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

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.