Organic Matter Sequestration in Oregon Margin Sediments: Tectonic, Climatic and Oceanographic Controls

Abstract:

A combination of box, gravity and piston cores from a site on the upper slope off the Umpqua River in the central Oregon margin were used to create a high-resolution record of organic matter burial over the past ~13,000 years. Our objective is to understand how variations in precipitation intensity and frequency, tectonic uplift rates, and topographic relief affect the magnitude and composition of organic matter deposited along this margin. To examine the possible tectonic and climatic factors influencing the land-ocean relationship of Cascadia during the late Holocene, we measured the organic carbon content, carbon-nitrogen ratio, stable isotopic compositions of organic carbon, yields of lignin-derived and lipid-derived constituents, and mineral surface area of collected sediments from box, kasten and piston cores. Decreases in several organic constituents revealed a potential preferential degradation of marine organic matter over time. Lignin phenol abundances oscillated downcore, pointing towards changes in the provenance of terrigenous organic matter transported to this site. Primary component analysis (PCA) illustrated distinct marine and terrestrial organic matter-dominated segments of the record, which will be correlated to eustatic, tectonic and climatic forcings over the late Holocene.