Understanding Estuarine Ravinement Processes at Monthly to Decadal Time Scales Through High-Resolution Geochronologies

Abstract

Estuaries and adjoining fringing marshes play a critical role in the nearshore sediment-transport system. Coastal fringing marshes are eroding and watershed-sediment flux is changing globally, largely as a result of increased sea-level rise, storminess and anthropogenic modifications. A better understanding of how estuarine shorelines will respond to these impacts and will modify coastal sedimentation will improve the coastal component of source to sink models and increase coastal sustainability. Previous research has shown that estuarine shorelines are very susceptible to erosion from impacts of accelerated sea-level rise and storms. However, these studies often lack the resolution to determine how these forcing mechanisms will impact the coastal zone over time. Sediment cores from mini-basins directly adjacent to the estuary provide an alternative for establishing high-resolution, long-term estuarine geochronologies. As a recently-established mini-basin with historically high rates of sedimentation, Cape Lookout Bight, NC presents an ideal coastal environment to capture a high-resolution record of sedimentation over the last century. A 4.6 m long core was extracted from the deepest portion of the basin. Through lithologic description, grain-size and radio-isotope analysis (excess 210Pb) conducted at 1-cm intervals, a sediment accumulation rate has been interpolated on a monthly basis over a 40 year record. This record has been compared through time-series analysis to historical climate and sea-level records for the area. Modeling the data in this way identifies the relative impact each forcing mechanism (i.e. sea-level, wind, precipitation, waves) had on coastal sediment erosion on event, seasonal, annual, and decadal time-scales. This study links erosional processes in the estuary directly with sediment flux to the continental shelf, taking advantage of the sediment trap at the Bight. Sediment flux is directly related to wave energy and water level and is not related to variations in sediment contribution from small coastal-plain watersheds. This study will provide insight into the relative impact different forcing mechanisms like sea-level rise and storminess have on estuarine erosion, advancing our understanding of how climate change will impact the coastal zone, and aiding in the development of more robust models of coastal change.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017