Distribution of foraminifera in Pamlico Sound, North Carolina, over the past century

Foraminiferal and radionuclide data have been used to investigate environmental change that has occurred within Pamlico Sound, North Carolina, over the last century. Environmental conditions were evaluated for three time slices; (1) the modern environment as determined by surficial (0-1 cm) sediments, (2) short-core intervals representing approximately 40 years BP, as determined by Cs-137 activity, and (3) short-core intervals representing approximately 120 years BP, as determined by Pb-210 activity. Cluster analysis distinguished four foraminiferal assemblages at the surface (0-1 cm): (1) Marsh Biofacies, (2) Estuarine Biofacies A, (3) Estuarine Biofacies B, and (4) Marine Biofacies. The Marsh Biofacies is characterized by typical marsh foraminifera such as Tiphotrocha comprimata, Trochammina inflata, Miliammina fusea and Haplophragmoides wilberti. Estuarine Biofacies A is distinguished from Estuarine Biofacies B by the greater relative abundance of the agglutinated species Ammotium salsum and Ammobaculites crassus in the former and the greater relative abundance of Elphidium excavatum in the latter. The Marine Biofacies is comprised completely of calcareous foraminifera (e.g., Elphidium excavatum, Hanzawaia strattoni, Cibicides lobatulus, Elphidium subareticum, Quinqueloculina seminula and Elphidium galvestonense) and is restricted to tidal inlets. Down-core foraminiferal data indicate that approximately 120 years BP, Pamlico Sound was dominated by Estuarine Biofacies A, which is indicative of brackish conditions. Upcore in the 40 years BP and modern time slices, Estuarine Biofacies B is the more prominent assemblage within Pamlico Sound; this is indicative of increased salinity over time. Lowered salinity conditions 120 years BP may be the result of high hurricane activity over a several year period.