Abstract. Annually laminated speleothems allow the reconstruction of paleoclimate down to a seasonal scale. In this study, an annually laminated stalagmite from the Han-sur-Lesse Cave (Belgium) is used to study the expression of the seasonal cycle in northwestern Europe during the Little Ice Age. More specifically, two historical 12-year-long growth periods (ca. 1593–1605 CE and 1635–1646 CE) and one modern growth period (1960–2010 CE) are analysed on a sub-annual scale for their stable isotope ratios (δ13C and δ18O) and trace element (Mg, Sr, Ba, Zn, Y, Pb, U) content. Seasonal variability in the proxies is confirmed with frequency analysis. Zn, Y and Pb show distinct annual peaks in all three investigated periods related to annual flushing of the soil during winter. A strong seasonal in phase relationship between Mg, Sr and Ba in the modern growth period reflects a substantial influence of prior calcite precipitation (PCP). In particular, PCP occurs during summers when recharge of the epikarst is low. This is also evidenced by earlier observations of increased δ13C values during summer. In the 17th century intervals, there is a distinct antiphase relationship between Mg, Sr and Ba, suggesting that varying degrees of incongruent dissolution of dolomite control the observed seasonal variations. The processes controlling seasonal variations in Mg, Sr and Ba in the speleothem appear to change between the 17th century and 1960–2010 CE. The Zn, Y, Pb and U concentration profiles, stable isotope ratios and morphology of the speleothem laminae all point towards increased seasonal amplitude in cave hydrology and higher drip water discharge during the 17th century. These observations reflect an increase in water excess above the cave and recharge of the epikarst, due to a combination of lower summer temperatures and increased winter precipitation during the 17th century. This study indicates that the transfer function controlling Mg, Sr and Ba seasonal variability varies over time. Which process is dominant, either PCP or dolomite dissolution, is clearly climate-driven and can thus be used as a paleoclimate proxy itself.
Reconstructing seasonality through stable isotope and trace element analysis of the Proserpine stalagmite, Han-sur-Lesse Cave, Belgium: indications for climate-driven changes during the last 400 years