Abstract
Mid-latitude mountain glaciers sensitively respond to local summer temperature changes. Chronologies of past glacier fluctuations based on the investigation of glacial landforms therefore allows for a better understanding of warm-season climate variability at local scale. In this study, we focus on the Holocene, the current interglacial of the last 11,700 years, which remains matter of dispute regarding its temperature evolution and underlying driving mechanisms. In particular, the nature and significance of the transition from the early to mid-Holocene and of the Holocene Thermal Maximum (HTM) are still debated. Here, we apply a new approach by combining in situ cosmogenic 10Be moraine and 10Be-14C bedrock dating from the same site, the forefield of Steingletscher (European Alps), and reconstruct the glacier’s millennial recession and advance periods. The results suggest that subsequent to the final deglaciation at ~10 ka, the glacier was mostly smaller than its 2000 CE extent until ~3 ka, followed by the predominant occurrence of glacier advances until the end of the Little Ice Age in the 19th century. These findings agree with existing proxy records of Holocene summer temperature and glacier evolution in the Alps, showing that glaciers throughout the region retreated beyond modern extents for most of the Early and mid-Holocene. This implies that at least the summer climate of the HTM was warmer than that of the end of the 20th century for several millennia. Further investigations are necessary to refine the magnitude of warming and the potential HTM seasonality.
Highlights
Mountain glaciers in most glacierized regions of the world, such as the European Alps, are currently rapidly retreating in response to accelerating global warming, driven by human-induced greenhouse gas emissions into the atmosphere (IPCC 2007, 2013, 2021)
Chemical processing was carried out at the Lamont-Doherty Earth Observatory (LDEO) Cosmogenic Nuclide Laboratory (New York, USA) according to the standard procedures described in Schaefer et al (2009) and at the Laboratoire National des Nucléides Cosmogéniques (LN2C) at the Centre Européen de recherche et d’Enseignement des Géosciences de l’Environnement (CEREGE, Aix en Provence, France) following routine methods described for example in Protin et al (2019). 10Be/9Be ratios were measured at the Lawrence Livermore National Laboratory – Center for Accelerator Mass Spectrometry (LLNL-CAMS) and at Accélérateur pour les Sciences de la Terre, Environnement, Risques (ASTER) at CEREGE
In the text and in the figures, the individual ages are presented with their analytical uncertainties only, while moraine mean ages are presented in the text and in the figures with their full uncertainties, i.e., standard deviation and production rate error combined through simple error propagation
Summary
Mountain glaciers in most glacierized regions of the world, such as the European Alps, are currently rapidly retreating in response to accelerating global warming, driven by human-induced greenhouse gas emissions into the atmosphere (IPCC 2007, 2013, 2021). The current interglacial Holocene followed the end of the last glacial period ∼ 11 700 years ago and is characterized by moderate climate variations, including both colder-thantoday and warmer phases (Mayewski et al, 2004; Wanner et al, 2008). The response of mountain glaciers to these Holocene warm periods remains unclear, because records of when and how long mountain glaciers have receded to modern extents or beyond are still scarce and challenging, because much of the potential evidence is buried beneath ice
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