The isotopic composition of the French Illimani ice core in the Bolivian Andes supports the east-west South American precipitation dipole from the last deglaciation to the mid-Holocene

Abstract

The age of the deepest part of the French Illimani ice core drilled in 1999 in Bolivia (16.63°S, 67.78°W) has been attributed to the Last Glacial Maximum (LGM). Major uncertainties remain on this initial dating, as it is based on the overall similarity in the isotopic composition of the ice between the Illimani and Huascarán (Peru, 9.11°S, 77.61°W) ice cores. Here, we use available measurements of atmospheric isotopic composition (δ¹⁸O_atm) over the last 5 m of the Illimani ice core to propose a revised dating. The age of the bottom of the Illimani ice core is now estimated at between 14.5 ka BP and 15.2 ka BP, covering a period from the end of the Heinrich stadial 1 to the mid-Holocene. Millennial and orbital variations of the isotopic composition of Illimani ice (δD) over this period are now consistent with records of the isotopic composition of speleothems (δ¹⁸O) located on the western pole of the east-west tropical South American precipitation dipole. We also discuss, for the first time for an Andean ice core, the continuously measured deuterium excess profile of the Illimani ice. The latter appears to be a promising new candidate for discussing vegetation changes that may have occurred in the Amazon basin during the last deglaciation.