PhD Dissertation Defense: Emily Elliott

The Ph.D. Dissertation Defense of Emily Elliott will be presented at Murray Hall, in the 3rd floor conference room #3204 of the Marine Sciences Department, UNC at Chapel Hill and live broadcast to UNC Institute of Marine Science (IMS) in Morehead City, NC. This event will be held on Thursday, March 23rd, 2017 at 11:00 AM.

Title: Raiding the toolbox – Techniques for Assessing Historical High-Resolution Records of Coastal and Estuarine Sediment Erosion, Transport and Sedimentation

Abstract: Estuaries act as a buffers to material transport from terrestrial to oceanic environments. Characterizing mechanisms of erosion, transport and sedimentation within estuaries is crucial for understanding material flux to the marine environment and compositional transformations. However, obtaining multi-decadal high-resolution records of sediment flux, source, and composition within estuaries is a major challenge in coastal research due to dynamic processes that actively erode, resuspend and/or rework the sedimentary record. For this reason, estuarine sedimentology has dominantly focused on either long-term (decadal to millennial) records that show constant sedimentation rates often matching the rate of sea-level rise, or short-term (multi-year to decadal) studies that show variable sedimentation rates associated with events.

This dissertation presents a monthly record of estuarine sedimentation that spans ~40 years within a highly accreting mini-basin, Cape Lookout Bight (CLB), NC, utilizing existing and newly-developed methods. This long-term high-resolution record is used to identify the dominant physical drivers of sediment flux within and through the estuary.

In this presentation, the lithologic and the long-term geochronology of this basin is used to determine its formation and sediment sources through time. Using a developed and tested modified time-integrated mass suspended sediment sampler (TIMS) design, developed through this work for the collection of suspended sediment within tidal flow environments, the dominant source of sediment to the basin is identified. This work then applies and tests different geochronological models for excess ²¹⁰Pb within the estuarine system, showing the strengths and weaknesses of each model application, and presents a method for applying tempestite horizons for increased resolution and accuracy of estuarine geochronologies. Finally, the established high-resolution multi-decadal geochronology, along with historical physical data obtained for the system, is used to identify sediment source and drivers of sediment transport within the estuary to the coastal ocean through time. This study identifies multiple sedimentation events that are triggered by conditions that have a recurrence interval of ~1 year (+/- 0.5). Through this multi-decadal record, sediment flushing events occur at a much more frequent interval than previously thought (i.e. annual rather than decadal time-scales), indicating the potential role annual moderate energy storms in addition to high-energy decadal to millennial storm events play in sediment erosion and transport through the estuary. This work advances our understanding of how storms impact sediment erosion, transport and deposition within and through the coastal zone, furthering our understanding into the role that climate change and more frequent, intense storms will play in sediment flux from estuaries to the coastal ocean.