LGM to Lateglacial vegetation history and climate variability documented in the paleoecological record from Lake Fimon (northern Italy): what sensitive archives tell us about the past.

The past is regarded as the key to understand the present and to predict the future. While instrumental records and written sources report about events of the recent history, reconstructions for older periods rely on information from proxy data. This expression indicates preserved biological and physical characteristics of the environment that can replace direct measurements and extend our understanding of the past far beyond instrumental and written records. Proxy data from lake sediments are bio- and geo-archives of the past and their microbotanical, sedimentological, chronological and geochemical information can be used to reconstruct and constrain temporal changes in vegetation communities and dynamics, depositional processes and climate parameters. High-resolution of stratigraphic investigations is essential to decipher the effects of centennial to millennial scale climate variability pervading the last glaciation. This presentation focuses on the results of a multiproxy investigation on the stratigraphic succession of Lake Fimon (23 m asl, northern Italy) covering the period 31 - 12 ka BP. This period encompasses the whole Last Glacial Maximum (LGM), the most recent period in Earth's history with maximum globally-integrated ice volume (Mix et al. 2001). To account for the regional effects of millennial-scale climate variability on terrestrial ecosystems and sedimentary processes, the use of representative stratigraphic records is essential. In this respect, the Lake Fimon record is unique at the scale of the European subcontinent and proved to be a continuous and multifaceted archive of well-preserved environmental information (Pini et al. 2010; Monegato et al. 2011; Pini et al. submitted). Its exploitation adds value to paleoecological and paleoclimatological investigations south of the Alps. Lake Fimon formed sometimes during the late Middle Pleistocene. Its sediments document a fairly continuous lacustrine and palustrine sedimentation recovered in more than 40 m of total sediment core length. Extended palynological analysis on the 31-12 ka BP core succession revealed a high microbotanical diversity, with rapid compositional changes testifying to the sensitivity of plant descriptors to climatic variations. The main ecological gradient derived from a PCA ordination on pollen data is connected to climate continentality: during the LGM mixed cool temperate forests with Pinus sylvestris/mugo were replaced by Larix forest steppe facing Artemisia and Juniperus semideserts. Warm-temperate broad-leaved trees stepped in only at the onset of the Bølling-Alleröd interstadial. The occurrence of sensitive microbotanical descriptors in the Lake Fimon record allowed to investigate their climatic signature through the quantitative estimation of temperature and precipitation parameters (Tjan, Tjul, Pann, Annual T Range) using the Modern Analogue Technique (MAT; Chevalier et al. 2020). The modern climate values of more than 6100 sites stored in the Eurasian Modern Pollen Database (Davis et al. 2020) and in the Chinese Pollen Database (Herzschuh et al. 2019) were used for past climate inferences. Interestingly, most of the closest modern analogue for the Lake Fimon pollen spectra occur in southern Siberia and in the Urals. Previous authors (Chytrý et al. 2008; Kune? et al. 2008) already identified these areas as hosting ecosystems resembling full-glacial plant communities of Central Europe. Corrections accounting for the impact of low glacial CO2 concentrations on plant water-use efficiency (Prentice et al. 2017, Cleator et al. 2020) were applied to pollen-based estimated moisture parameters. Phases of enhanced seasonality (Annual T Range > 36°C) and cold boreal winters (Tjan between -20°/-25°C), identified in the reconstructed pollen-based climate time series , correspond to periods of forest withdrawal (total Arboreal Pollen < 40%) and dust input evidenced by particle-size data and elemental analysis. The chronological model for the Lake Fimon record allows to match these periods with the timing of Heinrich Stadials 1 and 2. Extreme continental climate spells on the continent thus coincide with episodes of iceberg discharge and ice-rafted debris (IRD) release in the North Atlantic. Research on the Lake Fimon record contributes to the understanding of the impact and timing of LGM atmospheric circulation changes over the North Atlantic on the southern European continent, a topic that still remains largely unknown. The availability of more high-resolution records will hopefully provide insights into the LGM moisture gradients over the large and orographically-complex landscape that characterizes the European continent.