High-resolution ecosystem changes pacing the millennial climate variability at the Middle to Upper Palaeolithic transition in NE-Italy

Observation of high-resolution terrestrial palaeoecological series can decipher relationships between past climatic transitions, their effects on ecosystems and wildfire cyclicity. Here we present a new radiocarbon dated record from Lake Fimon (NE-Italy) covering the 60–27 ka interval. Palynological, charcoal fragments and sediment lithology analysis were carried out at centennial to sub-centennial resolutions. Identification of the best modern analogues for MIS 3 ecosystems further enabled to thoroughly reconstruct structural changes in the vegetation through time. This series also represents an “off-site” reference record for chronologically well-constrained Palaeolithic sites documenting Neanderthal and Homo sapiens occupations within the same region. Neanderthals lived in a mosaic of grasslands and woodlands, composed of a mixture of boreal and broad-leaved temperate trees analogous to those of the modern Central-Eastern Europe, the Southern Urals and central-southern Siberia. Dry and other grassland types expanded steadily from 44 to 43 ka and peaked between 42 and 39 ka, i.e., about the same time when Sapiens reached this region. This vegetation, which finds very few reliable modern analogues in the adopted Eurasian calibration set, led to the expansion of ecosystems able to sustain large herds of herbivores. During 39–27 ka, the landscape was covered by steppe, desert-steppe and open dry boreal forests similar to those of the modern Altai-Sayan region. Both Neanderthal and Sapiens lived in contexts of expanded fire-prone ecosystems modulated by the high-frequency climatic cycles of MIS 3.

The sedimentological structures observed in Fimon PD (21.75 -19.39 m) and TdA (31 -26 m) core sections and the high-resolution record of limnic algae and aquatic plants from Fimon PD core (Fig. S2) suggest that deposition took place in a shallow lacustrine environment for most of the MIS 3 interval (FL3 lithostratigraphic zone, Fig. S1-2). In this context, massive grey clay intervals containing very high siliceous + oxides values (90% of the dry weights) alternate with several organic-rich (silty gyttja) layers marked by flooded littoral zones expansion suggesting a deepening of the water column (FL3b, e, h, g and i;  S2). The peat interval is attributed to long-lasting marshy conditions occupying a wide area as recorded by the finding of the same peat layer in the three studied cores 8,9 . During this phase accumulation rates increased from ca. 0.006 to 0.02 cm/years due to favourable (local) biomass growth under relatively humid conditions 10 . A sequence of laminated minerogenic silts rich in limnic algae (FL6; Fig. S2) overlayed these terrestrial organic deposits indicate a freshwater input that drowned the mire (see 10 for further information). and a landslide unit (D) 11 . Macro-unit A, which is the focus of our study, includes several horizontal layers from A13 to A1, ranging from layers dominated by residual dolomite sands (layers A13-A12), angular fine to medium-sized stone layers (levels in the A10 complex, layers A7, A4), stones, slabs and fine material (layer A3) or anthropogenic material (A11, levels in A10 and A9 complexes, A6, A2-A1) 12 . Unit A shows evidence of much more intense human occupations, which include (Final) Mousterian (A11, A10 A9, A6-A5, A4), Uluzzian (A3) and Proto-Aurignacian (A2-A1) assemblages [13][14][15] . Landslide Unit D mostly consists of large blocks, which collapsed from the cavity's roof because of macrogelivation processes. Evidence of human occupation is present within the lowermost layers D3d, D3b and D3a, representing the latest Aurignacian units 16 (11, 9, 7 and 4) contain Mousterian artefacts, faunal remains and clearly differentiate in dark-brownish color from the other units.

San Bernardino
Grotta Maggiore di San Bernardino (Mossano, Berici Hills, Vicenza), located at 135 m a.s.l., lies in the foreland of the eastern Italian Alps. The cave opens along the eastern slope of the karst plateau of the Berici Hills on a carbonate sandstone cliff from the Middle Eocene, facing the alluvial plain of the Bacchiglione River and the south-western sector of the Euganean Hills. The cave is 41 m long, 7 m wide and 9 m high and was produced by thermoclastic processes and chemical dissolution, which widened deep, SE-NW oriented fractures. In the western side of the same slope, a second, shorter cave named Grotta Minore di San Bernardino is situated. The first archaeological excavations were carried out by Prof. P. Leonardi in the 1960s in the area facing the medieval wall, uncovering a Pleistocene sequence with faunal remains and knapped stones 23,24 . A second cycle of research, between 1986 and 1995, allowed a more detailed reexamination of the different facies of the stratigraphic series between the inner and outer zones of the cave 25  Cave as a place where carcasses processing was finalized, after an initial process at the kill-site, and then prepared for consumption 26 .

SI-3
Archaeozoological data The presence of freshwaters is also evidenced by findings of beaver and moose remains.
Afterwards, between ca. 44-39 ka, major ecological changes occurred in faunal assemblages. In stratigraphic reference sequences we notice a consistent decrease of  cores, plotted versus their original depth. 14 C ages are plotted according to their stratigraphic position. Radiocarbon ages indicated in red were excluded from our modelling since they mostly yielded age reversals, as previously demonstrated 8,41 . Magnetic susceptibility, LOI-determined total organic matter including sulphides, CaCO3 including sulphides and sulphates and residuum, accompanied by the percentage curves of Pinus sylvestris/mugo type, Artemisia and Cichorioideaea were used to correlate the sequences.
Also, data shows the reproducibility of the two Lake Fimon records.          Table S1 -Coordinates and metadata for the best (first) modern analogues of Fimon PD fossil pollen spectra. Low similarity/non analogue situations are highlighted in bold type.

Figure S9
-Comparison between Fimon PD pollen data: sum of grasslands (Cichorioideae, Anthemis type, Aster type, Xeranthemum inapertum type, Ranunculaceae, Geranium molle type Ephedra fragilis type, Ephedra distachya type); steppe (Artemisia, Chenopodiaceae, Hippophae) and squared-chord distance curves for the calibration set, distances smaller than the 5th percentile of all distances between the calibration set samples are "good analogues", while distances larger than the 10 th percentile are "non-analogue" assemblages 46 .