HISTORY OF PALEOENVIRONMENTAL CHANGES IN THE SOUTHWESTERN EVERGLADES (FLORIDA, USA) USING FORAMINIFERAL ASSEMBLAGES

This study examines temporal changes in benthic foraminiferal assemblages and habitat change over the past ~2200 years for the Everglades. South Florida’s low-lying coasts are fringed by marsh and mangrove environments, and subject to a microtidal regime. Additionally, the region is underlain by a highly porous aquifer, making the area highly sensitive to inundation and saltwater intrusion resulting from a rising sea level. Previous foraminiferal marsh studies in South Florida’s coastal mangrove environments are few, and a foraminifera-based paleoenvironmental study for this region has never been attempted. Even though mangrove forests comprise 70% of the world’s tropical and subtropical coasts, the responses of mangrove wetlands to sea level rise have not received the same scientific attention as salt marsh coasts in North America and Northwestern Europe.

We analyzed 27 samples from a 262-cm-long section of a sediment core which was retrieved about 4 km inland along the Shark River, and radiocarbon dated. We identified over 40 foraminiferal species, about half of which were agglutinated taxa. A stratigraphically constrained cluster analysis of the assemblages revealed groups that correspond to changing salinities, as well as zones identified in a previous pollen study. We found that calcareous taxa such as Ammonia parkinsoniana, Ammonia tepida, and Elphidium spp. dominate in the upper 10 cm of the core, which has the greatest marine influence and corresponds to a group separated from the lower assemblages by a constrained, unweighted pair group cluster analysis with average linkage. Other calcareous perforate taxa are present in low numbers below 31 cm in depth. Between 31 and 140 cm, assemblages contain agglutinated Trochammina inflata, Arenoparrella mexicana, Haplophragmoides wilberti, and Miliammina fusca. Below 140 cm, the latter is replaced by agglutinated Jadammina macrescens and Trochammina comprimata. Although the agglutinated species are considered high-marsh taxa, the cluster analysis distinguishes the assemblages below 140 cm as distinctly different, reflecting lower salinities. The shifts in benthic foraminiferal assemblages record the timing of sea-level increase over the last ~2200 years, which can serve as a prediction in habitat change for current rising seas.