Abstract

Ice core records from tropical and subtropical ice caps provide unique information about the chemical and physical character of the atmosphere. Seasonal variations in the chemical composition of the snowfall and amount of precipitation accumulating on these ice caps produce annual laminations that allow these stratigraphic sequences to be dated. The thickness of an annual lamination reflects the net accumulation, while the physical and chemical constituents (e.g., dust, δ18O, various ions) record atmospheric conditions during deposition. The information presented in this chapter builds upon an earlier investigation of the preservation of an El Niño/Southern Oscillation (ENSO) history in the 1,500-year record from ice cores recovered from the Quelccaya ice cap, Peru (Thompson et al. 1992).

Recent ice cores from Nevado Huascarán, Peru (90°7′S, 77°37′W, 6,048 m), which provided the first tropical ice core history extending back to the Late Glacial Stage (Thompson et al. 1995), also contain an annually resolvable record for the past 270 years. This study is based upon the most recent 68-year period from the Huascaran ice cores, from which a methodology for isolation of ENSO events is developed.

The Quelccaya ENSO study (Thompson et al. 1992) revealed that in the Peruvian Andes the ice core constituent most highly correlated with sea surface temperatures (SSTs) is δ18O(r = 0.36, significant at the 95% level).