Multiproxy reconstruction of the annual signal in a temperate glacier: the Adamello ADA270 ice core

Temperate glaciers have been considered unreliable palaeoclimate archives due to the possible snow melting and consequent loss of physical and chemical signals of the ice. The Adamello Glacier is located on the southern slopes of the European Alps (Italy), at an altitude included between 2560 and 3420 m a.s.l. In 2021, a 224 m long ice core was drilled in the framework of ClimADA project. In this glacier, the ice has an accumulation rate of ca 0.9 m a−1; a sampling resolution of 10 cm was chosen, thus ensuring palaeoclimate reconstructions at subannual scale. Preliminary analyses show that a seasonal pattern is preserved: a spring-summer layer rich in particles constitutes up to 10 % of the annual ice thickness while 90 % is formed by autumn-winter clean ice. Given the good preservation of insoluble particles, a multiproxy approach based on the simultaneous counting of eight particle types was chosen. Even if the particle-rich layers are rarely visible to the naked eye from a depth of 41 m downward, the seasonal signal is well preserved also in the deeper part of the core. This preliminary investigation demonstrates that insoluble particles reached the Adamello Glacier from at least two diverse sources: the slopes of the Adamello Massif, and a long-distance source that is identified as the Sahara Desert. Temperate glaciers, therefore, can be valuable archives especially for insoluble particles; the high deposition rate of snow allows detailed paleoenvironment reconstructions. Though time consuming, the contemporaneous counting of many proxies greatly enhances the available information.