A novel radiocarbon dating technique applied to an ice core from the Alps indicating late Pleistocene ages

International audienceIce cores retrieved from high-altitude glaciers are important archives of past climatic and atmospheric conditions in midlatitude and tropical regions. Because of the specific flow behavior of ice, their age-depth relationship is nonlinear, preventing the application of common dating methods such as annual layer counting in the deepest and oldest part. Here we present a new approach and technique, allowing dating of any such ice core at arbitrary depth for the age range between ∼500 years B.P. and the late Pleistocene. This new, complementary dating tool has great potential for numerous ice core related paleoclimate studies since it allows improvement and extension of existing and future chronologies. Using small to ultrasmall sample size (100 μg > carbon content > 5 μg) accelerator mass spectrometry, we take advantage of the ice-included, water-insoluble organic carbon fraction of carbonaceous aerosols for radiocarbon (14C) dating. Analysis and dating of the bottom ice of the Colle Gnifetti glacier (Swiss-Italian Alps, 45°55′50″N, 7°52′33″E, 4455 m asl) has been successful in a first application, and the results revealed the core to cover most of the Holocene at the least with indication for late Pleistocene ice present at the very bottom