THE ROLE OF HOLOCENE SEA LEVEL IN SHAPING SOUTH FLORIDA ENVIRONMENTS

South Florida is a mosaic of distinctive environments including freshwater wetlands, mangrove coasts, shallow carbonate lagoons, and coral reefs that are part of the Greater Everglades Ecosystem, and they serve as critical habitat for endangered species. These environments developed throughout the Holocene and were shaped by the underlying geology, topography, climate, sea level, and foundational species (eg. mangroves, coral). Understanding how these components have interacted over time to alter these environments in response to changing sea level will provide information for resource managers seeking to restore and protect the fragile Everglades ecosystem under changing 21^st century conditions.

To obtain this information, we focused on mangrove fringed islands in Florida Bay, part of Everglades National Park. The interior of these islands are open carbonate mudflats that primarily lie below sea level and most do not have open exchange of water with Florida Bay. Eighteen cores were collected in 2014 from 4 islands located on an east-west transect across the Bay. Most of the cores reached the Plio-Pleistocene bedrock. To date, we have obtained 41 radiocarbon dates on 9 cores to resolve the timing of initial flooding of the south Florida platform, and we are using pollen, mollusks and d¹³C to determine depositional environments. Three islands exhibit a similar sequence: 1) basal freshwater peats, deposited in proximity to the paleo-shoreline; 2) inner to middle estuarine carbonate muds; 3) mangrove peat overlying the estuarine deposits, indicating formation of the island; and 4) micritic muds formed on mudflats. The fourth island, Bob Allen Key (BAK), illustrates the potential role of minor differences in bedrock topography in influencing the environment. The basal unit at BAK represents a freshwater marl prairie, overlain by a nearshore mangrove peat, which transitions to island mudflat deposition. Based on the preserved record, it appears that BAK has not been submerged during the last 5000 years. Additional analyses of these cores will provide a better understanding of the driving factors influencing formation of south Florida’s environments and provide resource managers with information to guide protection of the habitats and species in response to anticipated 21^st century change.