Late Holocene hydroclimate variability in Costa Rica: Signature of the Terminal Classic Drought and the Medieval Climate Anomaly in the northern tropical Americas

Authors: Jiaying Wu*, Florida International University, David F Porinchu, University of Georgia, Sally P Horn, University of Tennessee
Topics: Paleoenvironmental Change, Climatology and Meteorology, Biogeography
Keywords: paleoclimate, chironomids, thermal variability, sediment geochemistry, climatic mechanism, tropical Americas, tropical North Atlantic, late Holocene
Session Type: Paper
Day: 4/4/2019
Start / End Time: 1:10 PM / 2:50 PM
Room: Coolidge, Marriott, Mezzanine Level
Presentation File: No File Uploaded


In the northern tropical Americas notable hydrological variability has been documented between ~600 and 1200 CE, an interval that overlaps with the Terminal Classic Drought (TCD: ~770-1100 CE) and the Medieval Classic Anomaly (MCA: ~950-1250 CE). However, limited paleoclimate records from this region have provided reliable thermal estimates during the TCD and MCA intervals. In this study, we present chironomid-based reconstructions of thermal conditions developed for two lakes in southern Central America: (1) Lago Morrenas 3C, a high-elevation glacial lake located east of the crest of Cordillera Talamanca in central Costa Rica, and (2) Laguna Zoncho, a mid-elevation lake located along the Pacific slope in southern Costa Rica. Distinctive shifts in the chironomid assemblages occurred at Lago Morrenas between ~610 and 1180 CE, reflecting a ~600-year lasting cool period. The absence of chironomid remains at Laguna Zoncho between ~730 and 1110 CE, reflects the occurrence of a negative hydroclimate anomaly resulting in greatly reduced lake level. Increasingly enriched stable carbon isotope (d13C) values observed at both sites between ~700 and 1100 CE indicate the expansion of C4 plants associated with dry habitats, provides additional evidence for the synchronous decrease in regional effective moisture. The nature and timing of the hydroclimate variability evident in these records from Costa Rica provide support for the hypothesis that the TCD and early MCA intervals in the northern tropical Americas are characterized by decreased effective moisture and depressed terrestrial air temperature and that these changes may be linked to thermal variability in the North Atlantic.

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