GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 223-9
Presentation Time: 3:55 PM


VERLAAK, Zoë R.F., Department of Earth and Environment, Florida International University, Miami, FL 33199 and COLLINS, Laurel S., Dept. Earth and Environment, Florida International University, Miami, FL 33199

This study is the first to examine the history of paleoenvironments and habitat change over the past ~3400 years for the Everglades, as interpreted from benthic foraminiferal assemblages preserved in a sediment core and the ecology of extant foraminifera in the region. The Everglades are one of the largest subtropical wetlands with dense mangrove forests extending over 80 km along the low-lying, microtidal coastline of South Florida. As this region is underlain by a highly porous aquifer, it is highly sensitive to inundation and saltwater intrusion due to a rising sea level.

Twenty-seven samples were analyzed from a 262-cm-long section of a radiocarbon-dated sediment core which was retrieved about 4 km inland along the Shark River Estuary. In total, 51 foraminiferal species were identified, the majority of which were calcareous taxa. Eighty-four percent of the taxa were also found in the distribution of modern assemblages across the Everglades. The modern study: 1) established that the modern analog to be used is the upper 2 cm of sediments, 2) indicated the organic carbon and salinity preferences of some common species, and 3) expanded the known taxonomic diversity for this area by 37%.

A stratigraphically constrained cluster analysis of the core’s assemblages revealed groups that correspond predominantly to changing salinities. Low-diversity, high-dominance assemblages indicate environments with extreme physical conditions for foraminifera, such as exists at the landward edge of the mangrove zone. An upper mangrove, lower mangrove and coastal habitat were recognized, as well as two transitional zones. The assemblage shifts over time are related to increasing salinity caused by sea level rise. Major changes occurred at ~3449 cal yrs BP, ~3244 cal yrs BP, ~1288 cal yrs BP, AD 1950, and AD 1982. The timing of the foraminiferal assemblage shifts indicates that the rate of habitat change was substantially faster after AD 1950. This corresponds well to the historic data collected from tide gauges in the region. The results of this study predict that changes in the coastal habitats will most likely continue at that same rate in the future, a conclusion of significance to South Florida’s growing coastal population and the ongoing rehabilitation of the Everglades ecosystem.