Tree-rings analysis for reconstructing alpine glaciers mass balance and climatic changes in the Rhaetian Alps during the last millennium

The rise of the global mean temperature with an unprecedented recorded rate is well documented. Nevertheless, the knowledge of the past climate variations is fundamental for better understanding the ongoing climate change. This need is especially important in high mountain areas, where the effects of global warming are amplified and induce an accelerated glacial retreat. Thus, the use of proxies sensible to climatic parameters such tree-ring width and maximum wood density offer tools to better comprehend the environmental dynamics in these sensible sites. To investigate the potential of deriving high quality temperature and glacier mass balance information from tree-rings, such as tree-ring width (TRW) and maximum density (MXD) chronologies were built from two alpine species Larix decidua Mill. and Pinus cembra L., sampled at around 2000 m a.s.l. on the Adamello-Presanella and Ortles-Cevedale massifs in the southern Rhaetian Alps. Here are presented two larch-based short summer (June to August) mean temperatures reconstructions. The Bosco Antico chronology, a six-centuries long dataset from the most ancient living wood in Val di Sole area (Southern Rhaetian Alps, Italy) and the European Larch composite chronology, built using hundred series from both the massifs. The former spans from 1475 to 2015 and preserves a higher mid-term variability the latter spans from 1502 to 2016, preserves a more restricted variability but is less influenced by local effects. Both the chronologies well represented the long-term variability of the site. Moreover, a pine-based long summer (May to September) mean temperatures reconstruction is presented. The inferred temperatures perfectly overlap with the glaciers ablation season of the area. The proposed chronology spans from 1825 to 2015, and its potential as a temperature as well as glacier mass balance proxy is assessed. The obtained results, permit to reconstruct the summer mass balance of the Careser Glacier at annual resolution back to 1825 and the annual mass balance back to year 1901. The inferred quantity of net water equivalent loss during the last century was estimated to be around 89 m w.e. with a mean rate of 0.8 m w.e. year^-1. The water equivalent loss during only the ablation season since 1823 was estimated to be around 307 m w.e. All the obtained results perfectly match with the geomorphological evidences obtained during previous field surveys. The results add an important dataset for a particular climatic area, allow to better understand the climate dynamics improving local as well as regional climate reconstructions. Moreover, the reconstruction of a glacier mass balance was assessed for the first time in the southern Rhaetian Alps representing a milestone for better understanding the glacier responses to the past climatic variations as well as to the ongoing climate change.