A High-Resolution Speleothem Climate Record for the Past 5.2ky From Western Costa Rica

The El Niño Southern Oscillation (ENSO) is the most important source of interannual climate variability in the tropics today. While some data suggest that the frequency of strong ENSO events has apparently increased through the Holocene (e.g. Rodbell et al., 1999), these studies need corroboration and a thorough understanding of ENSO variations over the Holocene remains a goal of paleoclimate studies. In Central America, meteorological data show that El Nino events are associated with decreased rainfall relative to normal or La Nina years, and that rainfall amount is strongly anti-correlated to rainfall \delta¹⁸O via an amount effect. Isotopic studies of stalagmites in other regions have shown their utility in studying changes in precipitation and here we apply these techniques to study Central American climate variation and by inference changes in mean ENSO state on sub-decadal timescales. Stalagmite CN-1 was recovered from Nicoa Cave in Barra Honda National Park located on the Nicoya Peninsula in Costa Rica, on the western side of Central America. An age model for CN-1 was constructed using 7 U/Th measurements and indicates continuous deposition from 5200 y B.P. to present. A preliminary oxygen and carbon isotope data set covers the past 1500 y at 6 year resolution. Ultimately we will cover the past 5.2 ky at similar resolution. The isotopic values range greatly, from -6.5 to -10.2 \permil for \delta¹⁸O, and from -4 to -10.5 \permil for \delta¹³C. More depleted values are interpreted to be indicative of wetter periods and periods of less-frequent strong ENSO events. A preliminary comparison of the CN-1 isotope record with the Lake Pallcacocha ENSO record shows a good match between more enriched isotope values and periods of more frequent strong El Nino events, particularly for \delta¹³C. The data also show a strong multidecadal-scale cyclicity.