Mathias Vuille, Douglas R. Hardy, Carsten Braun, Frank Keimig, Raymond S. Bradley

    Dept. of Geosciences, University of Massachusetts, USA

High-resolution proxy records from the tropics indicate considerable climatic variability during the Holocene. The understanding of these fluctuations is crucial in order to provide a longer-term perspective of recent climatic variations. Ice cores from low latitudes provide such high resolution information about past environmental conditions, as annual snow layers are compressed and preserved within the ice sheet. However in the past paleoclimatic reconstructions in the tropics have often suffered from an incomplete or doubtful interpretation of the proxy data, as climatic information, needed for calibration was not available.

We have addressed this problem in a joint effort with L. G. Thompson, (Ohio State Univ.), who drilled two ice cores in June - July 1997 on Nevado Sajama (18.1 S; 68.9 W; 6542 m), Bolivia. Since October 1996 an automatic, satellite-linked weather station provides us with hourly data from Sajama summit in near real-time. By sampling and analyzing individual stratigraphic snowfall layers, each event can be characterized in terms of its geochemical signals and the climatic situation before, during and after the snowfall. This will help us to establish a relationship between the climatic conditions and the geochemistry of the snow and thereby considerably improve the interpretation of the climatic signal in the ice core as preserved by variations of stable isotopes, water equivalent, dust and geochemistry.

However data from the weather station alone can not resolve large scale atmospheric circulation anomalies and air flow patterns that considerably influence the geochemistry of snow deposited on the summit of Sajama. Therefore additional large scale circulation analyses are carried out to detect source regions of precipitation and main trajectories of humidity transport.

Finally the analyses of upper-air circulation patterns over Sajama during the last decades as revealed by nearby upper-air soundings and precipitation data provide additional information for a calibration on a longer-term time scale. Emphasis is given to extreme dry and wet periods and to phenomena like ENSO, that can be detected in the uppermost stratigraphy of the ice core.

Return to UMass Bolivia

Climate & Snow Home Page

Document maintained by Doug Hardy (dhardy@geo.umass.edu)
Last updated: 1 October 1998
http://www.geo.umass.edu/climate/bolivia/agu97.html