Analysis of the chronological data and observation of a lagoonal sediment core reveal sand washover events between around 2.4 to 2.5 cal. ky BP in the Isumi River lowland. We conducted radiocarbon dating with AMS and constructed an age-depth model using the latest calibration curve and appropriate model routine. In the middle to lower part of the core, dark-gray sand layers are repeatedly deposited. Sand layers may exhibit an erosional surface at the base with fining upward grading. The overwash layers are composed of well-rounded sand with occasional gravel, indicative of transportation. overwash sediment characteristics are consistent with proximal marine deposits, suggesting an ocean origin (though riverine sediment is also similar in character). The age-depth model indicates very high sediment accumulation rates associated with overwash deposits. Based on the amount of accumulated sediment, relatively large-scale redeposition events occurred during this period but more information is needed to constrain the mechanism(s) causing the events. We also present a local reservoir age correction compatible with the Marine20 calibration curve.

We present here the first high-resolution pollen record of vegetation response to interactions of hurricane and fire disturbances over the past 1200 yr from a small lake in Alabama on the Gulf of Mexico coast. The paleo tempestological record inferred from the over wash sand layers suggests that the Alabama coast was directly struck by Saffir–Simpson category 4 or 5 hurricanes twice during the last 1200 yr, around 1170 and 860 cal yr BP, suggesting an annual landfall probability of 0.17% for these intense hurricanes. The charcoal data suggest that intense fires occurred after each of these hurricanes. The pollen data suggest that populations of halophytic plants (Chenopodiaceae) and heliophytic shrubs (Myrica) expanded after the hurricane strikes, probably due to saltwater intrusion into the marshes and soil salinization caused by over wash processes. Populations of pines (Pinussp.) decreased significantly after each intense hurricane and the ensuing intense fire, suggesting that repeated hurricane–fire interactions resulted in high tree mortality and probably impeded recruitment and recovery. Our data support the hypothesis that the likelihood and intensity of fire increased significantly after a major hurricane, producing responses by vegetation that are more complex and unpredictable than if the disturbance agents were acting singly and independently.