HIGH RESOLUTION SPELEOTHEM PALEOCLIMATOLOGY OF NORTHERN VENEZUELA: A PROGRESS REPORT Luis A. GONZÁLEZ 1 & Roger GÓMEZ 2 1 The University of Kansas. Department of Geology. Lawrence, Kansas 66045 USA 2 The University of Iowa. Department of Geoscience. Iowa City, Iowa 52240 USA Recibido en Noviembre de 2002 ABSTRACT Stalagmites from four caves of northern Venezuela were collected for paleoclimatology studies. Preliminary age determinations and carbon and oxygen isotope data from a stalagmite, show a major stable isotope shift from approximately 11,500 to 10,000 years ago similar to the Sajama ice core record and the Cariaco basin foraminifera G. rubber record. The enriched δ 13 C and δ 18 O data at this period (relative to the Holocene data) suggest dryer conditions with either greater contribution of C4 plants or less recycling of soil CO 2 and colder conditions. Key words: Geochronology, speleology, El Niño Southern Oscillation, Inter Tropical Convergence Zone, stable isotopes. RESUMEN Paleoclimatología de alta resolución en espeleotemas del norte de Venezuela: Informe de progreso. En cuatro cuevas del norte de Venezuela fueron colectadas estalagmitas para estudios paleoclimáticos. Datos preliminares de edades y de isótopos de oxígeno y carbono de una de las estalagmitas, muestran un cambio brusco e importante de los isótopos estables aproximadamente entre 11.500 y 10.000 años, muy similar a los registros obtenidos en el núcleo de hielo de Sajama y en los foraminíferos G. ruber de Cariaco. El enriquecimiento de δ 13 C y δ 18 O en éste período relativo a los datos de Holoceno, sugiere condiciones más secas con, ya sea una mayor contribución de plantas C4, o un menor reciclaje del CO 2 del suelo y condiciones más frías. Palabras claves: Geocronología, espeleología, oscilación sur de El Niño, zona de convergencia intertropical, isótopos estables. INTRODUCTION The climate of Central America, the Caribbean islands (Antilles), and the northern part of South America is largely controlled by the position of the Inter Tropical Convergence Zone (ITCZ) and its interactions with the tropical Atlantic and Pacific Oceans (ENFIELD & ALFARO 1999). In this region anomalous rainfall patterns and the flooding and droughts that result from them, have been linked with El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation (e.g., HASTENRATH 1984, ENFIELD & ALFARO 1999, GIANNINI et al. 2000, 2001, CHEN & TAYLOR 2002). Climatic change during the last 20,000 years in Central America, the Caribbean, South America, and even changes in the intensity of the North American monsoon have bee attributed to long-term changes in the position and/or intensity of the ITCZ over South America, and changes in ENSO and NAO intensity (LIN et al. 1997, CURTIS et al. 1999, HAUG et al. 2001, BAKER et al. 2001, LEDRU et al. 2002 and many others). Because during the northern hemisphere summer the ITCZ resides over northern Venezuela, it is the best region to study the history of changes in the ITCZ over the last 20,000 years. Few paleoclimatic studies have been conducted in northern Venezuela as the marine sediments and fossils in the Cariaco basin (e.g., HAUG et al. 2001, LIN et al. 1997), and sediments and pollen from Lake Valencia (e.g., CURTIS et al. 1999), the Venezuelan Andes (e.g., RULL et al. 1987) and the Guayana Highlands (e.g., SCHUBERT et al. 1994). Thus, we have begun a study to provide a broader longitudinal and temporal coverage using stalagmite growth histories and the stable isotope compositions (carbon and oxygen isotopes) of the carbonate. METHODS During January 2002 and with the assistance of the Venezuelan Speleological Society (SVE) members, we sampled Fig. 1. Samples collected from caves along the northernmost reach of the ITCZ. All stalagmites were active at time of collection. Bol. Soc. Venezolana Espeleol. (36) 2002 27