2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 134-7
Presentation Time: 9:00 AM-6:30 PM


GERLACH, Matthew J., Geosciences, University of Rhode Island, 9 East Alumni Ave, Kingston, RI 02881, ENGELHART, Simon E., Department of Geosciences, University of Rhode Island, Woodward Hall, 9 East Alumni Avenue, Kingston, RI 02881, KEMP, Andrew C., Department of Earth and Ocean Sciences, Tufts University, Medford, MA 02155, MOYER, Ryan P., Florida Fish and Wildlife Conservation Commission, Florida Fish and Wildlife Research Institute, 100 Eighth Avenue SE, St. Petersburg, FL 33701, SMOAK, Joseph M., Department of Environmental Science, Policy and Geography, University of South Florida, 140 7th Ave S, St. Petersburg, FL 33701 and BERNHARDT, Christopher, U.S. Geological Survey, 12201 Sunrise Valley Drive, MS 926A, Reston, VA 20192, mgerlach@my.uri.edu

Late Holocene relative sea-level (RSL) reconstructions provide information on how sea level has responded to past climate variation and serve as a baseline for contextualizing projected sea-level rise over the coming decades. To address a spatial gap in late Holocene RSL data on the eastern margin of the Gulf of Mexico, we present the results of a high-resolution (decadal to centennial age errors; cm to dm vertical errors) sea-level reconstruction based on the sediment record of a southwestern Florida salt marsh at the Little Manatee River, in eastern Tampa Bay. The chronology for our selected ~1.25m core was developed using AMS radiocarbon dating of in-situ plant macrofossils, Pb210, Cs137 and pollution and pollen chronohorizons. We use the combined chronological markers to construct an age-depth model using Bchron that reveals RSL changes over the past ~2100 years.

Lithostratigraphic analysis reveals salt-marsh peat began to accumulate on top of an organic sandy-silt that serves as the basis for the salt-marsh platform throughout the study site. The sub-surface peat contains abundant Juncus roemeranius macrofossils except for a 0.30 m interval located at a depth of 0.45 - 0.75 m. Vertically zoned assemblages of foraminifera are employed as sea-level indicators to reconstruct RSL. Foraminiferal analysis reveals distinct changes in fauna throughout the core. The bottom 0.25 m of recovered sample is dominated by Ammobaculites spp. and Miliammina fusca. An assemblage composed of Arenoparella mexicana, Ammoastuta inepta and Haplophragmoides wilberti is the major component of the remaining 1.00 m of core, except for a 0.20 m section occurring at a depth of 0.45 - 0.65 m. In this interval, the low marsh and tidal flat species Ammobaculites spp. increase to ~20% abundance with an associated decline in high-marsh species indicating RSL rise outpaced sediment accumulation during this time.

Reconstructed RSL from this study will be evaluated against late Holocene sea-level records from sites farther north on the U.S. Atlantic Coast (Northern Florida, North Carolina, New Jersey, Connecticut) and the U.S. Gulf Coast (Louisiana) to identify potential mechanisms causing presence/absence and non-synchronous sea-level oscillations during the Common Era.