Significant mass loss in the accumulation area of the Adamello glacier indicated by the chronology of a 46 m ice core

Abstract

Dating glaciers is an arduous yet essential task in ice core studies, which becomes even more challenging when the glacier is experiencing mass loss in the accumulation zone as result of climate warming, leading to an older ice surface of unknown age. In this context, we dated a 46 m deep ice core from the Central Italian Alps retrieved in 2016 from the Adamello glacier in the locality Pian di Neve (3100 m a.s.l.). Here we present a timescale for the core obtained by integrating results from the analyses of the radionuclides 210Pb and 137Cs with annual layer counting derived from pollen and refractory black carbon concentrations. Our results clearly indicate that the surface of the glacier is older than the drilling date of 2016 by about 20 years and that the 46 m ice core reaches back to around 1944. For the period of 1995–2016 the mass balance at the drilling site (former accumulation zone) decreased on average of about 1 m w.e. a−1 compared to the period 1963–1986. Despite the severe mass loss affecting this glacier even in the former accumulation zone, we show that it is possible to obtain a reliable timescale for such a temperate glacier using black carbon and pollen seasonality in combination with radionuclides 210Pb and 137Cs. Our results are therefore very encouraging and open new perspectives on the potential of such glaciers as informative palaeoarchives.