Temporal and spatial changes in organic carbon sequestration in shelf sediments along a fluvially influenced margin

Oregon State University, Corvallis OR

Investigators

Abstract

Rivers transport large amounts of sediment and organic carbon (OC) from land to the ocean, with much of this material deposited on the continental shelf. These shallow environments are therefore important for OC burial and storage. However, knowing the amount and long-term stability of this OC is challenging because of changing conditions in coastal systems. This project will revisit a shelf region off the Umpqua River in central Oregon that was sampled in 2009 to see whether sedimentation and OC deposition have changed over time. The researchers will conduct detailed geophysical mapping and collect new sediment cores for physical and geochemical analyses. By combining these new data with the previous measurements, the researchers can quantify spatial and temporal changes in deposition. They will try to link any observed changes to factors like river sediment load, wave-energy, seasonal low-oxygen zones, and groundfish trawling. A group of undergraduate students will participate in the research as part of a two-year Undergraduate Research Experience. Students will sail on the research cruise, gaining hands-on experience in field oceanography, and will then work in teams to analyze samples, process and visualize data, and communicate results. The Umpqua River depocenter offers a unique opportunity to gain understanding of OC burial flux and stability in shelf environments because it is small enough to be feasibly mapped and sampled in a single expedition, has experienced marked, documented environmental changes, and is representative of marine sediment dispersal/depositional systems globally. This project will combine geophysical mapping with comprehensive re-sampling of locations previously cored in 2009. Sediment multi-cores will be imaged via X-radiography or CT scanning, analyzed for physical properties including bulk density and grain size, and dated using Pb-210 and Cs-137 isotopes. Sediment will be analyzed for OC and nitrogen content and OC composition. If sediment and OC deposition and storage have changed over the intervening years, researchers can use the combined datasets to identify the primary drivers of change and predict the response of OC sequestration to future environmental variability. Conversely, if OC storage has not changed, then it will be possible to compile carbon storage data from multiple decades of studies in U.S. margin environments to generate estimates of total carbon storage. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.