Interpreting Climate Signals from a Shallow Equatorial Core: Antisana, Ecuador

Abstract

The potential use of equatorial glaciers to record past climates and precipitation sources in ice cores is unknown. A shallow (16-meter) core was recovered from the summit of Antisana in November of 1999 to evaluate whether it was worthwhile to drill a full-depth ice core with more rigorous post-collection processing. Ice lenses were found in the top 200 cm, all with a thickness less than 1 cm, suggesting occasional melt at the snow surface but little redistribution of water isotopes by percolating liquid water. Density in the core below the seasonal snow accumulation ranged from 450–720 kg m-3, indicating that we sampled the firn layer but not ice. The 18O content of the core ranged from a minimum value of -23.4‰ to a maximum value of -9.9‰. There appeared to be an oscillating signal in the isotopic content of the firn core. Periodic maxima of about -10 to -12‰ occurred at depths of 80, 510, 860, 1300, and 1520 cm. The range and oscillations in the 18O values are encouraging and suggest that additional effort is warranted to investigate the possible use of water isotopes to date equatorial ice cores. The similar values in slope between our local meteoric water line (8.1) and the global meteoric water line (8.0) suggest an absence of complex kinetic fractionation processes affecting precipitation on the summit of Antisana. However, the enriched deuterium excess value of 12 at Antisana compared to the global mean of 10 suggests that some of the water vapor that formed precipitation was derived from evaporation of localized water sources, such as the Amazon basin.