Date of Award
Doctor of Philosophy
Sally P. Horn
Henri D. Grissino-Mayer, David G. Anderson, Chad S. Lane
We use multiple proxies from sediment cores to identify periods of climate stress during the late Holocene across the circum-Caribbean region and to determine how fire activity and signals of Pre-Columbian agriculture coincide with these arid periods. We examine evidence of aridity from stable carbon isotope ratios and shifts in elemental composition, along with pollen and microscopic charcoal, at Bao Bog in the highlands of Hispaniola. We infer two major periods of aridity (3600–2300 and 1040–850 cal yr BP), with the later period associated with the late phase of the Terminal Classic Drought. A third, less marked interval of aridity corresponds to the Little Ice Age from 550–100 cal yr BP. Southward shifts in the mean latitudinal position of the Intertropical Convergence Zone coincide with the arid periods in the Bao Bog record, which we interpret as also coinciding with a lowering of the elevation of the Trade Wind Inversion.
We also produce three new records that show environmental change, maize agriculture, and fire history in southern Pacific Costa. Our 4300-year record from Laguna Los Mangos shows the earliest evidence of Zea mays subs. mays in the region at ca. 3300 cal yr BP, following a 1000-year period when the area around the lake was largely forested, with slight or no agricultural activity. The Laguna Los Mangos record contains evidence of the transition to maize agriculture and a later decline associated with the onset of the LIA and Spanish contact. From Laguna Danta and Laguna Carse we developed high-resolution records of fire history and maize agriculture spanning the Little Ice Age. We found that fires occurred during the Little Ice Age and were influenced by human activity related to agriculture, but that fires persisted following agricultural decline, suggesting climate as a driver of fire in the lowlands. The continuation of fire into the Little Ice Age contradicts a recent global synthesis of fire activity and suggests local variability in fire response to climate.
Johanson, Erik Nicholas, "Reconstructing Late Holocene Fire, Agriculture, and Climate from Sediment Records in Costa Rica and the Dominican Republic. " PhD diss., University of Tennessee, 2016.