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Tropical response to the 8200 yr B.P. cold event? Speleothem isotopes indicate a weakened early Holocene monsoon in Costa Rica

¹ Department of Geoscience, MS-4010, University of Nevada, Las Vegas, Nevada 89154, USA
² Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA
³ Department of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003-9297, USA
⁴ Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
⁵ Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA
⁶ Department of Earth Sciences, 204 Heroy Geology Laboratory, Syracuse University, Syracuse, New York 13244, USA

A ¹⁸O monsoon rainfall proxy record from a U-Th–dated Costa Rican stalagmite (8840–4920 yr B.P.) documents an early Holocene dry period correlative with the high-latitude 8200 yr B.P. cold event. High ¹⁸O values between ca. 8300 and 8000 yr B.P. demonstrate reduced rainfall and a weaker monsoon in Central America. A relatively wetter and more stable monsoon was established ca. 7600 yr B.P. The early Holocene dry event suggests a tropical-extratropical teleconnection to the 8200 yr B.P. cold event and a possible association of isthmian rainfall anomalies with high-latitude climate changes. The likely source of such a tropical anomaly is a decrease in Atlantic thermohaline circulation and atmospheric perturbations associated with drainage of proglacial lakes and freshwater discharge into the North Atlantic. A weaker monsoon at 8200 yr B.P. may be linked to wetland contraction and a decrease in methane observed in Greenland ice cores.

Key Words: Costa Rica • tropics • paleoclimate • 8200 yr B.P. event • stalagmite • ¹⁸O • Holocene • Central American monsoon • Intertropical Convergence Zone • U-Th dating

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