Establishing a Chronology of Late Quaternary Glacial Advances in the Cordillera de Talamanca, Costa Rica

Little research has focused on glacial events in the tropics. Providing an absolute glacial chronology in Costa Rica will build a foundation for future glacial chronologies and paleoclimate reconstructions in the highlands of Central America. Evidence of past glaciation, including moraines and glacial lakes, is preserved within formerly glaciated valleys in the Cordillera de Talamanca. Orvis and Horn (2000) constrained deglaciation ages of the most recent glacial event in the Cordillera de Talamanca based on radiocarbon dates of glacial lake sediments. Radiocarbon ages indicated complete deglaciation after 12.4 ka cal BP but before 9.7 ka cal BP (Orvis and Horn, 2000). This research aims to date the formation ages of moraines using cosmogenic 36Cl [chlorine-36] surface exposure dating. Exposure ages provide absolute age constraints on the timing of glacial events within the Cordillera de Talamanca, Costa Rica. Cosmogenic 36Cl exposure ages indicate a Last Glacial Maximum (LGM) event ~21–18 ka, which is synchronous with the global LGM. Ages also indicate periods of glacial retreat and stillstands ~18–10 ka. An elevation and age comparison suggests similar timing and extent of LGM advance between two valleys on opposite sides of the mountain range. These results improve understanding of the timing of glacial events in the tropics, which is of critical importance for reconstructing regional and global climate patterns.