COSMOGENIC NUCLIDE CONSTRAINTS ON LATE QUATERNARY GLACIAL ADVANCES IN THE CORDILLERA DE TALAMANCA, COSTA RICA

Extensive studies on paleoglaciation have been conducted in the middle and high latitudes, but less is known about paleoglaciation in tropical highlands. Constraining the timing and extent of past glacial advances in the Cordillera de Talamanca, Costa Rica, offers unique insight into paleoclimates of the equatorial tropics. In the Valle de las Morrenas near Cerro Chirripó (3819 m), Costa Rica’s highest peak, Orvis and Horn (Quaternary Research, 2000) identified four moraine complexes (Chirripo I-IV). The Chirripo IV glacier, the largest mapped, indicated wetter and colder conditions than the Chirripo II and III glaciers. Here we present absolute ages for moraines on Cerro Chirripo based on cosmogenic ³⁶Cl nuclide surface exposure dating. Ages show scatter but suggest an old and large glacial advance down valley >40 ka (Chirripo IV). A second set of younger moraines (Chirripo III) suggest a less extensive advance and retreat ~10 ka. Ages from moraines closest to the Chirripo headwall (Chirripo II and I) are slightly scattered but also indicate retreat ~10 ka. The similar ages of these moraine complexes may be due to rapid glacial retreat ~10 ka. Our results suggest a pre-LGM glacial advance down valley followed by less extensive advances during the LGM and Younger Dryas. By constraining the timing of glacial events in Costa Rica, regional and global climate patterns can be better understood.