THE INFLUENCE OF SEA LEVEL, CLIMATE, GEOLOGY AND HUMANS ON SOUTH FLORIDA ECOSYSTEMS

The carbonate platform of south Florida contains distinctive ecosystems that include the Everglades wetlands, an extensive mangrove coastline, and the Florida Keys reef tract. The current ecosystems have evolved throughout the Holocene – a product of geology, climate, and sea level. Currently, the Greater Everglades Ecosystem is the focus of a 30-year restoration effort, and as restoration proceeds it is essential for land managers to understand the relative roles of natural forces and anthropogenic factors in shaping the ecosystem. Understanding these ecosystem drivers is especially important given the predicted impacts of sea level rise and climate change on south Florida in the near future.

To better understand past ecosystem responses to forcing factors, we collected 18 cores from 4 mangrove-fringed islands in Florida Bay in 2014. The interiors of the islands are open mud flats that lie primarily below sea level and are generally isolated from Bay waters. These conditions provide an ideal setting for preserving a record of sea-level changes, storm history, and island formation. We reached the Plio-Pleistocene bedrock in most of the cores, providing us with a relatively complete sedimentary record from each island. The islands show a similar sequence. 1) Basal freshwater peats deposited ~3100-4900 years before present (ybp); these dates are consistent with previously published ages of ~5500 ybp for the onset of flooding of the south Florida platform. 2) Basal peats are overlain by carbonate sediments that contain abundant estuarine fauna, similar to modern Bay sediments. 3) Many of the cores contain a younger mangrove peat ranging from 2800 to 1300 ybp that overlies the estuarine sediments; these peats indicate the initial phases of island formation. 4) The uppermost section of all cores consists of carbonate mud with only scattered shells, which is representative of island deposition. Intermittent concentrated shell layers may mark storm deposits.

Analysis of these cores is providing information about past responses of the south Florida ecosystem to rising sea level, and potentially the role of storms in island formation. This understanding of past responses may allow land management agencies to anticipate and predict future responses to changing conditions.