Geology

Not As Dry As Dust

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Science  01 Aug 2003:
Vol. 301, Issue 5633, pp. 567
DOI: 10.1126/science.301.5633.567b

Two long ice cores were drilled into glaciers in the high Andes during the 1990s, at Huascarán in Peru and farther south at Sajama in Bolivia. These cores provide climate records that extend backward into glacial periods in the tropics. Such long and continuous records are scarce and have been particularly important for assessing the role of the tropics in climate change and for evaluating how early civilizations in the region were affected by and coped with climate change. Both of these cores record the overall warming of the region at the end of the Ice Age, as marked most prominently by a change in the oxygen isotope composition of the ice. One interpretation is that this primarily reflects regional warming, perhaps by as much as 5° to 12°C during deglaciation, but some of the isotopic signal could reflect a shift in moisture sources. There are also several differences between the cores that may be due to local conditions, and understanding these differences is critical for deciphering the deglaciation history of the tropics.

Ramirez et al. have obtained and analyzed a third ice core from Nevado Illimani in the high Andes of Bolivia, north of Sajama. It too extends back to the Ice Age and agrees more closely with the Huascarán core, rather than the proximal Sajama core. Comparisons of these three cores and other records from tropical South America imply that glacial times in this region were particularly cold and wet, that some of the isotopic signal may reflect this additional moisture, and that parts of the Holocene record of Sajama may have been affected by local conditions. — BH

Earth Planet. Sci. Lett. 212, 337 (2003).

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