Preprint of Kern Z., Molnár, M., Palcsu, L. Pavuza R. (2018) Age estimates on the deposition of the cave ice block in the Saarhalle Dachstein-Mammoth Cave (Mammuthöhle, Austria) based on 3 H and 14 C. RADIOCARBON 60: 1379-1389. DOI:10.1017/RDC.2018.96 AGE ESTIMATES ON THE DEPOSITION OF THE CAVE ICE BLOCK IN THE SAARHALLE DACHSTEIN-MAMMOTH CAVE (MAMMUTHÖHLE, AUSTRIA) BASED ON 3 H AND 14 C Kern Z 1,2 *, Palcsu L 2 , Pavuza R 3 , Molnár M 2 1. Institute for Geological and Geochemical Research, Research Centre for Astronomy and Earth Sciences, MTA, Budaörsi út 45., Budapest, H-1112, Hungary 2. Isotope Climatology and Environmental Research Centre (ICER), MTA ATOMKI, Bem tér 18/c, Debrecen, Hungary 3. Working Group of Karst and Cave Science at the Natural History Museum Vienna, Burgring 7, Vienna, Austria Correspondence to: Zoltán Kern; E-mail: kern.zoltan@csfk.mta.hu Abstract Measurements of the radiocarbon and tritium activity in a 5.8 m long ice core from the Saarhalle, Dachstein-Mammoth Cave allowed a substantial revision of previous opinions concerning the age of the ice block, and provide useful experience that may be applied to future 14 C dating of cave ice deposits. The stepped combustion technique results in a remarkably older radiocarbon age for the 800°C than for the 400°C fractions of the carbonaceous matter from ice layer samples. The highest tritium activity (37.2±1.2 TU) can be linked to the period of anthropogenically increased tritium activity of atmospheric precipitation at the mid-1960s, providing a well-dated radiochemical reference horizon. Compared the 3 H-based extrapolated ages of two shallow samples to the expected atmospheric signal an average 14 C reservoir bias of ~1500 BP was obtained for the insoluble organic fraction combusted at 400°C. The conventional 14 C age measured for the 400°C fraction of the deeper samples has been corrected with the average reservoir bias. The median calibrated age of the deepest analyzed sample of the ice profile is ~1830 cal BC and a linear extrapolation to the bottom ice layer gave 2590 cal BC making Saarhalle ice block among the oldest dated cave ice deposits known in the Alpine domain. Keywords: cave ice, tritium, ice core, stepped combustion, insoluble organic material, Holocene, Alps INTRODUCTION One of the most important issues when considering sub-surface ice deposits and their potential use as paleoclimate archives is their age (Luetscher et al. 2013). There might be plenty of options for dating near-surface cave ice deposits (Luetscher et al. 2007; Kern 2018). Radiocarbon ( 14 C) analysis has became the most frequently-used option, allowing the direct dating of cave ice sequences, at least when sufficient organic remnants are to be found (e.g., Hercmann et al. 2010; Perşoiu and Pazdur 2011; Sancho et al. 2012, 2018; Spötl et al. 2014; Gradziński et al. 2016; Munroe et al. 2018; Perşoiu et al. 2017). However, the dating of cave ice bodies settled deep in the high mountain karstic environment is often a great challenge due to the relative scarcity of embedded organic materials (e.g. May et al. 2011). A novel dating approach was introduced a decade ago, targeting glacier ice cores, and based on extracting at the microgram level organic carbon fractions embedded in the ice matrix for 14 C dating (Jenk et al. 2006, 2007). The approach was first tested on samples derived from