Late Holocene hydroclimate variability in Costa Rica: Signature of the terminal classic drought and the Medieval Climate Anomaly in the northern tropical Americas

Abstract

Abstract In the northern tropical Americas (Neotropics), notable hydrological variability has been documented in multi-proxy paleoclimate records between ∼600 and 1200 CE. This interval generally overlaps with the Maya Terminal Classic Drought (TCD: ∼770–1100 CE) and the Medieval Climate Anomaly (MCA: ∼950–1250 CE). There is, however, limited paleoclimate data that provide reliable estimates of terrestrial thermal variability in southern Central America during this time. In this study, we present chironomid-based temperature reconstructions, developed from sediment cores from two lakes: (1) Lago Morrenas 3C, a high-elevation glacial lake located on the crest of the Atlantic slope of the Cordillera Talamanca, Costa Rica, and (2) Laguna Zoncho, a mid-elevation lake located on the Pacific slope in southern Costa Rica. Distinctive shifts in the chironomid assemblages occurred at both sites between ∼610 and 1230 CE. These changes are inferred to reflect an ∼600-year interval characterized by depressed mean annual temperatures at Lago Morrenas 3C and dry conditions and lake level decline at Laguna Zoncho. Taken together, the multi-proxy paleoclimate records from these two lakes, including stable carbon isotope (δ13C) and charcoal data, suggest that middle elevations on the Pacific slope and high elevations on the Atlantic slope of Costa Rica experienced sustained drought, and possible cooling coeval with the TCD-MCA interval. The timing of hydroclimate variability in these records provides support for the hypothesis that cooling and drought in the northern tropical Americas during the TCD and early MCA were linked to thermal changes in the tropical North Atlantic.