Variability of snow accumulation and isotopic composition on Nevado Sajama, Bolivia

Abstract

High‐elevation ice caps develop an archive of atmospheric constituents and properties through the accumulation of snowfall. The timing of precipitation events, therefore, fundamentally governs the environmental information that ice core records can provide. These events are often highly seasonal, as are various postdepositional processes influencing the snow's physical and chemical properties. Knowledge of climatic conditions at an ice core site is essential to a full understanding of the ice core record. This work reports on 4 years of meteorological measurements near the summit of Nevado Sajama, an ice‐capped peak rising ∼2500 m above the South American Altiplano (elevation 6542 m), from which a 25,000‐year ice core record was recovered in 1997. On‐site measurements were combined with National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis results and Altiplano station data to reconstruct 50‐year time series of air temperature, snowfall, and net accumulation at the summit. These time series were examined in the context of the Sajama δ18O profile over the same time interval. A strong relationship exists between Sajama δ18O and precipitation; both snowfall and net accumulation explain nearly half of the isotopic variance. In contrast, no significant association exists between air temperature and δ18O over this time period. The Sajama ice core record represents a relatively short proportion of time centered on the months of January or February, when net accumulation takes place, and cannot be interpreted in terms of annual mean conditions. On Sajama, interannual δ18O variability provides a sensitive measure of interannual precipitation variability, closely tied to ENSO and conditions in the equatorial Pacific Ocean.