Was the Alpine Younger Dryas really dry? New insights from the Italian Dolomites (southern eastern Alps).

After the Last Glacial Maximum, the Alpine Lateglacial was characterized by an alternance of mild interstadials and cold stadials, the former being usually more humid compared to the latter. The youngest of such stadial is called Younger Dryas (YD or Greenland Stadial (GS) 1) and corresponds to the last major glacial advance, with temperatures similar to glacial periods. In the European Alps such phase dates back to ~12.8 to 11.7 ka . Temperature reconstructions suggest a temperature drop during the YD, compared to present, ranging from ~10 °C to 3-4 °C (Koltai et al., 2021). The paleoprecipitation trend in Europe during the YD is debated, with most studies affirming that that the first half of the YD was colder and drier than the second one. Equilibrium line altitude (ELA) reconstructions suggest that the southern Alps were affected by precipitation similar to present values, whilst precipitation in the central part of the Alps was depleted by ~20-30%. However, as can be seen in Fig. 1, such reconstructions are grouped in the central and western sectors of the Alps, with a wide gap comprising the whole eastern side, where our study area is located. We studied the deposits related to the YD in Venegia Valley, a narrow valley located in the Dolomites, about SE-to-NW oriented. The main glacier, which still survives as a very small debris-covered glacier, is named Travignolo, after the pass where it originates. The Travignolo pass (2925 m a.s.l.), separates the two main peaks of the area: the Cimon della Pala (3184 m a.s.l.), to the south, and the Cima della Vezzana (3192 m a.s.l.), to the north. During the YD, the Travignolo glacier was merging with the northern Bureloni and Venegiotta glaciers to form a single tongue that almost reached the exit of the valley, about 6 km downstream, at 1700 m a.s.l.. At its front, this glacier built a well-expressed morainic arc, made of at least three main ridges. Paleoglaciers from the southern Alps show evidence of a double response, whereby the outermost and innermost moraines stabilised at ~12.3±0.7 ka and before 11.2±0.8 ka, respectively (Baroni et al., 2021). Cosmogenic dates performed on boulders located on top of the Venegia Valley frontal moraines confirmed these arcs to be YD in age, well-fitting the older phase. By means of the ArcGIS toolbox "GlaRe" we reconstructed the YD glacier with the AABR method, which gave us a ELA of about 2150 m a.s.l.. With the same approach and basing on the data by Zanoner et al. (2017), we obtained the Little Ice Age (LIA) ELA for the same glacier: 2600 m a.s.l., that is in good agreement with the nearby ELA calculated at Mt. Antelao for the LIA. At the Alpine scale, the obtained LIA depression between the LIA and the YD (i.e., ~450 m) is high, but comparable to the values obtained for the Western and Maritime Alps. Most of all, is the only available data of this kind for the Southern Alps, exception made for a single site in the Maritime Italian Alps. 82 Figure 4: map of the ELA depressions (Little Ice Age value minus Younger Dryas value) in the European Alps, with the location of the study area (yellow star) (modified from Baroni et al., 2021). The obtained data allow for an inference of paleoprecipitations and/or paleotemperatures occurring at the time of glaciers' growth by means of the diagrams developed by Ohmura and Boettcher (2018) and Rea et al. (2020). The summer temperature depressions calculated for the YD (Heiri et al., 2007) and the LIA (e.g., Frank et al., 2010) suggest a marked increase in precipitations (up to double of present values). On the contrary, postulating percentage variations in respect to current precipitations would result in an unrealistic temperature drop (>3°C in respect of the independent reconstructions). In the Dolomites, a recent study suggested the occurrence of a snow-rich early YD that evolved into a snow-poor late YD autumns and early winters (Koltai et al., 2021). This is in good agreement with our results, that suggest an increase in precipitation. Such an increase may be the result of the larger amount of snow precipitation, even if the annual precipitation amount may be not that large as the diagrams suggest.