The ice on Mont Blanc has archived aerosols in Europe since the last deglaciation
A study published in PNAS Nexus documents for the first time the evolution in Europe of different aerosols (sea salt, dust, biotic particles) over the last 12,000 years. These measurements of d18O and various chemical compounds come from an ice core taken at 4,300 m near the summit of Mont Blanc and dated, among other things, by 14C. This unique archive documents the link between aerosol and climate outside the polar regions, in this case Western Europe.
Atmospheric aerosol, a fine liquid or solid particle in the atmosphere, is a key player in regional climate that remains poorly understood. Ice simultaneously archives past climate and aerosol. However, until now, the study of glacial records has not made it possible to examine the aerosol-climate link since the last ice age, except in the polar regions. This lack of data at mid-latitudes is crucial for Europe which, in addition to climatic fluctuations, has experienced anthropogenic pressure long before the start of the industrial era, with the modification of land use during the last millennia of the Holocene by the first agricultural societies.
Carbon-14 measurement and past temperature profile
Scientists from 3 countries and 2 French laboratories (see box) have identified a drilling site on a glacier in the French Alps that has archived the evolution of aerosol in Europe over the last ~12,000 years. Unlike glacier sites, which are often located in a mountain pass, this new borehole is located on a flat summit, which minimises the high stresses caused by the glacier flowing over the ice near the bedrock, a phenomenon that disrupts the climate record beyond a few thousand years. This new ice core was dated using argon air bubbles and the identification of lead pollution during the Roman Antiquity for the most recent part, by measuring 14C on the organic matter and the 18O profile for the early Holocene.
Dating the core extracted near Mont Blanc. Top: lower part of the 18O profile showing the presence of ice from the last ice age. Bottom: Age-depth relationship for the core, based mainly on measurements of 39Ar and 14C. Reference
Chemical analysis of this ice shows an increase in sea salt and dust concentrations over Western Europe during cold periods, corresponding to stronger westerly winds and greater dust emissions, probably from the Sahara. It also indicates a decrease in concentrations of biogenic particles during cold climatic periods, implying a significant reduction in European vegetation cover.
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CNRS Laboratories
Laboratoire inter-universitaire des systèmes atmosphériques (LISA-IPSL)
Institut des géosciences de l’environnement (IGE-OSUG)
Reference
Michel Legrand, Joseph R McConnell, Susanne Preunkert, David Wachs, Nathan J Chellman, Kira Rehfeld, Gilles Bergametti, Sophia M Wensman, Werner Aeschbach, Markus K Oberthaler, Ronny Friedrich, Alpine ice core record of large changes in dust, sea-salt, and biogenic aerosol over Europe during deglaciation, PNAS Nexus, Volume 4, Issue 6, June 2025, pgaf186.
Contact
Michel Legrand, Laboratoire inter-universitaire des systèmes atmosphériques (LISA-IPSL) •
Source: CNRS Terre & Univers.
