A common isotope climatology from two new Bolivian ice-cores over the last three centuries

Two new icecores were drilled in the subtropical part of the Andes. The first one, 137 meters long, was extracted from the ice sheet of the Illimani (16{ ~}37'S, 67{ ~}46'W), a 6350m high mountain in the southern part of the Cordillera Real, Bolivia. The second one, 40 meters long, stems from the Sajama (6542 m, 18{ ~}06'S, 68{ ~}53'W), situated in the western part of the Bolivean Highlands. The isotopic composition of the ice as well as a number of various tracers (dust, calcium ions, electric conductivity) were analysed in the laboratory and used for a year-by-year dating of the ice. A detailed comparison between the isotope signal of four different Andean high altitude sites (Huascarán, Quelccaya, Illimani and Sajama) show a nearly identical inter-annual variability in the 20th century. This is a remarkable result since the regional climate response to tropical interannual climate variability, principally ENSO, is quite different between these sites distributed over a huge area from 9{ ~}S to 18{ ~}S. Furthermore, we analyse the results of a 92-year integration of the ECHAM general circulation model which was fitted with water isotope diagnostics and we conclude that the Andean high altitude records archive the variability of the water isotopes over the entire expanse of tropical/subtropical South America. The isotopes are strongly affected by water vapour recycling, and therefore principally temperature variability, in the Amazone basin. Three of the records discussed here (Huascarán, Quelccaya, Illimani) extent back to the 17th century and allow therefore a comparison between the strong decadal variability of the isotope signal seen in the last century relative to the former two centuries.