Sub-seasonally resolved δ18O, δ13C, Mg, Sr, Ba, U and Zn records from a Belgian speleothem covering the last 700 years

Every cave system is unique and every stalagmite has its own behavior. A good understanding of what the measured proxies are reflecting is therefore needed when reconstructing the paleoclimate at high-resolution by the use of stalagmites. Generally such information is obtained by cave monitoring and/or by comparing the measured records with other paleoclimate records in the region. The stalagmite presented in this study displays an extremely high growth rate (1mm/y) and annual lamination over the last 700 years allowing to compare the measured proxy values with the instrumental record leading to a robust understanding of its climate transfer function. The age model is established by layer counting and is in good agreement with 4 U/Th-ages and one 14C-age confirming the seasonal character of the layering. A one-year cave monitoring with a two-week cave visiting frequency is done to follow how the different proxy signals are recorded in the modern calcite and how they are linked to the outside cave conditions. Sub-seasonal ?18O and ?13C measurements (3 samples a layer) were carried out on the upper 50 years. The remaining 650 years were sampled for isotopes on a seasonal scale by drilling one sample a layer. LA-ICP-MS measurements for Mg, Sr, Ba, U and Zn concentrations were line tracked on the upper 50 years and will be compared with the sub-seasonally resolved isotope records. Cave monitoring results show that the ?18O and ?13C values of fresh glass-slab calcite increase from November to April when the cave temperatures decrease and the drip rate increase. Results from the sub-seasonal isotope sampling show that the ?18O and ?13C values increase within the white more porous layers and decrease in the dark more compact layers. Consequently, white layers are formed during wetter and colder periods while dark layers reflect drier and warmer conditions. Further comparison of the sub-seasonal isotope and trace elemental records with instrumental data will provide a good understanding of the transfer functions of these records for the last 50 years. In a next step, these transfer functions will be used to interpret the full 700-year seasonal isotope record providing a reliable paleoclimate reconstruction for southern Belgium.