Giant dust particles at Nevado Illimani: a proxy of summertime deep convection over the Bolivian Altiplano

Abstract. A deeper understanding of past atmospheric circulation variability in the Central Andes is a high-priority topic in paleoclimatology, mainly because of the necessity to validate climate models used to predict future precipitation trends and to develop mitigation and/or adaptation strategies for future climate change scenarios in this region. Within this context, we here investigate an 18-years firn core drilled at the Nevado Illimani in order to interpret its mineral dust record in relation to seasonal processes, in particular atmospheric circulation and deep convection. The core was dated by annual layer counting based on seasonal oscillations of dust, calcium and stable isotopes. Geochemical and mineralogical data show that dust is regionally-sourced in winter and summer. During austral summer (wet season) an increase in the relative proportion of giant dust particles (ø > 20 µm) is observed, in association to oscillations of stable isotope records (δD, δ¹⁸O). It seems that at Nevado Illimani both the deposition of dust and the isotopic signature of precipitation are influenced by atmospheric deep convection, which is also related to the total amount of precipitation in the area. This hypothesis is corroborated by local meteorological data. The interpretation of giant particle and stable isotope records suggests that during La Niña years, summer convection activity is enhanced, in agreement with atmospheric circulation studies. Giant particles and stable isotopes, when considered together, can be therefore used as a new proxy for obtaining information about deep convective activity in the past, which is ultimately related to paleo-ENSO variability.