Isotopic and time series investigations of recent stalagmites (1945–2018), Schlossberg tunnels, Graz, Austria: implications for climate change in Central Europe

Abstract

AbstractFor the first time, we present a decadal-scale stable isotope record (δ18O, δ13C) of 67 speleothem calcite samples coming from an artificial tunnel network located in Graz, Austria. Stable isotope data are interpreted with the help of time series (TS) analysis of mean air temperatures (MAT) and mean annual precipitations (MAP) that have been monitored and recorded in a neighbouring meteorological station. Speleothem records have proved to be very useful in reconstructing changes of environmental conditions. For studied stalagmites, which grew between 1945 and 2018, the δ18O values average −18.64‰ and range from −23‰ to −17‰ (VPDB, Vienna Pee Dee Belemnite), suggesting variable climatic conditions. The δ18O values of calcite increase along the growth axis and are correlated with high temporal resolution MAT, MAP and weighted mean annual δ18O of precipitations. For the same time interval, while the temperature TS show an increasing trend, with a steeper gradient since the 1980s, the precipitation TS presents a weak decreasing tendency. Increase in the δ13C values of speleothems from −33‰ to −24‰ (VPDB) is correlated with increasing temperature and drought, associated CO2 degassing and soil erosion over the tunnel system.