RECONSTRUCTION OF LATE HOLOCENE HYDROCLIMATE AND ENVIRONMENTAL CHANGE IN SOUTHERN CENTRAL AMERICA WITH AN EMPHASIS ON THE TERMINAL CLASSIC DROUGHT (TCD)

In Central America, the Terminal Classic Drought (TCD) was defined by a series of moderate to severe droughts that took place between ~750 and 1100 CE. However, to-date, we have a limited understanding of how thermal conditions varied during the TCD and if changes in vegetation and hydrology were coeval with an altered thermal regime in this region. Lake sediment cores recovered from two, high-elevation, glacially-formed lakes in highlands of central Costa Rica, were analyzed for sub-fossil chironomids, charcoal and sediment geochemistry (C%, N%, δ¹³C, and C/N ratios). Variations in the abundance of chironomid indicator taxa, e.g. Procladius and Psectrocladius, in conjunction with increases in charcoal concentration and fluctuations in δ¹³C, indicative of the expansion of C₄ vegetation, suggest that the TCD (~830-1100 CE) in the central highlands of Costa Rica was characterized by an extended interval of cool, dry conditions and more frequent fires. The results of this study are used to assess the hypothesis that a cooling of the tropical Atlantic and a strengthened North Atlantic Subtropical High can provide a dynamical explanation for the multi-decadal droughts that characterizes the TCD interval in Central America.