1Dept. of Geosciences, University of Massachusetts, USA
2Byrd Polar Research Center and Dept. of Geological Sciences, The Ohio State Univ., Columbus
Ice-core records from low latitude, high-elevation sites provide valuable knowledge of past global change. To optimize the information within these proxy records, the climatic significance of intra- and interannual geochemical variations must be better established. At Nevado Sajama in Bolivia (6542 m, 18°06'S, 68°53'W), annual snowpack analyses and automated weather station measurements are supporting the interpretation of ice cores drilled through the summit ice cap in 1997. The analysis of comprehensive weather station data is closely tied to the results of annual snowpack studies carried out in the vicinity of the station. We delineate individual stratigraphic layers in the snow pits, and sample in detail for oxygen isotopic ratios (d18O), microparticles (dust), and major ion concentrations. This enables episodes of snowfall to be characterized in terms of precipitation geochemistry. The objective of these efforts is to better understand the atmospheric sources of geochemical variability in the snow, and thus to enhance interpretation of down-core geochemical variations within ice cores from the Tropics.
The first two years of measurements at the site (October 1996 to September 1998) represent opposite extremes in the context of current climate on the Altiplano, as determined by analysis of data (1968-95) from regional stations, NCEP reanalysis, and the ice core. The period of snow accumulation in 1996-97 (i.e. austral summer) was unusually cold and wet, while during 1997-98 precipitation in the region was greatly reduced, and temperatures were anomalously high. At the conclusion of each accumulation season, we analyzed the stratigraphy of the snowpack and recovered frozen snow samples. Contrasts in the climate system between the two years led to large differences in snow geochemistry. For example, relative to the previous years profile of d18O, the 1997-98 snowpack is 4.6 per mil more enriched (-12.6 vs. -17.2 per mil) and much less variable (std dev 1.8 vs. 4.9 per mil; range 6.4 vs. 19.5 per mil). Variations in snow geochemistry are discussed in the context of snowfall event stratigraphy and atmospheric characteristics through the important 1997-98 El Niño event and the year prior.
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