organic carbon burial is the process that, along with pyrite burial15, balances O2 concentrations in the atmosphere, it is desirable that any mechanism proposed to control organic carbon preservation include a feedback buffering atmospheric oxygen concentrations over geological time. Here we compare analyses of sediments underlying two regions of the eastern North Pacific Ocean, one which has oxygen-depleted bottom waters and one with typical oxygen distributions. Organic carbon burial efficiency is strongly correlated with the length of time accumulating particles are exposed to molecular oxygen in sediment pore waters. Oxygen exposure time effectively incorporates other proposed environmental variables8,9,10,11,12,13,14, and may exert a direct control on sedimentary organic carbon preservation and atmospheric oxygen concentrations.