ISOTOPIC EVIDENCE FOR EPISODIC MARINE WATER INCURSIONS INTO PAMLICO SOUND, NC DURING THE HOLOCENE

There have been several rapid climatic changes (RCCs) identified during the Holocene, concomitant with general global warming and sea-level rise. The North Carolina estuarine system is a prime location to look at the effects of these RCCs on coastal systems. After the initial flooding of the late Pleistocene river drainage, the Tar River and Pamlico Creek estuaries were formed at approximately 9000 cal yr BP. As sea level continued to rise, the area became completely flooded by 7000 cal yr BP; at this time barrier islands formed and enclosed Pamlico Sound resulting in estuarine conditions. After the initial formation, the Outer Banks barrier island system suffered periods of extreme segmentation resulting in deposits comprising normal marine salinity foraminifera within Pamlico Sound. Two of these periods occurred from approximately 4100 to 3700 cal yr BP and from 1200 to 500 cal yr BP, and correlate with RCCs. Segmentation of the islands allowed for elevated salinity conditions associated with altered hydrodynamics within the sounds. In order to test the impact of barrier segmentation on hydrodynamic conditions, we are analyzing δ¹³C and δ¹⁸O in 142 samples (9-10 foraminiferal specimens/sample) at 4 cm resolution within cores to provide an estimate of the marine influence in this area on decadal timescales. Error estimates are calculated by analyzing triplicate samples every 20 cm. Experiments revealed that the higher number of foraminiferal specimens (9-10) used per sample resulted in the smaller standard deviation for both δ¹³C (0.68) and δ¹⁸O (0.21). The target species is Elphidium excavatum since comparative analysis showed a significant offset between species (E. excavatum and Ammonia tepida). This high-resolution study is part of a larger study that includes geophysics, organic geochemistry, sedimentology, micropaleontology, inorganic geochemistry, and hydrodynamic modeling to understand the Holocene evolution of this system in response to climate, sea-level, and geomorphic changes.