Cryogenic cave carbonates in the Dolomites (Northern Italy): insights into Younger Dryas cooling and seasonal precipitation

Abstract. In the European Alps, the Younger Dryas (YD) was characterized by the last major glacier advance with equilibrium line altitudes being ~ 220 to 290 m lower than during the Little Ice Age and also by the development of rock glaciers. Dating of these geomorphic features, however, is associated with substantial uncertainties leading to considerable ambiguities on the internal structure of this stadial, the most intensively studied one of the last glacial period. Here we provide robust physical evidence based on precise 230Th-dated cryogenic cave carbonates (CCC) coupled with thermal modelling indicating that early YD winters were only moderately cold in the Southern Alps, challenging the commonly held view of extreme YD seasonality. Our data argue for a negative temperature anomaly of ≤ 3 °C in mean annual air temperature at the Allerod-YD transition in a mountain cave (Cioccherloch, 2274 m a.s.l.) in the Dolomites of northern Italy. Our data suggest that autumns and early winters in the early part of the YD were relatively snow-rich, resulting in a stable winter snow cover. The latter insulated the shallow subsurface in winter and allowed the cave interior to remain close to the freezing point (0 °C) year-round, promoting CCC formation. The main phase of CCCs precipitation at ~ 12.2 ka BP coincides with the mid-YD transition recorded in other archives across Europe. Based on thermal modelling we propose that CCC formation at ~ 12.2 ka BP was most likely associated with a slight warming of approximately +1 °C in conjunction with drier autumns and early winters in the second half of the YD. These changes triggered CCC formation in this alpine cave as well as ice glacier retreat and rock glacier expansion in the Alps.