The utility of estuarine settling basins for constructing multi-decadal, high-resolution records of sedimentation

Abstract

Obtaining long-term records of sediment flux and sources to estuaries is a major challenge in coastal and estuarine research due to the dynamic processes that actively work to remove the high-resolution, long-term sediment record. Examining cores from sediment-settling basins directly adjacent to or within estuarine systems provides a potential alternative means of establishing a history of estuarine sedimentation. As a recently established settling basin with high rates of sedimentation, Cape Lookout Bight, NC presents an ideal coastal environment to capture a long-term record of sedimentation.In 2010, a 4.6 m-long core was extracted from the deepest portion of the basin. Through lithologic description, grain-size, water content and radioisotope analysis (excess 210Pb), a high-resolution geochronology of sedimentation has been established for the basin. The record begins with spit accretion that captured part of the marine shelf and formed the basin. A transition in sediment type from dominantly marine, through storm-induced overwash, to dominantly estuarine was identified in the basin. This transition reflects the increased trapping efficiency of fine estuarine mud due to the changing geomorphology of the settling basin. An abrupt increase in the rate of estuarine sedimentation occurred ∼1983–1985. After careful reconstruction of basin geomorphology, this increased rate of sedimentation is not attributed to internal dynamics within the basin, but instead is interpreted to be the result of increased estuarine sediment flux through Barden's Inlet from the upper estuary. This work underscores the importance of considering changing basin physiography and sediment dynamics before interpreting the paleo-record, as those mechanisms can hide or eliminate allogenic signatures from the sediment profile.