Tropical Glacier and Ice Core Evidence of Climate Change on Annual to Millennial Time Scales

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Abstract

This paper examines the potential of the stable isotopic ratios, 18O/16O (δ18Oice) and 2H/1H (δDice), preserved in mid to low latitude glaciers as a tool for paleoclimate reconstruction. Ice cores are particularly valuable as they contain additional data, such as dust concentrations, aerosol chemistry, and accumulation rates, that can be combined with the isotopic information to assist with inferences about the regional climate conditions prevailing at the time of deposition. We use a collection of multi-proxy ice core histories to explore the δ18O-climate relationship over the last 25,000 years that includes both Late Glacial Stage (LGS) and Holocene climate conditions. These results suggest that on centennial to millennial time scales atmospheric temperature is the principal control on the δ18Oice of the snowfall that sustains these high mountain ice fields.

Decadally averaged δ18Oice records from three Andean and three Tibetan ice cores are composited to produce a low latitude δ18Oice history for the last millennium. Comparison of this ice core composite with the Northern Hemisphere proxy record (1000–2000 A.D.) reconstructed by Mann et al. (1999) and measured temperatures (1856–2000) reported by Jones et al. (1999) suggests the ice cores have captured the decadal scale variability in the global temperature trends. These ice cores show a 20th century isotopic enrichment that suggests a large scale warming is underway at low latitudes. The rate of this isotopically inferred warming is amplified at higher elevations over the Tibetan Plateau while amplification in the Andes is latitude dependent with enrichment (warming) increasing equatorward. In concert with this apparent warming, in situ observations reveal that tropical glaciers are currently disappearing. A brief overview of the loss of these tropical data archives over the last 30 years is presented along with evaluation of recent changes in mean δ18Oice composition. The isotopic composition of precipitation should be viewed not only as a powerful proxy indicator of climate change, but also as an additional parameter to aid our understanding of the linkages between changes in the hydrologic cycle and global climate.