Isotopic evidence for climate change during the Vandal Minimum from Ariopsis felis otoliths and Mercenaria campechiensis shells, southwest Florida, USA

Archaeological evidence from coastal southwest Florida suggests this region and its local inhabitants (the Calusa) were affected by drought and cooling during the Vandal Minimum climate episode (AD 500-800). To test this hypothesis, we reconstructed seasonal-scale climate conditions using stable oxygen and carbon isotope ratios (delta O-18 and delta C-13) preserved in Ariopsis felis otoliths and Mercenaria campechiensis shells. Comparing delta O-18 records from both species distinguishes between cool versus warm and wet versus dry conditions. delta O-18 values from four otoliths indicate cooling of winter temperatures occurred in the early Vandal Minimum (AD 500-600) and late half of the middle Vandal Minimum (AD 650-700). Persistent dry summers punctuated by occasional years with wet summers throughout the Vandal Minimum were detected from delta O-18 values of eight archaeological shells. Our climate reconstructions are in good agreement with archaeological observations and with the cool and dry conditions documented in Europe.