Sequestration of terrigenous organic carbon on the northern California shelf: The role of hyperpycnal flows

Mountainous rivers that drain active continental margins deliver a significant fraction of particulate organic carbon (POC) to the oceans, which makes such river systems a key component of the global carbon cycle. Understanding the fate of terrigenous organic carbon in the ocean is important for quantifying ocean carbon budgets over long periods of time. This research gives insight on the fate of POC in active continental margins, such as the Eel River margin. The Eel River margin has such a narrow shelf (10--20 kilometers) and high suspended sediment concentration (>40g/L) during flood events that a large fraction of terrigenous sediment is dispersed by hyperpycnal flows (river density greater than ocean density) and bypasses the shelf. Three piston cores were acquired on the Humboldt Slide and one piston core was taken away from the site, serving as a control. The geochemical signature of the POC layers present in the cores was determined using an Avaatech x-ray fluorescence (XRF) core scanner. The downcore elemental profiles were also used to study the sedimentation history on the Humboldt Slide. Mechanisms identified as controlling sedimentary processes on the Eel River margin and resulting in the sequestration of terrigenous organic carbon in the ocean are earthquake and precipitation-induced landslides as well as storm-driven fluvial discharge.