2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 3
Presentation Time: 8:00 AM-6:00 PM

Isotopic Evidence for Climate Change during the Vandal Minimum, Southwest Florida, US

WANG, Ting, Geological Sciences, University of North Carolina, 104 South Road, CB #3315, Chapel Hill, NC 27599, SURGE, Donna, Geological Sciences, University of North Carolina at Chapel Hill, 104 South Road, CB #3315, Chapel Hill, NC 27599 and WALKER, Karen Jo, Florida Musem of Natural History, Univ of Florida, Museum Road & Newell Drive, PO Box 117800, Gainesville, FL 32611-7800, twang@email.unc.edu

The Vandal Minimum (VM) climate episode is so called because it occurred in Europe between 500-800 AD, concurrent with the Vandal invasion of the Roman Empire. This climate episode was first documented in European proxy records as cold and dry with increased frequency of severe weather. Archaeological evidence from coastal southwest Florida suggests this region and its local inhabitants (the Calusa) were affected by VM climate conditions. Drought and cooling may have been responsible for the abandonment of Calusa sites by 750 AD. To test this hypothesis, we reconstructed climate conditions at seasonal time scales using the oxygen isotope temperature proxy (δ18O) preserved in Mercenaria campechiensis shells and Ariopsis felis otoliths. We compared our climate reconstructions with archaeological data to answer the following questions: How long did the cooling/drought last and how severe were these conditions? How much coherency does the paleoclimate record share with the archaeological evidence?

Previous investigation demonstrated the strength of using a multi-taxa approach (combining records from M. campechiensis shells and A. felis otoliths) to reconstruct conditions in an estuarine environment as is the case here. Comparing δ18O records from both species allowed us to reconstruct relative cool versus warm and wet versus dry conditions. Eight shells and four otoliths representing the entire stratigraphic extent of the VM were selected for isotopic analysis and microsampled at submonthly resolution. The δ18O time series from the otoliths and shells indicated the winters and summers in the beginning of the VM were relatively warm and wet (similar to today). Winter temperatures cooled by 1-2°C in the mid VM, and summers were relatively dry. The late VM had winter temperatures similar to today and dry summers. Our climate reconstructions based on isotopic data are in good agreement with archaeological observations and with the cool and dry conditions documented in Europe.