Modern foraminiferal distribution and recent environmental change in core sound, north carolina, USA

Core Sound, a shallow, narrow estuarine lagoon located behind North Carolina's southern Outer Banks, was studied to document modern foraminiferal distributions and identify environmental changes during the past ca. 90 years. Seventy-six samples collected in 2004 were analyzed to establish the modern distribution and abundance of foraminifera. Cluster analysis defined four modern biofacies: Marsh (dominated by Trochammina inflata and Haplophragmoides wilberti), Estuarine High Salinity A (dominated by Ammonia parkinsoniana and Elphidium mexicanum), Estuarine High Salinity B (dominated by Ammonia parkinsoniana and Elphidium excavatum), and Estuarine Low Salinity (dominated by Ammotium salsum, Ammonia parkinsoniana and Elphidium gunteri). The four biofacies were also recognized by discriminant analysis. Comparison of the 2004 distributional data with those derived from samples collected in 1959 from central and eastern Core Sound revealed that Elphidium decreased while Ammonia increased in relative abundance. Other researchers have suggested that such a trend reflects increased eutrophicarion, although there is no independent evidence for this in Core Sound. The temporal comparison also showed that Quinqueloculina has become more widespread immediately adjacent to barrier islands, which might relate to an increase in subaquatic vegetation. Five short cores were taken in mainland bays on the western margin of Core Sound. Analysis of radionuclides (²¹⁰Pb and ¹³⁷Cs) provided a chronostratigraphic framework for two of the cores. To aid paleoenvironmental interpretations, foraminiferal data from core sediments dated as ca. 90 yr were entered as unknowns into the modern distribution discriminant analysis. Samples from mainland bay cores were classified with modern biofacies and indicated no significant foraminiferal change in the mainland bays over the last ca. 90 years.