Past climate archives show the Last Interglacial (LIG) period as similar to slightly warmer than current temperatures. However, there is a lack of LIG proxy evidence regarding variations of the climate across large topographic features and how this manifests at different altitudes. Here, we analysed two flowstones from Bigonda Cave, northeast Italy, to reconstruct LIG climate conditions in a region where precipitation is strongly influenced by the presence of the Alps. Stable isotope ratios, trace element concentrations and speleothem petrography from 133 ka to 105 ka allowed the detection of various hydroclimate and environmental conditions. Composite speleothem δ18O records from northeast Italy were found to closely follow the Northern Hemisphere summer insolation curve, attesting to the influence of solar isolation on Earth's hydroclimate. Our reconstructions indicate a northward shift of the Intertropical Convergence Zone during the LIG maximum, permitting Atlantic-derived moisture to travel further east across North Africa than at present, before being directed north towards the Alps. The latter part of the LIG exhibited frequent, extreme precipitation events in the SE Prealps due to orographic lifting of moisture from both the Atlantic and Mediterranean seas. Socio-economic planning must prepare for extreme autumnal flooding events and serious summer droughts, particularly important in vulnerable mountainous regions.
Bibliographical noteFunding Information:
This project has received funding from the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement no. PCOFUND-GA-2008-226070 - project “Trentino”. We thank the Autonomous Province of Trento and Gruppo Grotta Selva di Grigno for permitting sampling in BG Cave. Fieldwork was carried out with R. Miorandi (Museo delle Scienze, Trento). Laboratory work was aided by M. Wimmer and G.E. Moseley (University of Innsbruck), S. Eggins (Australian National University, Canberra) and A. Min (University of Minnesota). We are indebted to the researchers that provided data used in this study. Fig. 1 was produced with help from M. Möllhoff (DIAS, Dublin, Ireland) and M. Zandonati (Museo delle Scienze, Trento). We thank editor M. Bar-Matthews and two anonymous reviews for their insightful suggestions.
The end of the deglacial period is identified in the BG Cave flowstones at 129 ? 1 ka by a sharp increase in the ?18O values, indicating a significant decrease in the contribution of plateau-derived glacial meltwater to infiltration ( Figs. 7 and 8b). A shift to more negative ?13C values and an increase in Mg concentrations support the hypothesis of an increasing contribution from valley flank-derived infiltration, whose catchment is entirely in dolomite. The decreasing trend to more negative flowstone ?13C values point to soil formation in the infiltration zone (cf. Scholz et al., 2012). Moreover, the low and stable concentrations of P indicate that much of the available P was being sequestered by a fast growing vegetation. This suggests that warmer, interglacial conditions had already commenced, given that soils at this elevation need several hundreds of years to develop after a deglaciation (Egli et al., 2006). Therefore, the ?13C values and Mg and P concentrations likely lag the temperature signal. The age of the end of the TII deglaciation phase, as determined from BG Cave flowstones, supports the timing of this event observed in other global archives, including speleothems (Drysdale et al., 2009; Moseley et al., 2015; Wilcox et al., 2020; Bar-Matthews et al., 2003; Cheng et al., 2009; Kelly et al., 2006) and ice cores (Masson-Delmotte et al., 2010) (see Fig. 9).The trace element records of BG2 reveal a few ?anomalous? (wet/cold) events with durations of approximately 200?300 years, within the early LIG (arrows in Fig. 7). At ?127.0 ka, a large Sr spike (>100 ?g g?1) and a dissolution horizon occur. The ?125.0 ka and ?124.1 ka events are identified clearly with positive peaks in the Al and Fe concentrations, which can be associated with inflow of micro-debris and clays. The 124 ka event is particularly prominent with the highest concentrations of Mg, Sr and Al, and lowest concentrations of P, for the entire BG2 record, and is also recorded by a positive ?13C peak. This event is marked by the characteristic orange lamina that separates the deposition style of BG2 from typical flowstone to pool deposits ( Figs. 3 and 5). Here, the short-lived negative spike in P concentrations in BG2 is possibly an artefact caused by a speleothem fabric that is incompatible with the incorporation of P ions. The high concentrations of the metal trace elements suggest cave flooding that injected into the system or reworked particulate micro-debris derived from cave sediments and Sr-rich loess-derived deposits. These short events are here interpreted as very wet periods, causing cave flooding in response to short-lived cooling, which resulted in higher humidity on the northern facing slopes of the Valsugana Valley. Evidence for regional cooling at ?128.0 ka has been found in pollen records from Lago Grande di Monticchio (Brauer et al., 2007) and in speleothems from SW France (Wainer et al., 2011). Data from speleothems from the Schrattenkarst, Switzerland, show cooling events centred at 125.5 ? 0.5 ka and at 124.7 ? 0.9 ka (Wilcox et al., 2020). The latter is thought to be associated with the C27 cold event, caused by an outburst flood from the Hudson Strait and possible major ice melt originating from the east Greenland (Tzedakis et al., 2018). The Schrattenkarst speleothems provided the first well-constrained timing for the C27 cold event in central Europe (Wilcox et al., 2020). Our data showing a 124.1 ? 1.8 ka event provide evidence concurrent (within the uncertainties) with the 124.7 ? 0.9 ka event of Wilcox et al. (2020), and thus, support the hypothesis that the impact of the C27 cold event was more spatially extensive than previously thought and may have been analogous to the 8.2 ka BP event (Nicholl et al., 2012). In the BG2 record, the 124 ka event marks the end of the dry LIG thermal maximum and the onset of wetter conditions. Following the 124 ka event, the Sr concentrations in both BG flowstones reach base level (?20 ?g g?1), marking the almost complete weathering of the Sr-rich loess on the plateau (Fig. 8c).This project has received funding from the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement no. PCOFUND-GA-2008-226070 - project ?Trentino?. We thank the Autonomous Province of Trento and Gruppo Grotta Selva di Grigno for permitting sampling in BG Cave. Fieldwork was carried out with R. Miorandi (Museo delle Scienze, Trento). Laboratory work was aided by M. Wimmer and G.E. Moseley (University of Innsbruck), S. Eggins (Australian National University, Canberra) and A. Min (University of Minnesota). We are indebted to the researchers that provided data used in this study. Fig. 1 was produced with help from M. M?llhoff (DIAS, Dublin, Ireland) and M. Zandonati (Museo delle Scienze, Trento). We thank editor M. Bar-Matthews and two anonymous reviews for their insightful suggestions.
© 2021 Elsevier Ltd
- European alps
- Last interglacial
- Solar insolation
- Stable isotopes
- Trace elements
- U-series dating